WorldWideScience

Sample records for auroral electrojets

  1. Investigating the auroral electrojets using Swarm

    Science.gov (United States)

    Smith, Ashley; Macmillan, Susan; Beggan, Ciaran; Whaler, Kathy

    2016-04-01

    The auroral electrojets are large horizontal currents that flow within the ionosphere in ovals around the polar regions. They are an important aspect of space weather and their position and intensity vary with solar wind conditions and geomagnetic activity. The electrojet positions are also governed by the Earth's main magnetic field. During more active periods, the auroral electrojets typically move equatorward and become more intense. This causes a range of effects on Earth and in space, including geomagnetically induced currents in power transmission networks, disturbance to radio communications and increased drag on satellites due to expansion of the atmosphere. They are also indicative of where the aurora are visible. Monitoring of the auroral electrojets in the pre-satellite era was limited to the network of ground-based magnetic observatories, from which the traditional AE activity indices are produced. These suffer in particular from the stations' poor distribution in position and so this motivates the use of satellite-based measurements. With polar low-Earth orbit satellites carrying magnetometers, all latitudes can be sampled with excellent resolution. This poster presents an investigation using Swarm's magnetometer data to detect the electrojets as the spacecraft move above them. We compare and contrast two approaches, one which uses vector data and the other which uses scalar data (Hamilton and Macmillan 2013, Vennerstrom and Moretto, 2013). Using ideas from both approaches we determine the oval positions and intensities from Swarm and earlier satellites. The variation in latitude and intensity with solar wind conditions, geomagnetic activity and secular variation of the main field is investigated. We aim to elucidate the relative importance of these factors. Hamilton, B. and Macmillan, S., 2013. Investigation of decadal scale changes in the auroral oval positions using Magsat and CHAMP data. Poster at IAGA 12th Scientific Assembly, 2013. http

  2. Auroral Electrojet Index Designed to Provide a Global Measure, Hourly Intervals, of Auroral Zone Magnetic Activity

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Auroral Electrojet (AE) index is designed to provide a global quantitative measure of auroral zone magnetic activity produced by enhanced ionospheric currents...

  3. Data book for Auroral Electrojet indices

    Energy Technology Data Exchange (ETDEWEB)

    1985-12-01

    The auroral electrojet (AE) indices for the period after 1978 have been published by the World Data Center C2 for Geomagnetism which is operated by the Data Analysis Center for Geomagnetism and Space Magnetism, Faculty of Science, Kyoto University. The Center in publishing the AE indices for every half year on a WDC-C2 for Geomagnetism Data Book. So far the Center has published 7 Data Books for the indices. The AE indices from 1978 to 1981 are published on the Data Book No. 3 to 10 and No. 11 involves the indices for the first half of 1983. The reason why the indices for 1983 has been published prior to that for 1982 is that the analysis group of the ISEE-3 satellite data requested the advanced derivation of the AE indices during magnetotail crossing by the satellite, and the WDC-A for STP (boulder, Colorado) digitized magnetograms necessary for derivation of the indices for the period (October 1982 to December 1983). The Center is now deriving the provisional AE indices during the ISEE-3 tail crossing period. The same data were used for the Data Book No. 11 after usual quality check which was neglected in derivation of the provisional indices. After No. 8 printing and distribution of the Data Book for AE indices are made by National Institute of Polar Research, Tokyo.

  4. Auroral Electrojet Index Designed to Provide a Global Measure, l-minute Intervals, of Auroral Zone Magnetic Activity

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Auroral Electrojet index (AE) is designed to provide a global quantitative measure of auroral zone magnetic activity produced by enhanced ionospheric currents...

  5. Auroral Electrojet Indices Designed to Provide a Global Measure, 2.5-Minute Intervals, of Auroral Zone Magnetic Activity

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Auroral Electrojet index (AE) is designed to provide a global quantitative measure of auroral zone magnetic activity produced by enhanced ionospheric currents...

  6. Real-time determination and monitoring of the auroral electrojet boundaries

    Directory of Open Access Journals (Sweden)

    Johnsen Magnar Gullikstad

    2013-08-01

    Full Text Available A method for nowcasting of the auroral electrojet location from real-time geomagnetic data in the European sector is presented. Along the auroral ovals strong electrojet currents are flowing. The variation in the geomagnetic field caused by these auroral electrojets is observed on a routine basis at high latitudes using ground-based magnetometers. From latitude profiles of the vertical component of these variations it is possible to identify the boundaries of the electrojets. Using realtime data from ground magnetometer chains is the only existing method for continuous monitoring and nowcasting of the location and strength of the auroral electrojets in a given sector. This is an important aspect of any space weather programme. The method for obtaining the electrojet boundaries is described and assessed in a controlled environment using modelling. Furthermore a provisional, real-time electrojet tracker for the European sector based on data from the Tromsø Geophyiscal Observatory magnetometer chain is presented. The relationship between the electrojet and the diffuse auroral oval is discussed, and it is concluded that although there may exist time-dependent differences in boundary locations, there exists a general coincidence. Furthermore, it is pointed out that knowledge about the latitudinal location of the geomagnetic activity, that is the electrojets, is more critical for space weather sensitive, ground-based technology than the location of the aurora.

  7. M and X Class Flares During 2011 to 2013 and their Connection to Auroral Electrojet Indices

    Directory of Open Access Journals (Sweden)

    Debojyoti Halder

    2014-07-01

    Full Text Available Solar bursts recorded in the frequency range 50 to 300 MHz by using log periodic dipole array over Kalyani (22°58´N, 88°46´E have been statistically analyzed for the years 2011-2013. Scatter plots of flare intensity for both M- and X-class flares as well as the number of occurrences of the two categories have been examined. The characteristics of the auroral electrojet indices are correlated directly to the solar flare activity. The auroral indices data obtained from various sources are sorted accordingly. The daily averaged data of the auroral indices are plotted for a period of 5 years, 2009 to 2013. Regression analysis of the indices data has been done meticulously. The regression analysis data are also plotted as residual plots and line fit plots. We have tried to discuss the possible connection between the occurrences of solar flares and the auroral electrojet indices

  8. A classification of spectral populations observed in HF radar backscatter from the E region auroral electrojets

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available Observations of HF radar backscatter from the auroral electrojet E region indicate the presence of five major spectral populations, as opposed to the two predominant spectral populations, types I and II, observed in the VHF regime. The Doppler shift, spectral width, backscatter power, and flow angle dependencies of these five populations are investigated and described. Two of these populations are identified with type I and type II spectral classes, and hence, are thought to be generated by the two-stream and gradient drift instabilities, respectively. The remaining three populations occur over a range of velocities which can greatly exceed the ion acoustic speed, the usual limiting velocity in VHF radar observations of the E region. The generation of these spectral populations is discussed in terms of electron density gradients in the electrojet region and recent non-linear theories of E region irregularity generation.

    Key words. Ionosphere (ionospheric irregularities

  9. Response of the auroral electrojet indices to abrupt southward IMF turnings

    Directory of Open Access Journals (Sweden)

    J. W. Gjerloev

    2010-05-01

    Full Text Available We present results from a study of the behavior of the auroral electrojet indices following abrupt southward turnings of the IMF Bz. The auroral electrojet indices are calculated from observations made by more than 100 ground based stations provided by the SuperMAG collaborators. Based on three simple criteria we selected 73 events. In each event the interval of analysis started at the time of the IMF Bz southward turning and ended 45 minutes later or at the onset of any abrupt energy unloading event in the magnetosphere, regardless of size. We refer to this period as the "pre-unloading phase". To isolate the dependence of the auroral electrojets on the solar induced ionospheric conductivity during this phase we separated the standard AU/AL indices into two new sets of indices defined by the upper and lower envelope of the north-south component for all sunlit stations (AUs/ALs and for all stations in darkness (AUd/ALd. Based on events and statistical analyses we can conclude that following a southward turning of the IMF Bz the AUd/ALd indices show no measurable response while the AUs/ALs indices clearly intensify. The intensifications of AUs/ALs are dependent on the intensity of the solar wind driver (as measured by IMF Bz or the Akasofu ε parameter. The lack of AUd/ALd response does not depend on the intensity of any subsequent substorm.

    We find that during these isolated events the ionospheric current system is primarily confined to the sunlit ionosphere. This truncated version of the classical global DP-2 current system suggests that auroral electrojet continuity is not maintained across the terminator. Because of its conductivity dependence on the solar zenith angle, this truncated global current pattern is expected to be highly dependent on UT and season and thus can be asymmetric between hemispheres. Thus we argue that the global two-cell DP-2 current system

  10. Auroral Electrojet (AE, AL, AO, AU) - A Global Measure of Auroral Zone Magnetic Activity

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The AE index is derived from geomagnetic variations in the horizontal component observed at selected (10-13) observatories along the auroral zone in the northern...

  11. On the relationship between auroral absorption, electrojet currents and plasma convection

    Directory of Open Access Journals (Sweden)

    A. C. Kellerman

    2009-02-01

    Full Text Available In this study, the relationship between auroral absorption, electrojet currents, and ionospheric plasma convection velocity is investigated using a series of new methods where temporal correlations are calculated and analysed for different events and MLT sectors. We employ cosmic noise absorption (CNA observations obtained by the Imaging Riometer for Ionospheric Studies (IRIS system in Kilpisjärvi, Finland, plasma convection measurements by the European Incoherent Scatter (EISCAT radar, and estimates of the electrojet currents derived from the Tromsø magnetometer data. The IRIS absorption and EISCAT plasma convection measurements are used as a proxy for the particle precipitation component of the Hall conductance and ionospheric electric field, respectively. It is shown that the electrojet currents are affected by both enhanced conductance and electric field but with the relative importance of these two factors varying with magnetic local time (MLT. The correlation between the current and electric field (absorption is the highest at 12:00–15:00 MLT (00:00–03:00 MLT. It is demonstrated that the electric-field-dominant region is asymmetric with respect to magnetic-noon-midnight meridian extending from 09:00 to 21:00 MLT. This may be related to the recently reported absence of mirror-symmetry between the effects of positive and negative IMF By on the high-latitude plasma convection pattern. The conductivity-dominant region is somewhat wider than previously thought extending from 21:00 to 09:00 MLT with correlation slowly declining from midnight towards the morning, which is interpreted as being in part due to high-energy electron clouds gradually depleting and drifting from midnight towards the morning sector. The conductivity-dominant region is further investigated using the extensive IRIS riometer and Tromsø magnetometer datasets with results showing a distinct seasonal dependence. The region of high current

  12. Substorm and Magnetosphere Characteristic Scales Inferred from the SuperMAG Auroral Electrojet Indices

    Science.gov (United States)

    Newell, P.; Gjerloev, J.

    2012-04-01

    A generalization of the traditional 12-station auroral electrojet index, AE, to include more than 100 magnetometer stations, SME, is an excellent predictor of global auroral power, even at high cadence (1-min). We use this index, and a data base of more than 53,000 substorms derived from it, covering 1980-2009, to investigate time and energy scales in the magnetosphere, during substorms and otherwise. We find, contrary to common opinion, that substorms do not have a preferred recurrence rate, but instead have two distinct dynamic regimes, each following a power law. The number of substorms recurring after a time Δt, N(Δt), varies as Δt -1.19 for short times (3 hr). Other evidence also shows these distinct regimes for the magnetosphere, including a break in the power law spectra for SME at about 3 h. The time between two consecutive substorms is only weakly correlated (r=0.18 for isolated and r=0.06 for recurrent) with the time until the next, suggesting quasi-periodicity is not common. However substorms do have a preferred size, with the typical peak SME magnitude reaching 400-600 nT, but with a mean of 656 nT, corresponding to a bit less than 40 GW auroral power. More surprisingly, another characteristic scale exists in the magnetosphere, namely a peak in the SME distribution around 61 nT, corresponding to about 5 GW precipitating auroral power. The dominant form of auroral precipitation is diffuse aurora, thus these values are properties of the magnetotail thermal electron distribution. The characteristic 5 GW value specifically represents a preferred minimum below which the magnetotail rarely drops. The magnetotail experiences continuous loss by precipitation, so the existence of a preferred minimum implies driving which rarely disappears altogether. Finally, the distribution of SME values across all times, in accordance with earlier work on AE, is best fit by the sum of two distributions, each normal in log(SME). The lower distribution (with a 40% weighting

  13. GPS phase scintillation during the geomagnetic storm of March 17, 2015: The relation to auroral electrojet currents

    DEFF Research Database (Denmark)

    Prikryl, Paul; Ghoddousi-Fard, Reza; Connors, Martin

    and magnetometers. GPS phase scintillation index is computed for L1 signal sampled at the rate of 50 Hz by specialized GPS scintillation receivers of the Expanded Canadian High Arctic Ionospheric Network (ECHAIN). To further extend the geographic coverage, the phasescintillation proxy index is obtained from......-enhanced plasma density (SED) and in the auroral oval during energetic particle precipitation events, substorms and pseudo-breakups in particular. In this paper we examine the relation to auroral electrojet currents observed by arrays of ground-based magnetometers and energetic particle precipitation observed...

  14. Forecasting of DST index from auroral electrojet indices using time-delay neural network + particle swarm optimization

    Science.gov (United States)

    Lazzús, J. A.; López-Caraballo, C. H.; Rojas, P.; Salfate, I.; Rivera, M.; Palma-Chilla, L.

    2016-05-01

    In this study, an artificial neural network was optimized with particle swarm algorithm and trained to predict the geomagmetic DST index one hour ahead using the past values of DST and auroral electrojet indices. The results show that the proposed neural network model can be properly trained for predicting of DST(t + 1) with acceptable accuracy, and that the geomagnetic indices used have influential effects on the good training and predicting capabilities of the chosen network.

  15. Numerical Modeling of Auroral and Equatorial Electrojet Behavior during Geomagnetic Storm Sequence on September 9-14, 2005

    Science.gov (United States)

    Klimenko, Maxim; Klimenko, Vladimir

    In Klimenko et al., 2006 the model of electric field and zonal current in the Earth's ionosphere has been presented. This model has been included into the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in WD IZMIRAN (Namgaladze et al., 1988). The modified GSM TIP model has allowed to describe more correctly the behavior of electric field and different ionospheric parameters at low latitudes, and also to investigate the behavior of auroral and equatorial electrojets. In the given research we present the calculation results of behavior of auroral and equatorial electrojets during geomagnetic storm sequence on September 9-14, 2005. The calculations have been executed with use of the modified GSM TIP model. At that the model input parameters, such as the potential difference through polar caps, field-aligned currents of second region and particle precipitation fluxes and energy were set as function of AE-and Kp-indices of geomagnetic activity according to different empirical models Feshchenko and Maltsev, 2003; Zhang and Paxton, 2008 and morphological representations Cheng et al., 2008. Furthermore, at the storm sudden commencement phase we taken into account the shift of field-aligned currents of the second region into the lower latitudes as by Sojka et al., 1994 and 30 min. time delay of variations of the field-aligned currents of the second region relative to the variations of the potential drop through polar caps. Also, we taken into account the ionospheric effects of solar flares, which were taken place during the considered period. The calculation results are analyzed according to known morphological representations about auroral and equatorial electrojet behavior during geomagnetic storms. This study is supported by RFBR grant 08-05-00274. References Cheng Z.W., Shi J.K., Zhang T.L., Dunlop M. and Liu Z.X. Relationship between FAC at plasma sheet boundary layers and AE index during storms from August to October

  16. Effects of substorm electrojet on declination along concurrent geomagnetic latitudes in the northern auroral zone

    Science.gov (United States)

    Edvardsen, Inge; Johnsen, Magnar G.; Løvhaug, Unni P.

    2016-10-01

    The geomagnetic field often experiences large fluctuations, especially at high latitudes in the auroral zones. We have found, using simulations, that there are significant differences in the substorm signature, in certain coordinate systems, as a function of longitude. This is confirmed by the analysis of real, measured data from comparable locations. Large geomagnetic fluctuations pose challenges for companies involved in resource exploitation since the Earth's magnetic field is used as the reference when navigating drilling equipment. It is widely known that geomagnetic activity increases with increasing latitude and that the largest fluctuations are caused by substorms. In the auroral zones, substorms are common phenomena, occurring almost every night. In principle, the magnitude of geomagnetic disturbances from two identical substorms along concurrent geomagnetic latitudes around the globe, at different local times, will be the same. However, the signature of a substorm will change as a function of geomagnetic longitude due to varying declination, dipole declination, and horizontal magnetic field along constant geomagnetic latitudes. To investigate and quantify this, we applied a simple substorm current wedge model in combination with a dipole representation of the Earth's magnetic field to simulate magnetic substorms of different morphologies and local times. The results of these simulations were compared to statistical data from observatories and are discussed in the context of resource exploitation in the Arctic. We also attempt to determine and quantify areas in the auroral zone where there is a potential for increased space weather challenges compared to other areas.

  17. Modulation of auroral electrojet currents using dual HF beams with ELF phase offset

    Science.gov (United States)

    Golkowski, M.; Cohen, M.; Moore, R. C.

    2012-12-01

    The modulation of naturally occuring ionospheric currents with high power radio waves in the high frequency (HF, 3-10 MHz) band is a well known technique for generation of extremely low frequency (ELF, 3-3000 Hz) and very low frequency (VLF, 3-30 kHz) waves. We use the heating facility of the High Frequency Active Auroral Research Program (HAARP) to investigate the effect of using dual HF beams with an ELF/VLF phase offset between the modulation waveforms. Experiments with offset HF beams confirm the model of independent ELF/VLF sources. Experiments with co-located HF beams exhibit interaction between the first and second harmonics of the modulated tones when square and sine wave modulation waveforms are employed. Using ELF/VLF phase offsets for co-loacted beams is also shown to be a potential diagnostic for the D-region ionospheric profile.

  18. Monitoring auroral electrojets with satellite data

    DEFF Research Database (Denmark)

    Vennerstrøm, Susanne; Moretto, T.

    2013-01-01

    satellites. The method is simple enough to be implemented for real-time monitoring, especially since it does not require the full vector field measurement. We demonstrate the method on 5 years of Challenging Minisatellite Payload (CHAMP) data and show how the monitoring depends on the local time...... of the satellite orbit and how it varies with local time and season in both hemispheres. Statistically, the strongest currents are observed in the predawn and predusk local time quadrants at latitudes that depend on the general magnetic activity level. We also show how the satellite-derived parameters relate......, this does not significantly affect the utility of the method for space weather applications even for satellites at substantially higher altitudes. The results for several individual magnetic storm periods demonstrate that large variability can exist in both the latitude and intensity of the currents during...

  19. IMF BY dependence of the extent of substorm westward electrojet

    Indian Academy of Sciences (India)

    T Arun; Ajay Dhar; K Emperumal; B M Pathan

    2005-04-01

    In this paper the duskward extension of the westward auroral electrojet is investigated for substorm intervals on the basis of magnetograms recorded at the Indian Antarctic station, Maitri. The database comprises three years from 1998-2000. Based on an initial study of the magnetograms, an arbitrary local time of 2030 MLT is fixed to define the early manifestation of the substorm westward electrojet. Using this criterion 12 substorms are identified and the possible causes examined. Many of these events are observed to be associated with a moderate to intense ring current.The hourly average of the GSM BY-component of the interplanetary magnetic field (IMF) for the hour preceding the substorm onset at Maitri is negative for most of the events. It is suggested that the azimuthal shift of the auroral electrojets in the southern hemisphere resulting from a negative BY-component of the IMF influences the extent of the substorm westward electrojet. This finding implies that the IMF may have a role in controlling the longitudinal extent of substorm occurrence.

  20. Calculating Auroral Oval Pattern by AE Index

    Institute of Scientific and Technical Information of China (English)

    CHEN Anqin; LI Jiawei; YANG Guanglin; WANG Jingsong

    2008-01-01

    The relationship between the auroral oval pattern, i.e., location, size, shape, and intensity, and the auroral electrojet activity index (AE index) is studied. It is found that the maximal auroral intensity is elliptically distributed, and the lengths of semimajor and semiminor axes are positively correlated to AE.The intensity along the normal of the auroral oval can be satisfyingly described by a Gaussian distribution,and the maximum and the full width at half maximum of the Gaussian distribution are both positively correlated to AE. Based on these statistical results, a series of experimental formulas as a function of AE are developed to calculate the location, size, shape, and intensity of the auroral oval. These formulas are validated by the auroral images released by SWPC/NOAA.

  1. The dawn and dusk electrojet response to substorm onset

    Directory of Open Access Journals (Sweden)

    E. Borälv

    Full Text Available We have investigated the time delay between substorm onset and related reactions in the dawn and dusk ionospheric electrojets, clearly separated from the nightside located substorm current wedge by several hours in MLT. We looked for substorm onsets occurring over Greenland, where the onset was identified by a LANL satellite and DMI magnetometers located on Greenland. With this setup the MARIA magnetometer network was located at dusk, monitoring the eastward electrojet, and the IMAGE chain at dawn, for the westward jet. In the first few minutes following substorm onset, sudden enhancements of the electrojets were identified by looking for rapid changes in magnetograms. These results show that the speed of information transfer between the region of onset and the dawn and dusk ionosphere is very high. A number of events where the reaction seemed to preceed the onset were explained by either unfavorable instrument locations, preventing proper onset timing, or by the inner magnetosphere's reaction to the Earthward fast flows from the near-Earth neutral line model. Case studies with ionospheric coherent (SuperDARN and incoherent (EISCAT radars have been performed to see whether a convection-induced electric field or enhanced conductivity is the main agent for the reactions in the electrojets. The results indicate an imposed electric field enhancement.

    Key words: Ionosphere (auroral ionosphere; electric fields and currents - Magnetospheric physics (storms and substorms

  2. Pulsed Artificial Electrojet Generation

    Science.gov (United States)

    Papadopoulos, K.

    2008-12-01

    Traditional techniques for generating low frequency signals in the ULF/ELF range (.1-100 Hz) and rely on ground based Horizontal Electric Dipole (HED) antennas. It is, furthermore, well known that a Vertical Electric Dipole (VED) is by more than 50 dB more efficient than a HED with the same dipole current moment. However, the prohibitively long length of VED antennas in the ELF/ULF range coupled with voltage limitations due to corona discharge in the atmosphere make them totally impracticable. In this paper we discuss a novel concept, inspired by the physics of the equatorial electrojet, that allows for the conversion of a ground based HED to a VED in the E-region of the equatorial ionosphere with current moment comparable to the driving HED. The paper focuses in locations near the dip-equator, where the earth's magnetic is in predominantly in the horizontal direction. The horizontal electric field associated with a pulsed HED drives a large Hall current in the ionospheric E-region, resulting in a vertical current. It is shown that the pulsed vertical current in the altitude range 80-130 km, driven by a horizontal electric field of, approximately, .1 mV/m at 100 km altitude, is of the order of kA. This results in a pulsed VED larger than 106 A-m. Such a pulsed VED will drive ELF/ULF pulses with amplitude in excess of .1 nT at a lateral range larger than few hundred kilometers. This is by three orders of magnitude larger than the one expected by a HED with comparable current moment. The paper will conclude with the description of a sneak-through technique that allows for creating pulsed electric fields in the ionosphere much larger than expected from steady state oscillatory HED antennas.

  3. Investigating the auroral electrojets with low altitude polar orbiting satellites

    DEFF Research Database (Denmark)

    Moretto, T.; Olsen, Nils; Ritter, P.

    2002-01-01

    Three geomagnetic satellite missions currently provide high precision magnetic field measurements from low altitude polar orbiting spacecraft. We demonstrate how these data can be used to determine the intensity and location of the horizontal currents that flow in the ionosphere, predominantly...

  4. The effect of multiple scattering on the aspect sensitivity and polarization of radio auroral echoes

    Energy Technology Data Exchange (ETDEWEB)

    Donovan, E.F.; Moorcroft, D.R. (Western Ontario, University, London (Canada))

    1992-04-01

    A Monte Carlo model of radio wave scattering in the auroral electrojet has been developed to investigate multiple scattering of radio auroral echoes. Using this model, predictions of the aspect angle behavior of first-, second-, and third-order scattered power have been made. The results indicate that multiple scattering may be an important effect for VHF radars which observe the auroral E region at large magnetic aspect angles. The model shows that linearly polarized radio waves can become depolarized because of multiple scattering if the radio transmitter is horizontally polarized but not if the radio transmitter is vertically polarized. 52 refs.

  5. A new technique for determining Substorm Onsets and Phases from Indices of the Electrojet (SOPHIE)

    CERN Document Server

    Forsyth, C; Coxon, J C; Freeman, M P; Jackman, C M; Gjerloev, J; Fazakerley, A N

    2016-01-01

    We present a new quantitative technique that determines the times and durations of substorm expansion and recovery phases and possible growth phases based on percentiles of the rate of change of auroral electrojet indices. By being able to prescribe different percentile values, we can determine the onset and duration of substorm phases for smaller or larger variations of the auroral index or indeed any auroral zone ground-based magnetometer data. We apply this technique to the SuperMAG AL (SML) index and compare our expansion phase onset times with previous lists of substorm onsets. We find that more than 50% of events in previous lists occur within 20 min of our identified onsets. We also present a comparison of superposed epoch analyses of SML based on our onsets identified by our technique and existing onset lists and find that the general characteristics of the substorm bay are comparable. By prescribing user-defined thresholds, this automated, quantitative technique represents an improvement over any vis...

  6. Investigating the polar electrojet using Swarm satellite magnetic data

    DEFF Research Database (Denmark)

    Aakjær, Cecilie Drost; Olsen, Nils; Finlay, Chris

    The aim of this study is to investigate the magnetic perturbations caused by the polar electrojets, which are described by means of a model consisting of a series of infinite line currents placed at the height of the ionosphere along QD latitudes. The method is applied to Swarm magnetic scalar pe...... of the polar electrojets as well as their temporal evolution. In addition, applying the method to data taken by the Swarm satellites Alpha and Beta allows investigating longitudinal differences of the electrojets.......The aim of this study is to investigate the magnetic perturbations caused by the polar electrojets, which are described by means of a model consisting of a series of infinite line currents placed at the height of the ionosphere along QD latitudes. The method is applied to Swarm magnetic scalar...

  7. Meridional equatorial electrojet current in the American sector

    Directory of Open Access Journals (Sweden)

    R. G. Rastogi

    Full Text Available Huancayo is the only equatorial electrojet station where the daytime increase of horizontal geomagnetic field (H is associated with a simultaneous increase of eastward geomagnetic field (Y. It is shown that during the counter electrojet period when ∆H is negative, ∆Y also becomes negative. Thus, the diurnal variation of ∆Y at equatorial latitudes is suggested to be a constituent part of the equatorial electrojet current system. Solar flares are known to increase the H field at an equatorial station during normal electrojet conditions (nej. At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter electrojet periods (cej, a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the equatorial electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.

    Key words. Geomagnetism and paleomagnetism (dynamo theories · Ionosphere (equatorial ionosphere; ionosphere disturbances

  8. Danish auroral science history

    Science.gov (United States)

    Stauning, P.

    2011-01-01

    Danish auroral science history begins with the early auroral observations made by the Danish astronomer Tycho Brahe during the years from 1582 to 1601 preceding the Maunder minimum in solar activity. Included are also the brilliant observations made by another astronomer, Ole Rømer, from Copenhagen in 1707, as well as the early auroral observations made from Greenland by missionaries during the 18th and 19th centuries. The relations between auroras and geomagnetic variations were analysed by H. C. Ørsted, who also played a vital role in the development of Danish meteorology that came to include comprehensive auroral observations from Denmark, Iceland and Greenland as well as auroral and geomagnetic research. The very important auroral investigations made by Sophus Tromholt are outlined. His analysis from 1880 of auroral observations from Greenland prepared for the significant contributions from the Danish Meteorological Institute, DMI, (founded in 1872) to the first International Polar Year 1882/83, where an expedition headed by Adam Paulsen was sent to Greenland to conduct auroral and geomagnetic observations. Paulsen's analyses of the collected data gave many important results but also raised many new questions that gave rise to auroral expeditions to Iceland in 1899 to 1900 and to Finland in 1900 to 1901. Among the results from these expeditions were 26 unique paintings of the auroras made by the artist painter, Harald Moltke. The expedition to Finland was headed by Dan la Cour, who later as director of the DMI came to be in charge of the comprehensive international geomagnetic and auroral observations made during the Second International Polar Year in 1932/33. Finally, the article describes the important investigations made by Knud Lassen during, among others, the International Geophysical Year 1957/58 and during the International Quiet Sun Year (IQSY) in 1964/65. With his leadership the auroral and geomagnetic research at DMI reached a high international

  9. Danish auroral science history

    Directory of Open Access Journals (Sweden)

    P. Stauning

    2011-01-01

    Full Text Available Danish auroral science history begins with the early auroral observations made by the Danish astronomer Tycho Brahe during the years from 1582 to 1601 preceding the Maunder minimum in solar activity. Included are also the brilliant observations made by another astronomer, Ole Rømer, from Copenhagen in 1707, as well as the early auroral observations made from Greenland by missionaries during the 18th and 19th centuries. The relations between auroras and geomagnetic variations were analysed by H. C. Ørsted, who also played a vital role in the development of Danish meteorology that came to include comprehensive auroral observations from Denmark, Iceland and Greenland as well as auroral and geomagnetic research. The very important auroral investigations made by Sophus Tromholt are outlined. His analysis from 1880 of auroral observations from Greenland prepared for the significant contributions from the Danish Meteorological Institute, DMI, (founded in 1872 to the first International Polar Year 1882/83, where an expedition headed by Adam Paulsen was sent to Greenland to conduct auroral and geomagnetic observations. Paulsen's analyses of the collected data gave many important results but also raised many new questions that gave rise to auroral expeditions to Iceland in 1899 to 1900 and to Finland in 1900 to 1901. Among the results from these expeditions were 26 unique paintings of the auroras made by the artist painter, Harald Moltke. The expedition to Finland was headed by Dan la Cour, who later as director of the DMI came to be in charge of the comprehensive international geomagnetic and auroral observations made during the Second International Polar Year in 1932/33. Finally, the article describes the important investigations made by Knud Lassen during, among others, the International Geophysical Year 1957/58 and during the International Quiet Sun Year (IQSY in 1964/65. With his leadership the auroral and geomagnetic research at DMI reached a high

  10. Equatorial electrojet in east Brazil longitudes

    Indian Academy of Sciences (India)

    R G Rastogi; H Chandra; K Yumuto

    2010-08-01

    This paper describes the morphology of the equatorial electrojet (EEJ) along 45°W longitude in east Brazil, where the ground magnetic (dip) equator is associated with the largest declination in the world. Daily range of the horizontal field ( ), as expected, was largest at the station in the chain closest to the dip equator, Sao Luiz (inclination −0.25°S). was largest positive at Eusebio (inclination 9.34°S) and largest negative at Belem (inclination 7.06°N); both near the fringe of EEJ belt. at Sao Luiz during the daytime was unexpectedly large negative in-spite of a small dip and also located south of the dip equator where should be positive. Center of EEJ was found to be shifted southward of the dip equator by about 1° in latitude. During southern summer, started decreasing from 00 h and reached a minimum value in the afternoon, an abnormal feature not discussed for any station so far. The mid-day value of the direction of vector was 22°-24°W compared to the declination of 19°–21°W in the region.

  11. Generation of Electrojets in Weakly Ionized Plasmas through a Collisional Dynamo

    CERN Document Server

    Dimant, Yakov S; Fletcher, Alex C

    2016-01-01

    Intense electric currents called electrojets occur in weakly ionized magnetized plasmas. An example occurs in the Earth's ionosphere near the magnetic equator where neutral winds drive the plasma across the geomagnetic field. Similar processes take place in the Solar chromosphere and MHD generators. This letter argues that not all convective neutral flows generate electrojets and it introduces the corresponding universal criterion for electrojet formation, $\

  12. The equatorial electrojet current modelling from SWARM satellite data

    Science.gov (United States)

    Benaissa, Mahfoud

    2016-07-01

    Equatorial ElectroJet (EEJ) is an intense eastward electric current circulating in the ionospheric magnetic equator band between 100 and 130 km of altitude in E region. These currents vary by day, by season, by solar activity, and also with the main magnetic field of internal origin. The irregularity of the ionosphere has a major impact on the performance of communication systems and navigation (GPS), industry.... Then it becomes necessary study the characteristics of EEJ. In this paper, we present a study of the equatorial electrojet (EEJ) phenomenon along one year (2014) period. In addition, the satellite data used in this study are obtained with SWARM satellite scalar magnetometer data respecting magnetically quiet days with KP < 2. In this paper, we process to separate and extract the electrojet intensity signal from other recorded signal-sources interfering with the main signal and reduce considerably the signal to noise ratio during the SWARM measurements. This pre-processing step allows removing all external contributions in regard to EEJ intensity value. Key words: Ionosphere (Equatorial ionosphere; Electric fields and currents; Equatorial electrojet (EEJ)); SWARM.

  13. Ionospheric conductances and currents of a morning sector auroral arc from Swarm-A electric and magnetic field measurements

    Science.gov (United States)

    Juusola, L.; Archer, W. E.; Kauristie, K.; Burchill, J. K.; Vanhamäki, H.; Aikio, A. T.

    2016-11-01

    We show the first ionospheric Hall and Pedersen conductances derived from Swarm magnetic and electric field measurements during a crossing of a morning sector auroral arc. Only Swarm-A was used, with assumptions of negligible azimuthal gradients and vanishing eastward electric field. We find upward field-aligned current, enhanced Hall and Pedersen conductances, and relatively weak electric field coincident with the arc. Poleward of the arc, the field-aligned current was downward, conductances lower, and the electric field enhanced. The arc was embedded in a westward electrojet, immediately equatorward of the peak current density. The equatorward portion of the electrojet could thus be considered conductance dominant and the poleward portion electric field dominant. Although the electric field measured by Swarm was intense, resulting in conductances lower than those typically reported, comparable electric fields have been observed earlier. These results demonstrate how Swarm data can significantly contribute to our understanding of the ionospheric electrodynamics.

  14. Possible evidence for partial demagnetization of electrons in the auroral E-region plasma during electron gas heating

    Directory of Open Access Journals (Sweden)

    C. Haldoupis

    Full Text Available A previous study, based on incoherent and coherent radar measurements, suggested that during auroral E-region electron heating conditions, the electron flow in the auroral electrojet undergoes a systematic counterclockwise rotation of several degrees relative to the E×B direction. The observational evidence is re-examined here in the light of theoretical predictions concerning E-region electron demagnetization caused by enhanced anomalous cross-field diffusion during strongly-driven Farley-Buneman instability. It is shown that the observations are in good agreement with this theory. This apparently endorses the concept of wave-induced diffusion and anomalous electron collision frequency, and consequently electron demagnetization, under circumstances of strong heating of the electron gas in the auroral electrojet plasma. We recognize, however, that the evidence for electron demagnetization presented in this report cannot be regarded as definitive because it is based on a limited set of data. More experimental research in this direction is thus needed.

  15. The relationship between VHF radar auroral backscatter amplitude and Doppler velocity: a statistical study

    Directory of Open Access Journals (Sweden)

    B. A. Shand

    Full Text Available A statistical investigation of the relationship between VHF radar auroral backscatter intensity and Doppler velocity has been undertaken with data collected from 8 years operation of the Wick site of the Sweden And Britain Radar-auroral Experiment (SABRE. The results indicate three different regimes within the statistical data set; firstly, for Doppler velocities <200 m s–1, the backscatter intensity (measured in decibels remains relatively constant. Secondly, a linear relationship is observed between the backscatter intensity (in decibels and Doppler velocity for velocities between 200 m s–1 and 700 m s–1. At velocities greater than 700 m s–1 the backscatter intensity saturates at a maximum value as the Doppler velocity increases. There are three possible geophysical mechanisms for the saturation in the backscatter intensity at high phase speeds: a saturation in the irregularity turbulence level, a maximisation of the scattering volume, and a modification of the local ambient electron density. There is also a difference in the dependence of the backscatter intensity on Doppler velocity for the flow towards and away from the radar. The results for flow towards the radar exhibit a consistent relationship between backscatter intensity and measured velocities throughout the solar cycle. For flow away from the radar, however, the relationship between backscatter intensity and Doppler velocity varies during the solar cycle. The geometry of the SABRE system ensures that flow towards the radar is predominantly associated with the eastward electrojet, and flow away is associated with the westward electrojet. The difference in the backscatter intensity variation as a function of Doppler velocity is attributed to asymmetries between the eastward and westward electrojets and the geophysical parameters controlling the backscatter amplitude.

  16. Far ultraviolet auroral imager

    Institute of Scientific and Technical Information of China (English)

    FU LiPing; WANG YongMei; WANG YingJian; ZHANG ZhongMou; LU JianGong

    2009-01-01

    Reviewing the technology development of imaging the global FUV auroral morphology,we introduce a space-based FUV auroral imager prototype developed by the Center for Space Science and Applied Research(CSSAR).It is designed to obtain continuous observations on the temporal and spatial morphology of the aurora which occupies highly elliptical high-altitude near-polar orbits.Primarily composed of a telescope system,image intensifier system,CCD,and collection and control system,the instrument works in the spectral region from 140-190 nm in the field of view 25°×25°,and the spatial resolution is better than 0.1°.

  17. Far ultraviolet auroral imager

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Reviewing the technology development of imaging the global FUV auroral morphology,we introduce a space-based FUV auroral imager prototype developed by the Center for Space Science and Applied Research(CSSAR).It is designed to obtain continuous observations on the temporal and spatial morphology of the aurora which occupies highly elliptical high-altitude near-polar orbits.Primarily composed of a telescope system,image intensifier system,CCD,and collection and control system,the instrument works in the spectral region from 140―190 nm in the field of view 25°×25°,and the spatial resolution is better than 0.1°.

  18. The field of the equatorial electrojet from CHAMP data

    Directory of Open Access Journals (Sweden)

    J.-L. Le Mouël

    2006-03-01

    Full Text Available We apply a simple linear transform, the along-track second derivative, to four years of scalar and vectorial data from the CHAMP satellite. This transform, reminiscent of techniques used in the interpretation of aeromagnetic surveys, is applied either to the geocentric spherical components of the field or to its intensity. After averaging in time and space, we first produce a map of the crustal field, then maps of the equatorial electrojet field at all local times and all universal times. The seasonal variation of the electrojet, its evolution with the solar cycle, and the effect of geomagnetic activity are discussed. The variation of the electrojet with longitude, an intriguing feature revealed by satellite data, is described in some detail, and it is shown that this longitude dependance is stable in time. The existence of a counterelectrojet in the morning, everywhere except over the Pacific Ocean, is established. The signatures of closure electric currents and of interhemispheric currents are also evidenced.

  19. Landau damping of auroral hiss

    Science.gov (United States)

    Morgan, D. D.; Gurnett, D. A.; Menietti, J. D.; Winningham, J. D.; Burch, J. L.

    1994-01-01

    Auroral hiss is observed to propagate over distances comparable to an Earth radius from its source in the auroral oval. The role of Landau damping is investigated for upward propagating auroral hiss. By using a ray tracing code and a simplified model of the distribution function, the effect of Landau damping is calculated for auroral hiss propagation through the environment around the auroral oval. Landau damping is found to be the likely mechanism for explaining some of the one-sided auroral hiss funnels observed by Dynamics Explorer 1. It is also found that Landau damping puts a lower limit on the wavelength of auroral hiss. Poleward of the auroral oval, Landau damping is found in a typical case to limit omega/k(sub parallel) to values of 3.4 x 10(exp 4) km/s or greater, corresponding to resonance energies of 3.2 keV or greater and wavelengths of 2 km or greater. For equatorward propagation, omega/k(sub parallel) is limited to values greater than 6.8 x 10(exp 4) km/s, corresponding to resonance energies greater than 13 keV and wavelengths greater than 3 km. Independent estimates based on measured ratios of the magnetic to electric field intensity also show that omega/k(sub parallel) corresponds to resonance energies greater than 1 keV and wavelengths greater than 1 km. These results lead to the difficulty that upgoing electron beams sufficiently energetic to directly generate auroral hiss of the inferred wavelength are not usually observed. A partial transmission mechanism utilizing density discontinuities oblique to the magnetic field is proposed for converting auroral hiss to wavelengths long enough to avoid damping of the wave over long distances. Numerous reflections of the wave in an upwardly flared density cavity could convert waves to significantly increased wavelengths and resonance velocities.

  20. The Wave-Like Auroral Structure around Auroral Expansion Onset

    Institute of Scientific and Technical Information of China (English)

    TANG Chao-Ling

    2011-01-01

    We present the direct connection between the wave-like auroral structure around the time of auroral expansion onset and the ballooning mode waves in the near-Earth magnetotail. Based on the NASA mission time history of events and macroscale interactions during substorms (THEMIS) ground-based all-sky imagers, we show that around the time of auroral expansion onset, a wave-like auroral structure first has four luminosity peaks separated by 2-3° magnetic longitude (MLON). Subsequently, the wave-like structure propagates in the azimuthal direction and an overall bright arc spans approximately 1 h magnetic local time. The wavelength is estimated to be 120-180 km. Finally, a noticeable poleward auroral expansion is observed. The ballooning mode waves are identified by two THEMIS probes in the near-Earth magnetotail. The observed wavelength of the ballooning mode waves is approximately equal to the order of the ion Larmor radius. The wavelength of 1500 3000 km in the near-Earth magnetotail is comparable with the wave-like auroral structure estimate. This study suggests that the ballooning mode waves might play a crucial role in auroral expansion onset, corresponding to the wave-like auroral structure in this study.%We present the direct connection between the wave-like auroral structure around the time of auroral expansion onset and the ballooning mode waves in the near-Earth magnetotail.Based on the NASA mission time history of events and macroscale interactions during substorms (THEMIS) ground-based all-sky imagers,we show that around the tirne of auroral expansion onset,a wave-like auroral structure first has four luminosity peaks separated by 2-3° magnetic longitude (MLON).Subsequently,the wave-like structure propagates in the azimuthal direction and an overall bright arc spans approximately 1 h magnetic local time.The wavelength is estimated to be 120-180 km.Finally,a noticeable poleward auroral expansion is observed.The ballooning mode waves are identified by two

  1. Coordinated ground and space measurements of an auroral surge over South Pole

    Energy Technology Data Exchange (ETDEWEB)

    Rosenberg, T.J.; Detrick, D.L.; Mizera, P.F.; Gorney, D.J.; Berkey, F.T.; Eather, R.H.; Lanzerotti, L.J.

    1987-10-01

    Coincident ground-based and satellite observations are presented of a premidnight auroral surge over Amundsen-Scott South Pole station. The set of near-simultaneous measurements provides an excellent opportunity to gain a more quantitative understanding of the nature of premidnight substorm activity at high geomagnetic latitudes. The surge produced a rapid onset of cosmic radio noise absorption at the station. On the polar-orbiting DMSP F6 spacecraft, intense X ray emissions with E>2 keV energy were imaged 1/sup 0/ to 2/sup 0/ magnetically equatorward of South Pole approximately 1 min prior to the peak of the absorption event. The spectrum of precipitating electrons determined from the X ray measurements could be characterized by an e-folding energy of approx.11 keV and is found to be adequate to account for the cosmic noise absorption and maximum auroral luminosity recorded at South Pole. Photometer, all-sky camera, riometer, and magnetometer data are used to estimate the velocity of motion and spatial extent of the auroral precipitation and the ionospheric currents associated with the surge. The electron precipitation region is deduced to have a latitudinal scale size of <100 km and to move poleward with a speed of approx.1--2 km/s coincident with the movement of a westward electrojet.

  2. Auroral interactions with ISSA

    Science.gov (United States)

    Purvis, Carolyn K.; Snyder, David B.; Jongeward, Gary A.

    1994-01-01

    Due to its high inclination orbit, International Space Station Alpha (ISSA) will occasionally experience surface charging by the high energy electrons of the auroral environment. This study looks at the frequency of these occurrences and recapitulates a charging model. ISSA should expect about 80 auoral encounters annually. If the plasma contactor is not run continuously, the vehicle may charge several hundred volts. Charge storage on standard space station coatings should not be a problem, but care must be taken that materials are not introduced inadvertently that cannot bleed off accumulated charge in a reasonable time. A conductivity requirement may be used to ensure surface materials do not charge to high voltages, or store charge for long periods of time.

  3. Auroral Spatial Structures Probe Project

    Data.gov (United States)

    National Aeronautics and Space Administration —    Methodology Fly a high altitude sounding rocket with multiple sub-payloads to measure electric and magnetic fields during an auroral event. Use...

  4. New observations of ionospheric instabilities in the equatorial electrojet

    Science.gov (United States)

    Alken, P.; Maus, S.

    2009-12-01

    The equatorial electrojet (EEJ) is an intense current system flowing along the magnetic equator in the ionospheric E-region on the day-side. Early attempts to model the EEJ found that ionospheric instabilities led to significant changes in the current which had to be accounted for. Early modelers used ad-hoc empirical correction factors in the relevant ionospheric parameters to attempt to account for instability effects. Modern EEJ models continue to use these correction factors, which are still not well understood theoretically. In the last decade, a wealth of new data has been recorded by both satellites and ground radars which allows us to revisit the issue of modeling these ionospheric instabilities. In this work, we use radar and magnetic field measurements at Jicamarca in addition to magnetometer measurements from the CHAMP satellite to study the effects of ionospheric instabilities on the EEJ. We find that the effects of ionospheric instabilities lead to non-linear behavior between the eastward electric field strength and the resulting electrojet current. As predicted, the ratio of current to electric field is highest for westward and weak eastward electric fields, and the ratio decreases with stronger eastward electric fields. Quantifying this non-linearity should help improve the accuracy of equatorial electrodynamic models.

  5. Equatorial magnetospheric particles and auroral precipitations

    Science.gov (United States)

    McIlwain, C. E.

    The injection boundary beyond which fresh hot plasma appears each magnetospheric substorm is generalized and extended to circle the Earth. The concept of an auroral shell representing the inner limit of active auroral processes is introduced. It is proposed that at low altitudes, this shell marks the equatorward edge of the auroral ovals, and that at high altitudes, it marks the injection boundary. The auroral ring is defined as the intersection of the auroral shell with the magnetic equator. A simple equation for computing the expected location of the auroral ring as a function of local time and magnetic disturbance level is obtained. Tests indicate that the model is valid and reasonably accurate.

  6. Characteristics of equatorial electrojet derived from Swarm satellites

    Science.gov (United States)

    Thomas, Neethal; Vichare, Geeta; Sinha, A. K.

    2017-03-01

    The vector magnetic field measurements from three satellite constellation, Swarm mission (Alpha 'Swarm-A', Bravo 'Swarm-B', and Charlie 'Swarm-C') during the quiet days (daily ∑Kp ⩽ 10) of the years 2014-2015 are used to study the characteristic features of equatorial electrojet (EEJ). A program is developed to identify the EEJ signature in the X (northward) component of the magnetic field recorded by the satellite. An empirical model is fitted into the observed EEJ signatures separately for both the hemispheres, to obtain the parameters of electrojet current such as peak current density, total eastward current, the width of EEJ, position of the electrojet axis, etc. The magnetic field signatures of EEJ at different altitudes are then estimated. Swarm B and C are orbiting at different heights (separation ∼50 km) and during the month of April 2014, both the satellites were moving almost simultaneously over nearby longitudes. Therefore, we used those satellite passes to validate the methodology used in the present study. The magnetic field estimates at the location of Swarm-C obtained using the observations of Swarm B are compared with the actual observations of Swarm-C. A good correlation between the actual and the computed values (correlation coefficient = 0.98) authenticates the method of analysis. The altitudinal variation of the amplitude and the width of the EEJ signatures are also depicted. The ratio of the total eastward flowing forward to westward return currents is found to vary between 0.1 and 1.0. The forward and return current values in the northern hemisphere are found to be ∼0.5 to 2 times of those in the southern hemisphere, thereby indicating the hemispheric asymmetry. The latitudinal extents of the forward and return currents are found to have longitudinal dependence similar to that of the amplitude and the width of EEJ showing four peak structures. Local time dependence of EEJ parameters has also been investigated. In general, the results

  7. Characteristics of Extreme Auroral Charging Events

    Science.gov (United States)

    Minow, Joseph I.; Willis, Emily; Parker, Linda Neergaard

    2014-01-01

    Today’s presentation describes preliminary results from a study of extreme auroral charging in low Earth orbit. Goal of study is to document characteristics of auroral charging events of importance to spacecraft design, operations, and anomaly investigations.

  8. Altitude and latitude dependence of the equatorial electrojet

    Science.gov (United States)

    Singh, A.; Cole, K. D.

    1988-07-01

    A self-consistent and high-resolution dynamo model is used to investigate the effects of day-to-day or seasonal variation of altitude and latitude profiles of the E-plasma density in the equatorial ionosphere on equatorial electrojet (EEJ) structure. Variations in the E-layer peak altitude and amplitude are shown to significantly affect EEJ structure. The results indicate that, for any shape, the EEJ peak appears at or below the E-layer peak altitude. Distinct double peaks occur in the EEJ structure if the E-layer peak is above 105 km or if the gradient is large. The effect of the latitudinal variation of the integrated conductivities of ionospheric field lines upon the amplitude and altitude of the EEJ peak is discussed.

  9. Combined radar observations of equatorial electrojet irregularities at Jicamarca

    Directory of Open Access Journals (Sweden)

    D. L. Hysell

    2007-03-01

    Full Text Available Daytime equatorial electrojet plasma irregularities were investigated using five distinct radar diagnostics at Jicamarca including range-time-intensity (RTI mapping, Faraday rotation, radar imaging, oblique scattering, and multiple-frequency scattering using the new AMISR prototype UHF radar. Data suggest the existence of plasma density striations separated by 3–5 km and propagating slowly downward. The striations may be caused by neutral atmospheric turbulence, and a possible scenario for their formation is discussed. The Doppler shifts of type 1 echoes observed at VHF and UHF frequencies are compared and interpreted in light of a model of Farley Buneman waves based on kinetic ions and fluid electrons with thermal effects included. Finally, the up-down and east-west asymmetries evident in the radar observations are described and quantified.

  10. The enigma of auroral spirals

    Science.gov (United States)

    Haerendel, G.

    One of the most spectacular forms that the aurora borealis can assume is the large-scale spiral Spirals are dominantly observed along the poleward boundary of the auroral oval during active periods Two concepts have been pursued in explaining their origin and in particular the counterclockwise sense of rotation of the luminous structures when viewed along the magnetic field direction An essentially magnetostatic theory following Hallinan 1976 attributes the spiral pattern to the twisting of field-lines caused by a centrally located upward field-aligned current According to Oguti 1981 and followers a clockwise rotation of the plasma flow produces the anticlockwise structure There are observations seemingly confirming or contradicting either theory In this paper it is argued that both concepts are insufficient in that only parts of the underlying physics are considered Besides field-aligned currents and plasma flow one has to take into at least two further aspects The ionospheric conductivity modified by particle precipitation has an impact on the magnetospheric plasma dynamics Furthermore auroral arcs are not fixed entities subject to distortions by plasma flows or twisted field-lines but sites of transient releases of energy We suggest that auroral spirals are ports of entry or exit of plasma into or out of the auroral oval This way it can be understood why a clockwise plasma flow can create an anticlockwise luminous pattern

  11. Equatorial electrojet in the south Atlantic anomaly region

    Indian Academy of Sciences (India)

    R G Rastogi; H Chandra; N B Trivedi; V Doumbia

    2011-04-01

    Features of the equatorial electrojet are studied at Sao Luiz (2.6°S, 44.2°W, inclination −0.25°) in eastern Brazil and Sikasso (11.3°N, 5.7°W, inclination 0.1°) in the western African sector. The stations are situated on either side of the lowest magnetic field intensity in the region of rapid changes in the declination. The daily variations of X at the two stations are almost similar with the peak around noon with maximum values during equinoxes and minimum values during J-solstices. Daily variations of Y differ with the maximum deviation of about −35 nT around noon at Sao Luiz and much smaller value of about −10 nT around 14 h LT for Sikasso. The direction of the vector varies from 15°W of north at 08 h to more than 30°W of north at 17 h for Sao Luiz and from 14°E of north to 25°W of north at 18 h for Sikasso. The plot of the deviations in X and Y at different hours for the two stations shows the points along narrow ellipses with major axis aligned along 22°W of north for Sao Luiz and along 3°W of north for Sikasso as compared to declination of 20°W for Sao Luiz and 6°W for Sikasso. The deviations in X at the two stations are fairly well correlated.

  12. Reconstruction of Fine Scale Auroral Dynamics

    CERN Document Server

    Hirsch, Michael; Zettergren, Matthew; Dahlgren, Hanna; Goenka, Chhavi; Akbari, Hassanali

    2015-01-01

    We present a feasibility study for a high frame rate, short baseline auroral tomographic imaging system useful for estimating parametric variations in the precipitating electron number flux spectrum of dynamic auroral events. Of particular interest are auroral substorms, characterized by spatial variations of order 100 m and temporal variations of order 10 ms. These scales are thought to be produced by dispersive Alfv\\'en waves in the near-Earth magnetosphere. The auroral tomography system characterized in this paper reconstructs the auroral volume emission rate to estimate the characteristic energy and location in the direction perpendicular to the geomagnetic field of peak electron precipitation flux using a distributed network of precisely synchronized ground-based cameras. As the observing baseline decreases, the tomographic inverse problem becomes highly ill-conditioned; as the sampling rate increases, the signal-to-noise ratio degrades and synchronization requirements become increasingly critical. Our a...

  13. Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data

    DEFF Research Database (Denmark)

    Aakjær, Cecilie Drost; Olsen, Nils; Finlay, Chris

    2016-01-01

    We determine the strength and location of the ionospheric currents responsible for the polar electrojets from magnetic data collected by the Swarm satellite constellation on an orbit-by-orbit basis. The ionospheric currents are modelled using a simple, yet robust, method by a series of line curre...

  14. Advanced Stellar Compass Summary for the Auroral Lites mission

    DEFF Research Database (Denmark)

    Jørgensen, John Leif

    1998-01-01

    This document provides technical and managerial information about the Advanced Stellar Compass and its possible use in the Auroral Lites Project.The Auroral Lites is a NASA project.......This document provides technical and managerial information about the Advanced Stellar Compass and its possible use in the Auroral Lites Project.The Auroral Lites is a NASA project....

  15. Auroral effects in the D region of the ionosphere. [interactions between auroral particles and electromagnetic fields

    Science.gov (United States)

    Akasofu, S. I.

    1974-01-01

    Physical phenomena associated with the interaction between auroral particles and electromagnetic fields, auroral energy flow, and the propagation of auroral effects to low altitudes are discussed in detail. It is concluded that energy deposition of soft auroral X-rays would be negligible at stratospheric altitudes. New data from incoherent backscatter measurements of neutral winds in the auroral region indicate a lack of correlation between stratospheric winds and winds in the auroral ionosphere. Magnetograms are used to show that sector boundary crossings with a time scale of approximately one hour (as opposed to the sector structure itself with a time scale of several days) do not couple effectively with the magnetosphere and are not significant energy inputs to it.

  16. Spectral analysis of auroral geomagnetic activity during various solar cycles between 1960 and 2014

    Science.gov (United States)

    Kotzé, Pieter Benjamin

    2016-12-01

    In this paper we use wavelets and Lomb-Scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the AE (auroral electrojet) index during various phases of different solar cycles between 1960 and 2014. Previous investigations have revealed that the solar minimum of cycles 23-24 exhibited strong 13.5- and 9.0-day recurrence in geomagnetic data in comparison to the usual dominant 27.0-day synodic solar rotation period. Daily mean AE indices are utilized to show how several harmonics of the 27-day recurrent period change during every solar cycle subject to a 95 % confidence rule by performing a wavelet analysis of each individual year's AE indices. Results show that particularly during the solar minimum of 23-24 during 2008 the 27-day period is no longer detectable above the 95 % confidence level. During this interval geomagnetic activity is now dominated by the second (13.5-day) and third (9.0-day) harmonics. A Pearson correlation analysis between AE and various spherical harmonic coefficients describing the solar magnetic field during each Carrington rotation period confirms that the solar dynamo has been dominated by an unusual combination of sectorial harmonic structure during 23-24, which can be responsible for the observed anomalously low solar activity. These findings clearly show that, during the unusual low-activity interval of 2008, auroral geomagnetic activity was predominantly driven by high-speed solar wind streams originating from multiple low-latitude coronal holes distributed at regular solar longitude intervals.

  17. Comment: An Apparent Controversy in Auroral Physics

    Science.gov (United States)

    Haerendel, Gerhard

    2007-03-01

    In his article ``A turning point in auroral physics,'' Bryant argued against what he called the `standard' theory of auroral acceleration, according to which the electrons ``gain their energy from static electric fields,'' and offered wave acceleration as an alternative. Because of the importance of the process, not only for the aurora borealis but also for other cosmic plasmas, a clarification of this apparent controversy seems to be in place.

  18. Counter electrojet features in the Brazilian sector: simultaneous observation by radar, digital sounder and magnetometers

    Directory of Open Access Journals (Sweden)

    C. M. Denardini

    2009-04-01

    Full Text Available In the present work we show new results regarding equatorial counter electrojet (CEJ events in the Brazilian sector, based on the RESCO radar, two set of fluxgate magnetometer systems and a digital sounder. RESCO radar is a 50 MHz backscatter coherent radar installed in 1998 at São Luís (SLZ, 2.33° S, 44.60° W, an equatorial site. The Digital sounder routinely monitors the electron density profile at the radar site. The magnetometer systems are fluxgate-type installed at SLZ and Eusébio (EUS, 03.89° S, 38.44° W. From the difference between the horizontal component of magnetic field at SLZ station and the same component at EUS (EEJ ground strength several cases of westward morning electrojet and its normal inversion to the eastward equatorial electrojet (EEJ have been observed. Also, the EEJ ground strength has shown some cases of CEJ events, which been detected with the RESCO radar too. Detection of these events were investigated with respect to their time and height of occurrence, correlation with sporadic E (Es layers at the same time, and their spectral characteristics as well as the radar echo power intensity.

  19. Multiscale equatorial electrojet turbulence: Energy conservation, coupling, and cascades in a baseline 2-D fluid model

    Science.gov (United States)

    Hassan, Ehab; Hatch, D. R.; Morrison, P. J.; Horton, W.

    2016-09-01

    Progress in understanding the coupling between plasma instabilities in the equatorial electrojet based on a unified fluid model is reported. Simulations with parameters set to various ionospheric background conditions revealed properties of the gradient-drift and Farley-Buneman instabilities. Notably, sharper density gradients increase linear growth rates at all scales, whereas variations in cross-field E × B drift velocity only affect small-scale instabilities. A formalism defining turbulent fluctuation energy for the system is introduced, and the turbulence is analyzed within this framework. This exercise serves as a useful verification test of the numerical simulations and also elucidates the physics underlying the ionospheric turbulence. Various physical mechanisms involved in the energetics are categorized as sources, sinks, nonlinear transfer, and cross-field coupling. The physics of the nonlinear transfer terms is studied to identify their roles in producing energy cascades, which explain the generation of small-scale structures that are stable in the linear regime. The theory of two-step energy cascading to generate the 3 m plasma irregularities in the equatorial electrojet is verified for the first time in the fluid regime. In addition, the nonlinearity of the system allows the possibility of an inverse energy cascade, potentially responsible for generating large-scale plasma structures at the top of the electrojet as found in different rocket and radar observations.

  20. Statistical study of auroral fragmentation into patches

    Science.gov (United States)

    Hashimoto, Ayumi; Shiokawa, Kazuo; Otsuka, Yuichi; Oyama, Shin-ichiro; Nozawa, Satonori; Hori, Tomoaki; Lester, Mark; Johnsen, Magnar Gullikstad

    2015-08-01

    The study of auroral dynamics is important when considering disturbances of the magnetosphere. Shiokawa et al. (2010, 2014) reported observations of finger-like auroral structures that cause auroral fragmentation. Those structures are probably produced by macroscopic instabilities in the magnetosphere, mainly of the Rayleigh-Taylor type. However, the statistical characteristics of these structures have not yet been investigated. Here based on observations by an all-sky imager at Tromsø (magnetic latitude = 67.1°N), Norway, over three winter seasons, we statistically analyzed the occurrence conditions of 14 large-scale finger-like structures that developed from large-scale auroral regions including arcs and 6 small-scale finger-like structures that developed in auroral patches. The large-scale structures were seen from midnight to dawn local time and usually appeared at the beginning of the substorm recovery phase, near the low-latitude boundary of the auroral region. The small-scale structures were primarily seen at dawn and mainly occurred in the late recovery phase of substorms. The sizes of these large- and small-scale structures mapped in the magnetospheric equatorial plane are usually larger than the gyroradius of 10 keV protons, indicating that the finger-like structures could be caused by magnetohydrodynamic instabilities. However, the scale of small structures is only twice the gyroradius of 10 keV protons, suggesting that finite Larmor radius effects may contribute to the formation of small-scale structures. The eastward propagation velocities of the structures are -40 to +200 m/s and are comparable with those of plasma drift velocities measured by the colocating Super Dual Auroral Radar Network radar.

  1. Numerical modeling of the equatorial electrojet UT-variation on the basis of the model GSM TIP

    Directory of Open Access Journals (Sweden)

    M. V. Klimenko

    2007-06-01

    Full Text Available In the presented work the results of numerical modeling of the UT-variation of the equatorial electrojet, executed on the basis of the model GSM TIP are presented, taking into account the dynamo electric fields generated by thermospheric winds in a current-carrying layer of the ionosphere at heights 80–175 km above a surface of the Earth. To the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP, developed in WD IZMIRAN, a new block for the calculation of electric fields in the ionosphere has been added. In this block the solution of the three-dimensional equation describing the conservation law of the full current in the Earth's ionosphere is reduced to the solution of the two-dimensional equation by integration along geomagnetic field lines. Calculations of parameters of the near-Earth space plasmas have been executed for quiet equinoctial conditions on 22 March 1987 during the minimum of solar activity.

    It has been shown, that there is a distinct semidiurnal harmonic in the diurnal behavior of the linear density of the equatorial electrojet with maxima at 23:00 UT and 15:00 UT, as well as with minima at 06:00 UT and 20:00 UT. The greatest and smallest values of the peak intensity of the equatorial electrojet with respect to the diurnal behavior can differ by a factor of two. The longitudinal extent of the area of the equatorial electrojet does hardly show any UT-variation, but the greatest longitudinal extent is at 06 UT. With the growth of the peak intensity of the equatorial electrojet its latitudinal extent also increases (on ~5–10° a little. At the same time the equatorial electrojet in the maxima of intensity has approximately an identical width, whereas in the minima the electrojet is narrow in the morning and wide in the afternoon.

    As for the surface density of the equatorial electrojet, its UT-variation is much weaker and equals ~1–3 A/km2 and the peak

  2. The convection electric field in auroral substorms

    DEFF Research Database (Denmark)

    Gjerløv, Jesper Wittendorff; Hoffman, R.A.

    2001-01-01

    Dynamics Explorer 2 (DE 2) electric field and ion drift data are used in a statistical study of the ionospheric convection electric field in bulge-type auroral substorms. Thirty-one individual DE 2 substorm crossings were carefully selected and organized by the use of global auroral images obtained...... by DE 1. The selected passes, which occurred during substorm expansion phase, maximum, or early recovery phase, cover the entire nighttime substorm. The organization of the data used the method developed by Fujii et al. [1994], which divided the data into six local time sectors covering the nighttime...

  3. Auroral motions and magnetic variations associated with the onset of auroral substorms

    Energy Technology Data Exchange (ETDEWEB)

    Kawasaki, K.; Rostoker, G.

    1979-12-01

    Observations of the aurora borealis were undertaken during the period August 10--20, 1976, from Fort Smith, Northwest Territories, Canada. Two auroral substorm 'breakup' events which occurred in the Alberta sector during this period were photographically documented and have been studied together with the associated polar magnetic substorm events. It is found that significant westward-directed ionospheric current flow occurs for perhaps 2 or 3 minutes prior to the appearance of the auroral breakup surge form. This current appears to lie parallel to the bright arc which forms before onset of the breakup phase. Such an observation is important relative to the timing of the onsets both of auroral and polar magnetic substorms, and also may have critical implications relative to a theoretical understanding of the sequence of events leading to the auroral substorm breakup.

  4. Project CONDOR: Middle atmosphere wind structure obtained with lightweight inflatable spheres near the equatorial electrojet

    Science.gov (United States)

    Schmidlin, F. J.

    1987-01-01

    Observed correlations between the atmospheric electric field and the neutral wind were studied using additional atmospheric measurements during Project CONDOR. Project CONDOR obtained measurements near the equatorial electrojet (12 S) during March 1983. Neutral atmosphere wind measurements were obtained using lightweight inflatable spheres and temperatures were obtained using a datasonde. The lightweight sphere technology, the wind structure, and temperature structure are described. Results show that the lightweight sphere gives higher vertical resolution of winds below 75 km compared with the standard sphere, but gives little or no improvement above 80 km, and no usable temperature and density data.

  5. Morphology of Southern Hemisphere Riometer Auroral Absorption

    Science.gov (United States)

    2006-06-01

    range of frequencies used an inverse -square frequency dependence approximately holds. Morphology of Southern Hemisphere Riometer Auroral Absorption...Tecnológico under Proyecto No 1940934. Annex The percentage probability, QA, that an absorption A dB is exceed, is given as: Where Am is

  6. Numerical and laboratory simulations of auroral acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Gunell, H.; De Keyser, J. [1Belgian Institute for Space Aeronomy, Avenue Circulaire 3, B-1180 Brussels (Belgium); Mann, I. [EISCAT Scientific Association, P.O. Box 812, SE-981 28 Kiruna, Sweden and Department of Physics, Umeå University, SE-901 87 Umeå (Sweden)

    2013-10-15

    The existence of parallel electric fields is an essential ingredient of auroral physics, leading to the acceleration of particles that give rise to the auroral displays. An auroral flux tube is modelled using electrostatic Vlasov simulations, and the results are compared to simulations of a proposed laboratory device that is meant for studies of the plasma physical processes that occur on auroral field lines. The hot magnetospheric plasma is represented by a gas discharge plasma source in the laboratory device, and the cold plasma mimicking the ionospheric plasma is generated by a Q-machine source. In both systems, double layers form with plasma density gradients concentrated on their high potential sides. The systems differ regarding the properties of ion acoustic waves that are heavily damped in the magnetosphere, where the ion population is hot, but weakly damped in the laboratory, where the discharge ions are cold. Ion waves are excited by the ion beam that is created by acceleration in the double layer in both systems. The efficiency of this beam-plasma interaction depends on the acceleration voltage. For voltages where the interaction is less efficient, the laboratory experiment is more space-like.

  7. Equatorial electrojet in the Indian region during the geomagnetic storm of 13–14 November 1998

    Indian Academy of Sciences (India)

    H Chandra; R G Rastogi; R K Choudhary; Som Sharma

    2016-04-01

    The geomagnetic storm of November 1998 is a unique event where IMF-Bz remained southward withvalues exceeding –15 nT for more than a day. The SYM/H index decreased from about 07 hr on 13November 1998 reaching a minimum of about –120 nT around midnight of 13–14 November 1998.Features of the equatorial electrojet in the Indian region are studied during the geomagnetic storm eventof 13–14 November 1998, based on the geomagnetic data from the chain of observatories in India. Suddennorthward turning of IMF-Bz for a very short duration around 08 hr on 13 November 1998 resultedin a small and very short duration counter electrojet. A strong (–50 nT) and a long duration counterelectrojet, right from 08 to 13 hr on 14 November 1998 was observed resulting in the absence of equatorialEs at Thumba. Absence of the equatorial ionization anomaly was also observed as seen from theionograms over Thumba and ionspheric data from Ahmedabad. The delayed effect on 14 November 1998is due to the disturbance dynamo effect.

  8. Harmonic H sup + gyrofrequency structures in auroral hiss observed by high-altitude auroral sounding rockets

    Energy Technology Data Exchange (ETDEWEB)

    Kintner, P.M.; Vago, J. (Cornell Univ., Ithaca, NY (USA)); Scales, W. (Naval Research Lab., Washington, DC (USA)); Yau, A.; Whalen, B. (National Research Council of Canada, Ottwawa, Ontario (Canada)); Arnoldy, R. (Univ. of New Hampshire, Durham (USA)); Moore, T. (Marshall Space Flight Center, Huntsville, AL (USA))

    1991-06-01

    Two recent sounding rocket experiments have yielded VLF wave data with spectral structures ordered by the hydrogen gyrofrequency. The spectral structures occur near and above the lower hybrid frequency in association with auroral hiss. These structures are observed within and near regions of auroral electron precipitation and transverse ion acceleration. They are accompanied by auroral hiss but are anticorrelated with spectral peaks at the lower hybrid frequency. They are typically found above 500 km altitude, have no measureable magnetic component, and are at least occasionally short wavelength (k{rho}{sub i}{ge}1). Because the spectral structures appear to be electrostatic, are ordered by the hydrogen gyrofrequency, and are short wavelength, the authors interpret the structures as modes which connect the lower hybrid mode with the hydrogen Bernstein modes. A study of the plasma wave mode structure in the vicinity of the lower hybrid frequency is presented to substantiate this interpretation. The results imply that these waves are a common feature of the auroral zone ionosphere above 500 km altitude and exist any time that auroral hiss exists. The absence of previous satellite abservations of this phenomenon can be explained by Doppler broadening.

  9. Statistics of auroral hiss and relationship to auroral boundaries and upward current regions

    Science.gov (United States)

    Spasojevic, M.

    2016-08-01

    An 8 year database of VLF auroral hiss observations from South Pole station (invariant latitude of -74° with magnetic local time (MLT) = UT -3.5 h) is analyzed. There are three peaks in hiss occurrence as a function of MLT in the evening sector (19-23 MLT), afternoon sector (13-17 MLT), and morning sector (7-11 MLT). The geomagnetic and interplanetary magnetic field (IMF) drivers of hiss are examined in the three MLT sectors, and the results are interpreted using an empirical model of auroral boundaries and an empirical model of field-aligned current patterns. Auroral hiss on the dayside occurs when the auroral oval is centered near the latitude of the station, and in the afternoon sector higher disturbance levels are required. The afternoon sector favors positive By when Bz is positive and negative By when Bz is strongly negative, while the morning sector favors the complementary conditions. In each case the preference for hiss occurrence follows the pattern of upward field-aligned currents, and hiss is more likely in the configuration where the peak in the upward current is closer to the latitude of the station. IMF By does not play a role on the nightside where hiss is most likely to occur during moderately weak driving conditions as higher disturbance levels are expected to move the auroral oval and upward current systems to latitudes well equatorward of South Pole.

  10. Auroral meridian scanning photometer calibration using Jupiter

    Science.gov (United States)

    Jackel, Brian J.; Unick, Craig; Creutzberg, Fokke; Baker, Greg; Davis, Eric; Donovan, Eric F.; Connors, Martin; Wilson, Cody; Little, Jarrett; Greffen, M.; McGuffin, Neil

    2016-10-01

    Observations of astronomical sources provide information that can significantly enhance the utility of auroral data for scientific studies. This report presents results obtained by using Jupiter for field cross calibration of four multispectral auroral meridian scanning photometers during the 2011-2015 Northern Hemisphere winters. Seasonal average optical field-of-view and local orientation estimates are obtained with uncertainties of 0.01 and 0.1°, respectively. Estimates of absolute sensitivity are repeatable to roughly 5 % from one month to the next, while the relative response between different wavelength channels is stable to better than 1 %. Astronomical field calibrations and darkroom calibration differences are on the order of 10 %. Atmospheric variability is the primary source of uncertainty; this may be reduced with complementary data from co-located instruments.

  11. The Auroral Station in Adventdalen, Svalbard

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    This paper describes the Auroral Station in Adventdalen near Longyearbyen, Svalbard (78°N, 15°E). The main instruments at the site are for optical observation of aurora and airglow, but magnetic and radar observations are also carried out. Emission spectra show the difference between the dayside and nightside optical aurora. A newly compiled mesospheric temperature series from the station is also presented, derived through 20 years of spectral measurements of the hydroxyl airglow layer.

  12. Comparative Statistical Analysis of Auroral Models

    Science.gov (United States)

    2012-03-22

    heated and compressed but maintain a nearly Maxwellian energy distribution (Paschmann, 2003). Second, they encounter a region, as is shown in Figure 5...auroral oval. This occurs because the particle energies found within the main plasma sheet have a much more Maxwellian distribution that those that have...average. An example of this is shown in Figure 17. These occurrences were also deemed non -physical, and the boundary coordinate was excluded from

  13. Tail reconnection region versus auroral activity inferred from conjugate ARTEMIS plasma sheet flow and auroral observations

    Science.gov (United States)

    Nishimura, Y.; Lyons, L. R.; Xing, X.; Angelopoulos, V.; Donovan, E. F.; Mende, S. B.; Bonnell, J. W.; Auster, U.

    2013-09-01

    sheet flow bursts have been suggested to correspond to different types of auroral activity, such as poleward boundary intensifications (PBIs), ensuing auroral streamers, and substorms. The flow-aurora association leads to the important question of identifying the magnetotail source region for the flow bursts and how this region depends on magnetic activity. The present study uses the ARTEMIS spacecraft coordinated with conjugate ground-based auroral imager observations to identify flow bursts beyond 45 RE downtail and corresponding auroral forms. We find that quiet-time flows are directed dominantly earthward with a one-to-one correspondence with PBIs. Flow bursts during the substorm recovery phase and during steady magnetospheric convection (SMC) periods are also directed earthward, and these flows are associated with a series of PBIs/streamers lasting for tens of minutes with similar durations to that of the series of earthward flows. Presubstorm onset flows are also earthward and associated with PBIs/streamers. The earthward flows during those magnetic conditions suggest that the flow bursts, which lead to PBIs and streamers, originate from further downtail of ARTEMIS, possibly from the distant-tail neutral line (DNL) or tailward-retreated near-Earth neutral line (NENL) rather than from the nominal NENL location in the midtail. We find that tailward flows are limited primarily to the substorm expansion phase. They continue throughout the period of auroral poleward expansion, indicating that the expansion-phase flows originate from the NENL and that NENL activity is closely related to the auroral expansion of the substorm expansion phase.

  14. Multiscale Equatorial Electrojet Turbulence: Energy Conservation, Coupling, and Cascades in a Baseline 2-D Fluid Model

    CERN Document Server

    Hassan, Ehab; Morrison, P J; Horton, W

    2016-01-01

    Progress in understanding the coupling between plasma instabilities in the equatorial electrojet based on a unified fluid model is reported. A deeper understanding of the linear and nonlinear evolution and the coupling of the gradient-drift and Farley-Buneman instabilities is achieved by studying the e?ect of di?erent combinations of the density-gradient scale-lengths (Ln) and cross-?eld (E?B) drifts on the plasma turbulence. Mechanisms and channels of energy transfer are illucidated for these multiscale instabilities. Energy for the uni?ed model is examined, including the injected, conservative redistribution (between ?elds and scales), and ultimate dissipation. Various physical mechanisms involved in the energetics are categorized as sources, sinks, nonlinear transfer, and coupling to show that the system satisfies the fundamental law of energy Oonservation. The physics of the nonlinear transfer terms is studied to identify their roles in producing energy cascades { the transference of energy from the domin...

  15. Investigations of the auroral luminosity distribution and the dynamics of discrete auroral forms in a historical retrospective

    Science.gov (United States)

    Feldstein, Y. I.; Vorobjev, V. G.; Zverev, V. L.; Förster, M.

    2014-05-01

    Research results about planetary-scale auroral distributions are presented in a historical retrospective, beginning with the first "maps of isochasms" - lines of equal visibility of auroras in the firmament (Fig. 2) - up to "isoaurora maps" - lines of equal occurrence frequency of auroras in the zenith (Fig. 4). The exploration of auroras in Russia from Lomonosov in the 18th century (Fig. 1) until the start of the International Geophysical Year (IGY) in 1957 is shortly summed up. A generalised pattern of discrete auroral forms along the auroral oval during geomagnetically very quiet intervals is presented in Fig. 5. The changes of discrete auroral forms versus local time exhibit a fixed pattern with respect to the sun. The auroral forms comprise rays near noon, homogeneous arcs during the evening, and rayed arcs and bands during the night and in the morning. This fixed auroral pattern is unsettled during disturbances, which occur sometimes even during very quiet intervals. The azimuths of extended auroral forms vary with local time. Such variations in the orientation of extended forms above stations in the auroral zone have been used by various investigators to determine the position of the auroral oval (Fig. 9). Auroral luminosity of the daytime and nighttime sectors differ owing to different luminosity forms, directions of motion of the discrete forms, the height of the luminescent layers, and the spectral composition (predominant red emissions during daytime and green emissions during the night). Schemes that summarise principal peculiarities of daytime luminosity, its structure in MLT (magnetic local time) and MLat (magnetic latitude) coordinates, and the spectral composition of the luminosity are presented in Figs. 15 and 19. We discuss in detail the daytime sector dynamics of individual discrete forms for both quiet conditions and auroral substorms. The most important auroral changes during substorms occur in the nighttime sector. We present the evolution of

  16. Spacecraft Charging and Auroral Boundary Predictions in Low Earth Orbit

    Science.gov (United States)

    Minow, Joseph I.

    2016-01-01

    Auroral charging of spacecraft is an important class of space weather impacts on technological systems in low Earth orbit. In order for space weather models to accurately specify auroral charging environments, they must provide the appropriate plasma environment characteristics responsible for charging. Improvements in operational space weather prediction capabilities relevant to charging must be tested against charging observations.

  17. Effect of Energetic Electrons on Quiet Auroral Arc Formation

    Science.gov (United States)

    Hasegawa, Hiroki; Ohno, Nobuaki; Sato, Tetsuya

    2010-11-01

    The theory of feedback instability between the magnetosphere and ionosphere is believed as one of the candidate to explain the formation of quiet auroral arc. Then, some magneto-hydro- dynamics simulations showed the arc formation by this macroscopic instability, while the effect of auroral energetic electrons on the arc formation was neglected or given as a macroscopic parameter in these simulations. On the other hand, because of the recent development of particle simulations, auroral energetic electrons are thought to be produced by the super ion-acoustic double layer that should be created by microscopic instability. To make close investigation of auroral arc formation, it is necessary to consider the interaction with microscopic instability. In this paper, we numerically study the effect of energetic electrons on quiet auroral arc formation by means of the Macro-Micro Interlocked simulation.

  18. Magnetotail energy dissipation during an auroral substorm

    Science.gov (United States)

    Panov, E. V.; Baumjohann, W.; Wolf, R. A.; Nakamura, R.; Angelopoulos, V.; Weygand, J. M.; Kubyshkina, M. V.

    2016-12-01

    Violent releases of space plasma energy from the Earth's magnetotail during substorms produce strong electric currents and bright aurora. But what modulates these currents and aurora and controls dissipation of the energy released in the ionosphere? Using data from the THEMIS fleet of satellites and ground-based imagers and magnetometers, we show that plasma energy dissipation is controlled by field-aligned currents (FACs) produced and modulated during magnetotail topology change and oscillatory braking of fast plasma jets at 10-14 Earth radii in the nightside magnetosphere. FACs appear in regions where plasma sheet pressure and flux tube volume gradients are non-collinear. Faster tailward expansion of magnetotail dipolarization and subsequent slower inner plasma sheet restretching during substorm expansion and recovery phases cause faster poleward then slower equatorward movement of the substorm aurora. Anharmonic radial plasma oscillations build up displaced current filaments and are responsible for discrete longitudinal auroral arcs that move equatorward at a velocity of about 1 km s-1. This observed auroral activity appears sufficient to dissipate the released energy.

  19. Carl Størmer Auroral Pioneer

    CERN Document Server

    Egeland, Alv

    2013-01-01

    This biography summarizes the seminal contributions to auroral and space science of Carl Størmer (1874 - 1957). He was the first to develop precise photographic methods to calculate heights and morphologies of diverse auroral forms during four solar cycles. Størmer independently devised numerical techniques to determine the trajectories of high-energy charged particles allowed and forbidden in the Earth’s magnetic field. His theoretical analyses explained cosmic ray access to the upper atmosphere, 20 years before they were identified by other scientists. Størmer’s crowning achievement, “The Polar Aurora,” published when he was 81 years old, stands to this day as a regularly cited guide in graduate-level courses on space physics.   The authors present the life of this prodigious scientist in relation to the cultural life of early 20th century in Norway and to the development of the space sciences in the post-Sputnik era.

  20. Mapping thermospheric winds in the auroral zone

    Science.gov (United States)

    Conde, M.; Smith, R. W.

    A new all-sky imaging Fabry-Perot (ASIFP) spectrometer has been developed for ground-based mapping of upper atmospheric wind and temperature fields in the auroral zone. Although several other ASIFP spectrometers exist for atmospheric studies [Rees et al., 1984; Sekar et al., 1993; Biondi et al., 1995] these instruments have all operated with etalons of fixed optical gap, a method potentially subject to errors in the presence of auroral intensity gradients. In this instrument the etalon plate spacing is scanned periodically over one order of interference and each photon detected is assigned to a wavelength interval which is determined from both its arrival location on the detector and the etalon plate spacing prevailing at the detection time. Spectra accumulated this way are not distorted by spatial intensity gradients. Preliminary λ630 nm observations were made during the winter of 1994/95 from Poker Flat Research Range, Alaska. To illustrate some of the features we have observed in this study we present line-of-sight wind estimates derived for the night of December 7, 1994. The background wind matches averages presented previously by Sica et al. [1986] and is consistent with winds driven principally by momentum deposition from ionospheric plasma convection through ion-drag. Smaller scale curvature and divergence features are also discernable and are discussed.

  1. The auroral footprint of Enceladus on Saturn.

    Science.gov (United States)

    Pryor, Wayne R; Rymer, Abigail M; Mitchell, Donald G; Hill, Thomas W; Young, David T; Saur, Joachim; Jones, Geraint H; Jacobsen, Sven; Cowley, Stan W H; Mauk, Barry H; Coates, Andrew J; Gustin, Jacques; Grodent, Denis; Gérard, Jean-Claude; Lamy, Laurent; Nichols, Jonathan D; Krimigis, Stamatios M; Esposito, Larry W; Dougherty, Michele K; Jouchoux, Alain J; Stewart, A Ian F; McClintock, William E; Holsclaw, Gregory M; Ajello, Joseph M; Colwell, Joshua E; Hendrix, Amanda R; Crary, Frank J; Clarke, John T; Zhou, Xiaoyan

    2011-04-21

    Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity.

  2. Sophus Peter Tromholt: an outstanding pioneer in auroral research

    Directory of Open Access Journals (Sweden)

    K. Moss

    2012-03-01

    Full Text Available The Danish school teacher Sophus Peter Tromholt (1851–1896 was self-taught in physics, astronomy, and auroral sciences. Still, he was one of the brightest auroral researchers of the 19th century. He was the first scientist ever to organize and analyse correlated auroral observations over a wide area (entire Scandinavia moving away from incomplete localized observations. Tromholt documented the relation between auroras and sunspots and demonstrated the daily, seasonal and solar cycle-related variations in high-latitude auroral occurrence frequencies. Thus, Tromholt was the first ever to deduce from auroral observations the variations associated with what is now known as the auroral oval termed so by Khorosheva (1962 and Feldstein (1963 more than 80 yr later. He made reliable and accurate estimates of the heights of auroras several decades before this important issue was finally settled through Størmer's brilliant photographic technique. In addition to his three major scientific works (Tromholt, 1880a, 1882a, and 1885a, he wrote numerous short science notes and made huge efforts to collect historical auroral observations (Tromholt, 1898. Furthermore, Tromholt wrote a large number of popular science articles in newspapers and journals and made lecture tours all over Scandinavia and Germany, contributing to enhance the public educational level and awareness. He devoted most of his life to auroral research but as a self-taught scientist, he received little acclaim within the contemporary academic scientific society. With his non-academic background, trained at a college of education – not a university – he was never offered a position at a university or a research institution. However, Sophus Tromholt was an outstanding pioneer in auroral research.

  3. Generation of auroral kilometric radiation in inhomogeneous magnetospheric plasma

    Science.gov (United States)

    Burinskaya, T. M.; Shevelev, M. M.

    2017-01-01

    The generation of auroral kilometric radiation in a narrow 3D plasma cavity, in which a weakly relativistic electron flow is propagated along the magnetic field against a low-density cold background plasma, is studied. The time dynamics of the propagation and intensification of waves are analyzed using geometric optics equations. The waves have different wave vector components and start from the cavity center at an altitude of about the Earth's radius at plasma parameters typical for the auroral zone at this altitude. It is shown that the global inhomogeneity of the Earth's magnetic field is of key importance in shaping the auroral kilometric radiation spectra.

  4. Mesoscale ionospheric tomography at the Auroral region

    Science.gov (United States)

    Luntama, J.; Kokkatil, G. V.

    2008-12-01

    FMI (Finnish Meteorological Institute) has used observations from the dense GNSS network in Finland for high resolution regional ionospheric tomography. The observation system used in this work is the VRS (Virtual Reference Station) network in Finland operated by Geotrim Ltd. This network contains 86 GNSS ground stations providing two frequency GPS and GLONASS observations with the sampling rate of 1 Hz. The network covers the whole Finland and the sampling of the ionosphere is very good for observing mesoscale ionospheric structures at the Auroral region. The ionospheric tomography software used by FMI is the MIDAS (Multi-Instrument Data Analysis System) algorithm developed and implemented by the University of Bath (Mitchell and Spencer, 2003). MIDAS is a 3-D extension of the 2-D tomography algorithm originally presented by Fremouw et al. (1992). The research at FMI is based on ground based GNSS data collected in December 2006. The impacts of the two geomagnetic storms during the month are clearly visible in the retrieved electron density and TEC maps and they can be correlated with the magnetic field disturbances measured by the IMAGE magnetometer network. This is the first time that mesoscale structures in the ionospheric plasma can be detected from ground based GNSS observations at the Auroral region. The continuous high rate observation data from the Geotrim network allows monitoring of the temporal evolution of these structures throughout the storms. Validation of the high resolution electron density and TEC maps is a challenge as independent reference observations with a similar resolution are not available. FMI has compared the 3-D electron density maps against the 2-D electron density plots retrieved from the observations from the Ionospheric Tomography Chain operated by the Sodankylä Geophysical Observatory (SGO). Additional validation has been performed with intercomparisons with observations from the ground based magnetometer and auroral camera network

  5. Imaging radar observations and nonlocal theory of large-scale plasma waves in the equatorial electrojet

    Directory of Open Access Journals (Sweden)

    D. L. Hysell

    Full Text Available Large-scale (l ~ 1 km waves in the daytime and night-time equatorial electrojet are studied using coherent scatter radar data from Jicamarca. Images of plasma irregularities within the main beam of the radar are formed using interferometry with multiple baselines. These images are analyzed according to nonlocal gradient drift instability theory and are also compared to nonlinear computer simulations carried out recently by Ronchi et al. (1991 and Hu and Bhattacharjee (1999. In the daytime, the large-scale waves assume a non-steady dynamical equilibrium state characterized by the straining and destruction of the waves by shear and diffusion followed by spontaneous regeneration as predicted by Ronchi et al. (1991. At night, when steep plasma density gradients emerge, slowly propagating large-scale vertically extended waves predominate. Eikonal analysis suggests that these waves are trapped (absolutely unstable or are nearly trapped (convectively unstable and are able to tunnel between altitude regions which are locally unstable. Intermediate-scale waves are mainly transient (convectively stable but can become absolutely unstable in narrow altitude bands determined by the background density profile. These characteristics are mainly consistent with the simulations presented by Hu and Bhattacharjee (1999. A new class of large-scale primary waves is found to occur along bands that sweep westward and downward from high altitudes through the E-region at twilight.

    Key words. Ionosphere (equatorial ionosphere; ionospheric irregularities; plasma waves and instabilities

  6. Are the equatorial electrojet and the Sq coupled systems? Transfer entropy approach

    Science.gov (United States)

    Vichare, Geeta; Bhaskar, Ankush; Ramesh, Durbha Sai

    2016-05-01

    Whether equatorial electrojet (EEJ) and solar quiet (Sq) are independent systems or not is a long standing question. Techniques such as correlation analysis, interpretation of the westward currents observed between EEJ and Sq focus, along with the simulation studies have been used to address this question, hitherto. In this article, we revisit this problem using a method based on transfer entropy that examines the relationship between day-to-day variability in EEJ and Sq during low solar activity period (year 2007-08). Magnetic field variations in the horizontal component from the geomagnetic observatory, Tirunelveli (TIR) from the Indian region are used as a proxy for EEJ currents. To represent variations of Sq current system, two stations outside the EEJ belt, Nagpur (NGP) and Jaipur (JAI) are analyzed. Our analyses clearly demonstrate that significant information is exchanged between EEJ and Sq variations, and hence they are in a cross-talk with each other, indicating EEJ and Sq are coupled systems. Variations of time scales less than 2 h appear at the equatorial station before Sq stations. Similar analyses carried out for the African sector also validate the above results.

  7. Automatic Georeferencing of Astronaut Auroral Photography

    Science.gov (United States)

    Walsh, A. P.; Riechert, M.; Taylor, M. G.

    2014-12-01

    Astronauts on board the International Space Station have taken thousands of high quality photographs of the aurorae borealis and australis with a high temporal and spatial resolution. A barrier to these photographs being used in research is that the cameras do not have a fixed orientation and the images therefore do not have any pointing information associated with them. Using astrometry.net and other open source libraries we have developed a software toolkit to automatically reconstruct the pointing of the images from the visible starfield and hence project the auroral images in geographic and geomagnetic coordinates. Here we explain the technique and the resulting data products, which will soon be publically available through the project website.

  8. Generation of auroral turbulence through the magnetosphere-ionosphere coupling

    Science.gov (United States)

    Watanabe, Tomo-Hiko; Kurata, Hiroaki; Maeyama, Shinya

    2016-12-01

    The shear Alfvén waves coupled with the ionospheric density fluctuations in auroral regions of a planetary magnetosphere are modeled by a set of the reduced magnetohydrodynamic and two-fluid equations. When the drift velocity of the magnetized plasma due to the background electric field exceeds a critical value, the magnetosphere-ionosphere (M-I) coupling system is unstable to the feedback instability which leads to formation of auroral arc structures with ionospheric density and current enhancements. As the feedback (primary) instability grows, a secondary mode appears and deforms the auroral structures. A perturbative (quasilinear) analysis clarifies the secondary growth of the Kelvin-Helmholtz type instability driven by the primary instability growth in the feedback M-I coupling. In the nonlinear stage of the feedback instability, furthermore, auroral turbulence is spontaneously generated, where the equipartition of kinetic and magnetic energy is confirmed in the quasi-steady turbulence.

  9. First results of the Auroral Turbulance II rocket experiment

    DEFF Research Database (Denmark)

    Danielides, M.A.; Ranta, A.; Ivchenco, N.;

    1999-01-01

    was to study the fine structure of an active auroral arc. Ground based observations were done by a chain all-sky cameras, a photometer and a magnetometer at Poker Flat. The satellite coverage was obtained by POLAR UV imager and GOES 8 and 9 magnetometer. The three point measurement allows the distinction...... of spatial and temporal variations. The first results of the magnetic, [1,2], electric and particle data analysis are compared with optical observations [2] of auroral structures....

  10. RFP for the Auroral Multiscale Midex (AMM) Mission star tracker

    DEFF Research Database (Denmark)

    Riis, Troels; Betto, Maurizio; Jørgensen, John Leif;

    1999-01-01

    This document is in response to the John Hopkins University - Applied Physics Laboratory RFP for the Auroral Multiscale Midex Mission star tracker.It describes the functionality, the requirements and the performance of the ASC Star Tracker.......This document is in response to the John Hopkins University - Applied Physics Laboratory RFP for the Auroral Multiscale Midex Mission star tracker.It describes the functionality, the requirements and the performance of the ASC Star Tracker....

  11. DISCOVERY OF A DARK AURORAL OVAL ON SATURN

    Science.gov (United States)

    2002-01-01

    The ultraviolet image was obtained by the NASA/ESA Hubble Space Telescope with the European Faint Object Camera (FOC) on June 1992. It represents the sunlight reflected by the planet in the near UV (220 nm). * The image reveals a dark oval encircling the north magnetic pole of Saturn. This auroral oval is the first ever observed for Saturn, and its darkness is unique in the solar system (L. Ben-Jaffel, V. Leers, B. Sandel, Science, Vol. 269, p. 951, August 18, 1995). The structure represents an excess of absorption of the sunlight at 220 nm by atmospheric particles that are the product of the auroral activity itself. The large tilt of the northern pole of Saturn at the time of observation, and the almost perfect symmetry of the planet's magnetic field, made this observation unique as even the far side of the dark oval across the pole is visible! * Auroral activity is usually characterized by light emitted around the poles. The dark oval observed for Saturn is a STUNNING VISUAL PROOF that transport of energy and charged particles from the magnetosphere to the atmosphere of the planet at high latitudes induces an auroral activity that not only produces auroral LIGHT but also UV-DARK material near the poles: auroral electrons are probably initiating hydrocarbon polymer formation in these regions. Credits: L. Ben Jaffel, Institut d'Astrophysique de Paris-CNRS, France, B. Sandel (Univ. of Arizona), NASA/ESA, and Science (magazine).

  12. ESA's Cluster solved an auroral puzzle

    Science.gov (United States)

    2003-05-01

    These aurorae - seen as bright spots in Earth’s atmosphere and called ‘dayside proton auroral spots’ - occur when fractures appear in the Earth’s magnetic field, allowing particles given out from the Sun to squirt through and collide with the molecules in our atmosphere. This is the first time that a precise and direct connection between the two events has been made. The Earth’s magnetic field acts like a shield, protecting Earth from the constant stream of tiny particles ejected by the Sun and known as the ‘solar wind’. The solar wind itself is made of hydrogen atoms, broken into their constituent pieces: protons and electrons. When electrons find routes into our atmosphere, they collide with and excite the atoms in the air. When these excited atoms release their energy, it is given out as light, creating the glowing ‘curtains’ we see as the aurora borealis (or the aurora australis in the southern hemisphere). Dayside proton auroral spots are caused by protons ‘stealing’ electrons from the atoms in our atmosphere. On 18 March last year, a jet of energetic solar protons collided with the Earth’s atmosphere and created a bright ‘spot’ seen by NASA’s IMAGE spacecraft, just as Cluster passed overhead and straight through the region where the proton jet was emanating. An extensive analysis of the Cluster results has now shown that the region was experiencing a turbulent event known as ‘magnetic reconnection’. Such a phenomenon takes place when the Earth’s usually impenetrable magnetic field fractures and has to find a new stable configuration. Until the field mends itself, solar protons leak through the gap and jet into Earth’s atmosphere creating the dayside proton aurora. Philippe Escoubet, ESA’s Cluster Project Scientist, comments, “Thanks to Cluster’s observations scientists can directly and firmly link for the first time a dayside proton auroral spot and a magnetic reconnection event.” Tai Phan, leading the

  13. Global characteristics of the lunar tidal modulation of the equatorial electrojet derived from CHAMP observations

    Science.gov (United States)

    Lühr, H.; Siddiqui, T. A.; Maus, S.

    2012-03-01

    It has been known since many decades that lunar tide has an influence on the strength of the equatorial electrojet (EEJ). There has, however, never been a comprehensive study of the tidal effect on a global scale. Based on the continuous magnetic field measurements by the CHAMP satellite over 10 years it is possible to investigate the various aspects of lunar effects on the EEJ. The EEJ intensity is enhanced around times when the moon is overhead or at the antipode. This effect is particularly strong around noon, shortly after new and full moon. The lunar tide manifests itself as a semi-diurnal wave that precesses through all local times within one lunar month. The largest tidal amplitudes are observed around December solstice and smallest around June solstice. The tidal wave crest lags behind the moon phase. During December this amounts to about 4 days while it is around 2 days during other times of the year. We have not found significant longitudinal variations of the lunar influence on the EEJ. When comparing the average EEJ amplitude at high solar activity with that during periods of solar minimum conditions a solar cycle dependence can be found, but the ratio between tidal amplitude and EEJ intensity stays the same. Actually, tidal signatures standout clearer during times of low solar activity. We suggest that the tidal variations are caused by a current system added to the EEJ rather than by modulating the EEJ. Gravitational forcing of the lower atmosphere by the moon and the sun is assumed to be the driver of an upward propagating tidal wave. The larger tidal amplitudes around December solstice can be related to stratospheric warming events which seem to improve the conditions for upward propagation. The results described here have to large extent been presented as a Julius-Bartels Medal Lecture during the General Assembly 2011 of the European Geosciences Union.

  14. Numerical Modeling of Equatorial Electrojet Behavior During April, 8, 2005 Solar Eclipse

    Science.gov (United States)

    Klimenko, M. V.; Klimenko, V. V.; Bryukhanov, V. V.

    2007-05-01

    In the given work the results of numerical calculations of global distribution of potential of electric field and linear density of zonal current in the ionosphere of the Earth during a solar eclipse are presented. Calculations have been executed on the basis of Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP), developed in WD IZMIRAN, added by the new block of calculation of electric fields in the ionosphere of the Earth. In calculations we considered superposition of magnetospheric convection electric field and dynamo field generated by thermospheric winds without taking into account the tides. The solar eclipse of hybrid type viewed in the given work has occurred on April, 8, 2005. The hybrid eclipse was visible from within a thin corridor, which traverses the Southern Hemisphere. The path of the shadow of the Moon has begun southeast of New Zealand and stretched across the Pacific Ocean to Panama, Columbia, and Venezuela. The eclipse has begun at 18.54 UT and has ended at 22.15 UT. From 20.30 UT till 21.10 UT the shadow of an eclipse transited in a neighborhood of geomagnetic equator. It is shown, that the solar eclipse caused impairment of equatorial electrojet intensity twice. First time it has occurred at the initial stage of the eclipse due to change in ionosphere conductivity in the region of influence of field aligned currents. It has led to change of distribution of magnetospheric convection electric field (18.58 UT - 19.06 UT). Second time it has occurred during the passage of a solar eclipse through geomagnetic equator with delay of 30 min (21.00 UT - 21.20 UT) due to local changes of ionospheric conductivity in the region of the eclipse and reorganization of thermospheric circulation to which the time delay is related. It has led to change of distribution of dynamo field in the region of geomagnetic equator.

  15. Global characteristics of the lunar tidal modulation of the equatorial electrojet derived from CHAMP observations

    Directory of Open Access Journals (Sweden)

    H. Lühr

    2012-03-01

    Full Text Available It has been known since many decades that lunar tide has an influence on the strength of the equatorial electrojet (EEJ. There has, however, never been a comprehensive study of the tidal effect on a global scale. Based on the continuous magnetic field measurements by the CHAMP satellite over 10 years it is possible to investigate the various aspects of lunar effects on the EEJ. The EEJ intensity is enhanced around times when the moon is overhead or at the antipode. This effect is particularly strong around noon, shortly after new and full moon. The lunar tide manifests itself as a semi-diurnal wave that precesses through all local times within one lunar month. The largest tidal amplitudes are observed around December solstice and smallest around June solstice. The tidal wave crest lags behind the moon phase. During December this amounts to about 4 days while it is around 2 days during other times of the year. We have not found significant longitudinal variations of the lunar influence on the EEJ. When comparing the average EEJ amplitude at high solar activity with that during periods of solar minimum conditions a solar cycle dependence can be found, but the ratio between tidal amplitude and EEJ intensity stays the same. Actually, tidal signatures standout clearer during times of low solar activity. We suggest that the tidal variations are caused by a current system added to the EEJ rather than by modulating the EEJ. Gravitational forcing of the lower atmosphere by the moon and the sun is assumed to be the driver of an upward propagating tidal wave. The larger tidal amplitudes around December solstice can be related to stratospheric warming events which seem to improve the conditions for upward propagation.

    The results described here have to large extent been presented as a Julius-Bartels Medal Lecture during the General Assembly 2011 of the European Geosciences Union.

  16. Influence of auroral streamers on rapid evolution of SAPS flows

    Science.gov (United States)

    Gallardo-Lacourt, B.; Nishimura, T.; Lyons, L. R.; Ruohoniemi, J. M.; Donovan, E.; Angelopoulos, V.; Nishitani, N.

    2015-12-01

    An important manifestation of plasma transport in the ionosphere is Subauroral Polarization Streams or SAPS, which are strong westward flow lying just equatorward of the electron auroral oval and thus of enhanced ionospheric conductivities of the auroral oval. While SAPS are known to intensify due to substorm injections, recent studies showed that large variability of SAPS flow can occur well after substorm onset and even during non-substorm times. These SAPS enhancements have been suggested to occur in association with auroral streamers that propagate equatorward, a suggestion that would indicate that plasma sheet fast flows propagate into the inner magnetosphere and increase subauroral flows. We present auroral images from the THEMIS ground-based all-sky-imager array and 2-d line-of-sight flow observations from the SuperDARN radars that share fields of view with the imagers to investigate systematically the association between SAPS and auroral streamers. We surveyed events from December 2007 to April 2013 for which high or mid-latitude SuperDARN radars were available to measure the SAPS flows, and identified 60 events. For streamers observed near the equatorward boundary of the auroral oval, we find westward flow enhancements of ~200 m/s slightly equatorward of the streamers. A preliminary survey suggests that >90% of the streamers that reach close to the equatorward boundary lead to westward flow enhancements. We also characterize the SAPS flow channel width and timing relative to streamers reaching radar echo meridians. The strong influence of auroral streamers on rapid SAPS flow evolution suggests that transient fast earthward plasma sheet flows can lead to westward SAPS flow enhancements in the subauroral region, and that such enhancements are far more common than only during substorms because of the frequent occurrences of streamers under various geomagnetic conditions.

  17. A linear auroral current-voltage relation in fluid theory

    Directory of Open Access Journals (Sweden)

    J. Vedin

    2004-04-01

    Full Text Available Progress in our understanding of auroral currents and auroral electron acceleration has for decades been hampered by an apparent incompatibility between kinetic and fluid models of the physics involved. A well established kinetic model predicts that steady upward field-aligned currents should be linearly related to the potential drop along the field line, but collisionless fluid models that reproduce this linear current-voltage relation have not been found. Using temperatures calculated from the kinetic model in the presence of an upward auroral current, we construct here approximants for the parallel and perpendicular temperatures. Although our model is rather simplified, we find that the fluid equations predict a realistic large-scale parallel electric field and a linear current-voltage relation when these approximants are employed as nonlocal equations of state. This suggests that the concepts we introduce can be applied to the development of accurate equations of state for fluid simulations of auroral flux tubes.

    Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions – Space plasma physics (kinetic and MHD theory

  18. Space Weather Monitoring for ISS Space Environments Engineering and Crew Auroral Observations

    Science.gov (United States)

    Minow, Joseph; Pettit, Donald R.; Hartman, William A.

    2012-01-01

    Today s presentation describes how real time space weather data is used by the International Space Station (ISS) space environments team to obtain data on auroral charging of the ISS vehicle and support ISS crew efforts to obtain auroral images from orbit. Topics covered include: Floating Potential Measurement Unit (FPMU), . Auroral charging of ISS, . Real ]time space weather monitoring resources, . Examples of ISS auroral charging captured from space weather events, . ISS crew observations of aurora.

  19. Auroral Kilometric Radiation and Type III Solar Radio Bursts

    Science.gov (United States)

    Romantsova, T. V.; Mogilevsky, M. M.; Skalsky, A. A.; Hanasz, J.

    2009-04-01

    Simultaneous wave observations onboard the ISEE-1 and ISEE-3 spacecraft show that onsets of the Auroral Kilometric Radiation frequently coincide with an arrival of type III solar burst (Calvert, 1981). It was supposed that solar burst stimulates maser instability in auroral region and AKR consequently . We present statistical and case studies of events when both type III solar radio bursts and Auroral Kilometric Radiation are recorded simultaneously. AKR was observed onboard the INTERBALL-2 spacecraft orbiting around the Earth by the POLRAD experiment. Wave measurements carried out onboard the Wind, INTEBALL-TAIL and Geotail spacecraft are used to identify unambiguously the type III solar radio bursts. The origin of close relation between onsets of both solar radiation and AKR is discussed and interpreted. Acknowledgements. This work is supported by grant RFBR 06-02-72560.

  20. The Auroral Planetary Imaging and Spectroscopy (APIS) service

    CERN Document Server

    Lamy, Laurent; Henry, Florence; Sidaner, Pierre Le

    2015-01-01

    The Auroral Planetary Imaging and Spectroscopy (APIS) service, accessible online, provides an open and interactive access to processed auroral observations of the outer planets and their satellites. Such observations are of interest for a wide community at the interface between planetology and magnetospheric and heliospheric physics. APIS consists of (i) a high level database, built from planetary auroral observations acquired by the Hubble Space Telescope (HST) since 1997 with its mostly used Far-UltraViolet spectro-imagers, (ii) a dedicated search interface aimed at browsing efficiently this database through relevant conditional search criteria and (iii) the ability to interactively work with the data online through plotting tools developed by the Virtual Observatory (VO) community, such as Aladin and Specview. This service is VO compliant and can therefore also been queried by external search tools of the VO community. The diversity of available data and the capability to sort them out by relevant physical...

  1. Intermittency of riometer auroral absorption observed at South Pole

    Science.gov (United States)

    Stepanova, M. V.; Antonova, E. E.; Foppiano, A. J.; Rosenberg, T. J.; Ovalle, E. M.

    2005-12-01

    Auroral radio-wave absorption values measured at South Pole for 3 years using a riometer are analyzed in order to test whether they show evidence of intermittency. The properties of the parameters of the probability density functions determined for several magnetic local time sectors are found to be significantly different. The probability density functions for the pre-midnight sector show the typical shape associated to intermittency. No results are given for the afternoon sector because few auroral absorption events meet the selection criteria to give statistically significant results. It is suggested that if the precipitating particle population responsible for the riometer auroral absorption shared the intermittency features of the absorption then the present results would allow the study of the properties of the induction component of magnetospheric turbulence.

  2. Fine Scale Structure observed in the Total Electron Content above the Sub-Auroral, Auroral, and Polar Ionosphere

    Science.gov (United States)

    Coster, A. J.; Thomas, E. G.; Vierinen, J.; Rideout, W. E.

    2015-12-01

    This paper details recent improvements in TEC observations made in the sub-auroral, auroral, and polar regions. The goal is high-resolution measurements of both medium and fine-scale TEC-gradients. To achieve this, the number of GNSS receivers processed was more than doubled, due to agreements made with multiple government and commercial agencies, such as those involved with highway transportation and precision farming. Following the increase in GNSS observations, additional improvements were made in the MIT Haystack GNSS data processing algorithms, allowing for finer grid spacing of the output TEC data. Merging data sets also increased sensitivity. Scintillation data from several GNSS receivers have been overlaid on top of all-sky camera images showing evidence of aurora. These data sets have been merged with the measured background TEC to monitor the development both medium and fine-scale TEC gradients. Data from multiple geomagnetic storms and auroral events in this solar cycle will be presented.

  3. Eyewitness Reports of the Great Auroral Storm of 1859

    Science.gov (United States)

    Green, James L.; Boardsen, Scott; Odenwald, Sten; Humble, John; Pazamickas, Katherine A.

    2005-01-01

    The great geomagnetic storm of 1859 is really composed of two closely spaced massive worldwide auroral events. The first event began on August 28th and the second began on September 2nd. It is the storm on September 2nd that results from the Carrington-Hodgson white light flare that occurred on the sun September l&. In addition to published scientific measurements; newspapers, ship logs and other records of that era provide an untapped wealth of first hand observations giving time and location along with reports of the auroral forms and colors. At its height, the aurora was described as a blood or deep crimson red that was so bright that one "could read a newspaper by." Several important aspects of this great geomagnetic storm are simply phenomenal. Auroral forms of all types and colors were observed to latitudes of 25deg and lower. A significant portion of the world's 125,000 miles of telegraph lines were also adversely affected. Many of - which were unusable for 8 hours or more and had a small but notable economic impact. T h s paper presents only a select few available first hand accounts of the Great Auroral Event of 1859 in an attempt to give the modern reader a sense of how this spectacular display was received by the public from many places around the globe and present some other important historical aspects of the storm.

  4. Relation of the auroral substorm to the substorm current wedge

    Science.gov (United States)

    McPherron, Robert L.; Chu, Xiangning

    2016-12-01

    The auroral substorm is an organized sequence of events seen in the aurora near midnight. It is a manifestation of the magnetospheric substorm which is a disturbance of the magnetosphere brought about by the solar wind transfer of magnetic flux from the dayside to the tail lobes and its return through the plasma sheet to the dayside. The most dramatic feature of the auroral substorm is the sudden brightening and poleward expansion of the aurora. Intimately associated with this expansion is a westward electrical current flowing across the bulge of expanding aurora. This current is fed by a downward field-aligned current (FAC) at its eastern edge and an upward current at its western edge. This current system is called the substorm current wedge (SCW). The SCW forms within a minute of auroral expansion. FAC are created by pressure gradients and field line bending from shears in plasma flow. Both of these are the result of pileup and diversion of plasma flows in the near-earth plasma sheet. The origins of these flows are reconnection sites further back in the tail. The auroral expansion can be explained by a combination of a change in field line mapping caused by the substorm current wedge and a tailward growth of the outer edge of the pileup region. We illustrate this scenario with a complex substorm and discuss some of the problems associated with this interpretation.

  5. Evolution of Jupiter's auroral-related stratospheric heating and chemistry

    Science.gov (United States)

    Sinclair, James; Orton, Glenn S.; Greathouse, Thomas K.; Fletcher, Leigh N.; Moses, Julianne I.; Hue, Vincent; Irwin, Patrick Gerard Joseph; Melin, Henrik; Giles, Rohini Sara

    2016-10-01

    Auroral processes on Jupiter are evident over a large range of wavelengths. Emission at X-ray, UV and near-infrared wavelengths highlights the precipitation of charged particles in Jupiter's ionosphere. Jupiter's auroral regions also exhibit enhanced mid-infrared emission of CH4 (7.8-μm), C2H2 (13-μm), C2H4 (10.5-μm) and C2H6 (12.2-μm), which indicates auroral processes modify the thermal structure and chemistry of the neutral stratosphere at pressures from 10 mbar to 10 μbar. In Sinclair et al., 2016a (submitted), 2016b (in preparation), we investigated these processes further by performing a retrieval analysis of Voyager-IRIS (Infrared Interferometer Spectrometer) observations measured in November 1979, Cassini-CIRS (Composite Infrared Spectrometer) observations measured in January 2001 and IRTF-TEXES (Texas Echelon Cross Echelle Spectrograph on NASA's Infrared Telescope Facility) spectra measured in December 2014. These datasets however captured Jupiter at significantly different epochs and thus the overall global evolution of atmospheric conditions as well as differences in spatial sampling, spectral resolution (and therefore vertical resolution in the atmosphere) have made inferences of the temporal evolution in auroral regions a challenge. However, in April 2016, we acquired IRTF-TEXES observations of Jupiter's high latitudes, using observing parameters very similar to those in December 2014. By performing a similar analysis of these observations and comparing results between December 2014 and April 2016, we can investigate the evolution of the thermal structure and chemistry in Jupiter's auroral regions over a 15 month timescale. The magnitude of temperature/composition changes and the altitudes at which they occur will provide insights into how auroral processes in the ionosphere propagate to the stratosphere. In particular, we can assess whether the evolution of stratospheric conditions in auroral regions is related to the decrease in solar activity

  6. Observations of transverse ion acceleration in the topside auroral ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Garbe, G.P.; Arnoldy, R.L. (Univ. of New Hampshire, Durham (United States)); Moore, T.E. (NASA Marshall Space Flight Center, Huntsville, AL (United States)); Kintner, P.M.; Vago, J.L. (Cornell Univ., Ithaca, NY (United States))

    1992-02-01

    Data obtained from a sounding rocket flight which reached an apogee of 927 km and passed through several auroral arcs are reported. During portions of the flight when the rocket was not in an energetic auroral structure, the ion data are fit to a Maxwellian function which yields the plasma parameters. Throughout the middle portion of the flight when above 700 km altitude, ion distributions having a superthermal tail were measured. These ion distributions generally coexisted with a cold thermal core distribution and peaked at pitch angles slightly greater than 90{degree}, which identifies them as conic distributions. These ions can be modeled using a bi-Maxwellian distribution function with a perpendicular (to B) temperature about 10 times greater than the parallel temperature of 0.15 eV. When the rocket was immersed in energetic auroral electron precipitation, two other ion distributions were observed. Transversely accelerated ions which represented bulk heating of the ambient population were observed. Transversely accelerated ions which represented bulk heating of the ambient population were observed continuously in these arcs. The characteristic perpendicular energy of the transversely bulk heated ions reached as high as 3 eV compared to typically less than 0.4 eV during nonauroral times. Cold ions flowing down the magnetic field were also continuously observed when the rocket was immersed in auroral electron precipitation and had downward speeds between 3 and 5 km/s. If one balances electric and collisional forces, these speeds translate to an electric field pointing into the atmosphere of magnitude 0.01 mV/m. A close correlation between auroral electron precipitation, measured electrostatic oxygen cyclotron waves, cold downflowing ions and transversely bulk heated ions will be shown.

  7. Threshold of auroral intensification reduced by electron precipitation effect

    CERN Document Server

    Hiraki, Yasutaka

    2016-01-01

    It has been known that discrete aurora suddenly intensifies and deforms from an arc-like to a variety of wavy/vortex structures, especially during a substorm period. The instability of Alfv$\\acute{\\rm e}$n waves reflected from the ionosphere has been analyzed in order to comprehend the ignition process of auroral intensification. It was presented that the prime key is an enhancement of plasma convection, and the convection electric field has a threshold. This study examined effects of auroral electron precipitation, causing the ionization of neutral atmosphere, on the linear instability of Alfv$\\acute{\\rm e}$n waves. It was found that the threshold of convection electric fields is significantly reduced by increasing the ionization rate, the realistic range of which could be estimated from observed electron energy spectra.

  8. Theory of the fine structure of auroral kilometric radiation

    Science.gov (United States)

    Grabbe, C. L.

    1982-01-01

    Recent data from ISEE 1 show auroral kilometric radiation (AKR) with finely separated bands in frequency. The observation that the AKR fine structure frequency separation is about equal to the ion cyclotron frequency at the AKR source is strong evidence for the interaction of AKR and electrostatic ion cyclotron (EIC) waves in the source, as proposed by Grabbe et al. (1980) to explain the origin of AKR. It is pointed out that no other wave of frequency close to the band separation is known to exist in the auroral source region. The fine structure observed in the source region AKR is the first evidence for EIC waves in the lower source region (3000 - 5000 km attitude), as required in the theory of Grabbe et al.

  9. Height-integrated conductivity in auroral substorms - 2. Modeling

    DEFF Research Database (Denmark)

    Gjerløv, Jesper Wittendorff; Hoffman, R.A.

    2000-01-01

    Calculations of height-integrated conductivity from 31 individual Dynamics Explorer (DE 2) substorm crossings presented by Gjerloev and Hoffman [this issue] are used to compile empirical models of the height-integrated Pedersen and Hall conductivities (conductances) in a bulge-type auroral substorm....... Global auroral images obtained by Dynamics Explorer 1 (DE 1) were used to select substorms displaying a typical bulge-type emission pattern and each individual DE 2 pass was positioned with respect to key features in the observed emission pattern. The conductances were calculated for each DE 2 pass using...... electron precipitation data and a monoenergetic conductance model. All passes were divided into six different sectors, and average conductance profiles were carefully deduced for each of these sectors. Using a simple boxcar filter, smoothed average sector passes were calculated and from linear...

  10. Asymmetric auroral intensities in the Earth's Northern and Southern hemispheres

    Science.gov (United States)

    Laundal, K. M.; Østgaard, N.

    2009-07-01

    It is commonly assumed that the aurora borealis (Northern Hemisphere) and aurora australis (Southern Hemisphere) are mirror images of each other because the charged particles causing the aurora follow the magnetic field lines connecting the two hemispheres. The particles are believed to be evenly distributed between the two hemispheres, from the source region in the equatorial plane of the magnetosphere. Although it has been shown that similar auroral features in the opposite hemispheres can be displaced tens of degree in longitude and that seasonal effects can cause differences in global intensity, the overall auroral patterns were still similar. Here we report observations that clearly contradict the common assumption about symmetric aurora: intense spots are seen at dawn in the Northern summer Hemisphere, and at dusk in the Southern winter Hemisphere. The asymmetry is interpreted in terms of inter-hemispheric currents related to seasons, which have been predicted but hitherto had not been seen.

  11. The Global Auroral Imaging Access (GAIA) VxO Program

    Science.gov (United States)

    Spanswick, E.; Donovan, E.; Syrjaesuo, M.; Kauristie, K.; Mende, S.; Frey, H.; Germany, G.; Roberts, A.; Lummerzheim, D.; Marple, S.; Honary, F.; Weatherwax, A.; Moen, J.; Manuel, J.; Sandahl, I.

    2006-12-01

    The Global Auroral Imaging Access virtual observatory (herein GAIA-VxO) is being developed as a clearing house for data related to remote sensing of auroral precipitation. GAIA-VxO is a truly international program. Researchers in Finland, the UK, Canada, and the US have agreed to contribute work on different modules of the overall GAIA system. These include summary browsers, mirror sites, and a data distribution system. GAIA will stage summary and full-resolution data from satellite-borne and ground-based auroral imagers, as well as meridian scanning photometers, and imaging and single-beam riometers. GAIA will provide ready access to data from the THEMIS, NORSTAR, and MIRACLE ASIs, as well, numerous other programs. GAIA has at its heart a relational data base, and protocols for production of summary data (we currently have more than 7,000,000 summary images on our prototype web page http://gaia-vxo.org). In this talk, we present an overview of the GAIA concept and architecture. We discuss how GAIA will draw on the efforts of researchers from different countries, with different programmatic constraints and scientific and operational objectives. Finally, we provide some insights into how GAIA will form an integral part of the evolving Living With a Star Data Environment.

  12. Effects of interplanetary shock inclinations on auroral power intensity

    CERN Document Server

    Oliveira, D M; Tsurutani, B T; Gjerloev, J W

    2015-01-01

    We derive fast forward interplanetary (IP) shock speeds and impact angles to study the geoeffectivness of 461 IP shocks that occurred from January 1995 to December 2013 using ACE and WIND spacecraft data. The geomagnetic activity is inferred from the SuperMAG project data. SuperMAG is a large chain which employs more than 300 ground stations to compute enhanced versions of the traditional geomagnetic indices. The SuperMAG auroral electroject SME index, an enhanced version of the traditional AE index, is used as an auroral power (AP) indicator. AP intensity jumps triggered by shock impacts are correlated with both shock speed and impact angle. It is found that high AP intensity events typically occur when high speed IP shocks impact the Earths magnetosphere with the shock normal almost parallel to the Sun-Earth line. This result suggests that symmetric and strong magnetospheric compression leads to favorable conditions for intense auroral power release, as shown previously by simulations and observations. Some...

  13. Effects of Interplanetary Shock Inclinations on Nightside Auroral Power Intensity

    Science.gov (United States)

    Oliveira, D. M.; Raeder, J.; Tsurutani, B. T.; Gjerloev, J. W.

    2016-02-01

    We derive fast forward interplanetary (IP) shock speeds and impact angles to study the geoeffectiveness of 461 IP shocks that occurred from January 1995 to December 2013 using ACE and Wind spacecraft data. The geomagnetic activity is inferred from the SuperMAG project data. SuperMAG is a large chain which employs more than 300 ground stations to compute enhanced versions of the traditional geomagnetic indices. The SuperMAG auroral electroject SME index, an enhanced version of the traditional AE index, is used as an auroral power (AP) indicator. AP intensity jumps triggered by shock impacts are correlated with both shock speed and impact angle. It is found that high AP intensity events typically occur when high speed IP shocks impact the Earth's magnetosphere with the shock normal almost parallel to the Sun-Earth line. This result suggests that symmetric and strong magnetospheric compression leads to favorable conditions for intense auroral power release, as shown previously by simulations and observations. Some potential mechanisms will be discussed.

  14. 3D modelling of stellar auroral radio emission

    Science.gov (United States)

    Leto, P.; Trigilio, C.; Buemi, C. S.; Umana, G.; Ingallinera, A.; Cerrigone, L.

    2016-06-01

    The electron cyclotron maser is the coherent emission process that gives rise to the radio lighthouse effect observed in the hot magnetic chemically peculiar star CU Virginis. It has also been proposed to explain the highly circularly polarized radio pulses observed in some ultracool dwarfs with spectral type earlier than M7. Coherent events of this kind resemble auroral radio emission from the magnetized planets of the Solar system. In this article, we present a three-dimensional model able to simulate the timing and profile of the pulses emitted by those stars characterized by a dipolar magnetic field by following the hypothesis of the laminar source model, used to explain the beaming of terrestrial auroral kilometric radiation. This model proves to be a powerful tool with which to understand the auroral radio emission phenomenon, allowing us to derive some general conclusions about the effects of the model's free parameters on the features of coherent pulses and to learn more about the detectability of such pulsed radio emission.

  15. Latitudinal and longitudinal dispersion of energetic auroral protons

    Directory of Open Access Journals (Sweden)

    D. A. Lorentzen

    Full Text Available Using a collision by collision model from Lorentzen et al., the latitudinal and longitudinal dispersion of single auroral protons are calculated. The proton energies varies from 1 to 50 keV, and are released into the atmosphere at 700 km altitude. The dipole magnetic field has a dip-angle of 8 degrees. Results show that the main dispersion region is at high altitudes (300-350 km and occurs during the first few charge exchange collisions. As the proton travels further down the atmosphere the mean free path becomes smaller, and as a result the spreading effect will not be as pronounced. This means that the first few charge exchange collisions fully determines the width of both the latitudinal and longitudinal dispersion. The volume emission rate was calculated for energies between 1 and 50 keV, and it was found that dayside auroral hydrogen emissions rates were approximately 10 times weaker than nightside emission rates. Simulations were also performed to obtain the dependence of the particle dispersion as a function of initial pitch-angle. It was found that the dispersion varies greatly with initial pitch-angle, and the results are summarized in two tables; a main and an extreme dispersion region.

    Key words. Ionosphere (auroral ionosphere; · particle precipitation · Space plasma physics · (transport processes

  16. E-region echo characteristics governed by auroral arc electrodynamics

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available Observations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ion-acoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.

    Key words. Ionosphere (ionospheric irregularities; electric fields and currents

  17. Imaging and EISCAT radar measurements of an auroral prebreakup event

    Directory of Open Access Journals (Sweden)

    V. Safargaleev

    Full Text Available The results of coordinated EISCAT and TV-camera observations of a prebreakup event on 15 November 1993 have been considered. The variations of the luminosity of two parallel auroral arcs, plasma depletion on the poleward edge of one of these arcs as well as electron and ion temperatures in front of a westward travelling surge were studied. It was found that a short-lived brightening of a weak zenith arc before an auroral breakup was accompanied by fading of an equatorial arc and, vice versa. A plasma depletion in the E region was detected by the EISCAT radar on the poleward edge of the zenith arc just before the auroral breakup. The plasma depletion was associated with an enhancement of ion (at the altitudes of 150–200 km and electron (in E region temperatures. During its occurrence, the electric field in the E-region was extremely large (~150 mV/m. A significant increase in ion temperature was also observed 1 min before the arrival of a westward travelling surge (WTS at the radar zenith. This was interpreted as the existence of an extended area of enhanced electric field ahead of the WTS.

  18. A hybrid simulation model for a stable auroral arc

    Directory of Open Access Journals (Sweden)

    P. Janhunen

    Full Text Available We present a new type of hybrid simulation model, intended to simulate a single stable auroral arc in the latitude/altitude plane. The ionospheric ions are treated as particles, the electrons are assumed to follow a Boltzmann response and the magnetospheric ions are assumed to be so hot that they form a background population unaffected by the electric fields that arise. The system is driven by assumed parallel electron energisation causing a primary negative charge cloud and an associated potential structure to build up. The results show how a closed potential structure and density depletion of an auroral arc build up and how they decay after the driver is turned off. The model also produces upgoing energetic ion beams and predicts strong static perpendicular electric fields to be found in a relatively narrow altitude range (~ 5000–11 000 km.

    Key words. Magnetospheric physics (magnetosphere-ionosphere interactions; auroral phenomena – Space plasma physics (numerical simulation studies

  19. 3D-modelling of the stellar auroral radio emission

    CERN Document Server

    Leto, P; Buemi, C S; Umana, G; Ingallinera, A; Cerrigone, L

    2016-01-01

    The electron cyclotron maser is the coherent emission process that gives rise to the radio lighthouse effect observed in the hot magnetic chemically peculiar star CU Virginis. It has also been proposed to explain the highly circularly polarized radio pulses observed on some ultra cool dwarfs, with spectral type earlier than M7. Such kind of coherent events resemble the auroral radio emission from the magnetized planets of the solar system. In this paper, we present a tridimensional model able to simulate the timing and profile of the pulses emitted by those stars characterized by a dipolar magnetic field by following the hypothesis of the laminar source model, used to explain the beaming of the terrestrial auroral kilometric radiation. This model proves to be a powerful tool to understand the auroral radio-emission phenomenon, allowing us to derive some general conclusions about the effects of the model's free parameters on the features of the coherent pulses, and to learn more about the detectability of such...

  20. Auroral Workshop generates U.S.-Finnish teamwork

    Science.gov (United States)

    Moldwin, Mark

    Forty scientists from the United States and Finland met last spring at a workshop to develop collaborative studies of magnetospheric-ionospheric coupling and to synthesize multiple ground-based and space-based data sets. The workshop also provided an opportunity to compare the output of new U.S. and Finnish Global Magnetohydrodynamic models with ground-based and satellite observations. Some of the missions and facilities that are providing new data within the United States and Finland include the Global Geospace Science/national Solar-Terrestrial Program Polar and Wind satellites, Interball, the Fast Auroral Snapshot Explorer, the Solar and Heliospheric Observatory, Ulysses, the Svalbard Radar, the new Super Dual Auroral Radar Network (SuperDARN) station, digital all sky cameras, and the Magnetosphere Imager (MI) array in Finland. The workshop began with a discussion of dayside magnetospheric-ionospheric coupling. Dayside ionospheric transient signatures were divided into three types: auroral forms and convection velocity spikes, magnetic and convection events, and twin convection vortices. The three classes differ in size, location, repetition rates, and Interplanetary Magnetic Field (IMF) dependencies. Scientists are addressing whether the transient classes are related, what the transients' role is compared to that of permanent cusp features, and how transients affect mag-netospheric energetics.

  1. The effects of magnetic storm phases on F-layer irregularities from auroral to equatorial latitudes

    Science.gov (United States)

    Aarons, Jules; Mendillo, Michael

    1990-12-01

    Some topics of discussion in this journal include the following: The effects of electric field and ring current energy increases on F-layer irregularities at auroral and sub-auroral latitudes; The role of the ring current in generating or inhibiting equatorial F-layer irregularities during magnetic storms; Auroral and sub-auroral F-layer irregularities and high plasma convection during the magnetically active periods of September 17-24, 1984; and Simultaneous All-Sky Optical Airglow Imaging Observations and San Marco Satellite Measurements in the Pacific Sector.

  2. Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

    Directory of Open Access Journals (Sweden)

    J. Uemoto

    2010-02-01

    Full Text Available The virtual height of the bottom side F-region (h'F and equatorial spread-F (ESF onsets at Chumphon (10.7° N, 99.4° E; 3.3° N magnetic latitude were compared with the behaviour of equatorial electrojet (EEJ ground strength at Phuket (8.1° N, 98.3° E; 0.1° N magnetic latitude during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.

  3. Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope.

    Science.gov (United States)

    Nichols, J D; Badman, S V; Baines, K H; Brown, R H; Bunce, E J; Clarke, J T; Cowley, S W H; Crary, F J; Dougherty, M K; Gérard, J-C; Grocott, A; Grodent, D; Kurth, W S; Melin, H; Mitchell, D G; Pryor, W R; Stallard, T S

    2014-05-28

    We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ∼330% rigid corotation from near ∼01 h LT toward ∼08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current.

  4. Auroral radio absorption and the westward travelling surge

    Energy Technology Data Exchange (ETDEWEB)

    Collis, P.N.; Korth, A.

    1983-11-01

    Measurements from a network of riometers during the passage of an auroral westward traveling surge are presented. These show that the energetic precipitation producing the radio absorption expands in an almost identical fashion to the softer precipitation associated with the visible surge; but it is delayed by about two minutes with respect to the surge. The delay is interpreted as a hardening of the precipitating electron spectrum as the surge goes by. Simultaneous observations of electrons at synchronous orbit are shown to support this conclusion. 24 references.

  5. Auroral phenomenology and magnetospheric processes earth and other planets

    CERN Document Server

    Keiling, Andreas; Bagenal, Fran; Karlsson, Tomas

    2013-01-01

    Published by the American Geophysical Union as part of the Geophysical Monograph Series. Many of the most basic aspects of the aurora remain unexplained. While in the past terrestrial and planetary auroras have been largely treated in separate books, Auroral Phenomenology and Magnetospheric Processes: Earth and Other Planets takes a holistic approach, treating the aurora as a fundamental process and discussing the phenomenology, physics, and relationship with the respective planetary magnetospheres in one volume. While there are some behaviors common in auroras of the diffe

  6. Height-integrated conductivity in auroral substorms. 1. Data

    DEFF Research Database (Denmark)

    Gjerløv, Jesper Wittendorff; Hoffman, R.A.

    2000-01-01

    instrument (LAPI) carried on DE 2 and the monoenergetic conductance model by Reiff [1984]. This method is shown to effectively minimize undesirable smearing of parameters in statistical substorm studies. Large spatial gradients in the conductance profiles are common in high-latitude part of the premidnight...... to select substorms which display a typical bulge-type auroral emission pattern and to organize the position of individual DE 2 passes with respect to key features in the emission pattern. The Hall and Pedersen conductances are calculated from electron precipitation data obtained by the low altitude plasma...... are common. The latitudinal conductance profiles are strongly asymmetric and have a pronounced local time dependency....

  7. A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast

    Directory of Open Access Journals (Sweden)

    J. Vassal

    Full Text Available In the framework of the French-Ivorian participation to the IEEY, a network of 10 electromagnetic stations were installed at African longitudes. The aim of this experiment was twofold: firstly, to study the magnetic signature of the equatorial electrojet on the one hand, and secondly, to characterize the induced electric field variations on the other hand. The first results of the magnetic field investigations were presented by Doumouya and coworkers. Those of the electric field experiment will be discussed in this study. The electromagnetic experiment will be described. The analysis of the electromagnetic transient variations was conducted in accordance with the classical distinction between quiet and disturbed magnetic situations. A morphological analysis of the recordings is given, taking into consideration successively quiet and disturbed magnetic situations, with the results interpreted in terms of the characterization of external and internal sources. Particular attention was paid to the effects of the source characteristics on the induced field of internal origin, and to the bias they may consequently cause to the results of electromagnetic probing of the Earth; the source effect in electromagnetic induction studies. During quiet magnetic situations, our results demonstrated the existence of two different sources. One of these, the SRE source, was responsible for most of the magnetic diurnal variation and corresponded to the well-known magnetic signature of the equatorial electrojet. The other source (the SR*E source was responsible for most of the electric diurnal variation, and was also likely to be an ionospheric source. Electric and magnetic diurnal variations are therefore related to different ionospheric sources, and interpreting the electric diurnal variation as induced by the magnetic field diurnal variation is not relevant. Furthermore, the magnetotelluric probing of the upper mantle at

  8. Day-to-day variability of Equatorial Ionization Anomaly over the Indian and Brazilian sectors - the role of Equatorial Electrojet

    Science.gov (United States)

    Kavutarapu, Venkatesh; Gende, Mauricio; Fagundes, Paulo Roberto; De Jesus, Rodolfo; Denardini, Clezio Marcos; De Abreu, Alessandro

    2016-07-01

    The equatorial electrojet (EEJ) is a narrow band of current flowing eastward at the ionospheric E-region altitudes along the dayside dip equator. Mutually perpendicular electric and magnetic fields over the equator results in the formation of Equatorial Ionization Anomaly (EIA) which in turn generates large electron density variabilities. Simultaneous study on the characteristics of EEJ and EIA is necessary to understand the role of EEJ on the EIA variabilities. Present study reports simultaneous variations of EEJ and GPS-TEC over Indian and Brazilian sectors to understand the role of EEJ on the day-to-day characteristics of the EIA. Magnetometer measurements during the low solar activity year 2004 are used to derive the EEJ values over the two different sectors. The characteristics of EIA are studied using two different chains of GPS receivers along the common meridian of 770E (India) and 450W (Brazil). The diurnal, seasonal and day-to-day variations of EEJ and TEC are described simultaneously. Variations of EIA during different seasons are presented along with the variations of the EEJ in the two hemispheres. The role of EEJ variations on the characteristic features of the EIA such as the strength and temporal extent of the EIA crest etc., have also been reported. Further, the time delay between the occurrences of the day maximum EEJ and the well-developed EIA are studied and corresponding results are presented in this paper. Further, the results from a study on the noon time bite-outs at the anomaly crest locations with their absence over the equator in the Indian and Brazilian sector are also discussed in this paper.

  9. Relationship between the lunar tidal amplification in the equatorial electrojet and weakening of the northern polar vortex

    Science.gov (United States)

    Adnan Siddiqui, Tarique; Luehr, Hermann; Stolle, Claudia; Matzka, Jürgen

    2016-07-01

    Enhanced lunar tidal effects in the equatorial electrojet (EEJ) during boreal winters have been reported in the form of so-called "big L days" for a long time. Recent studies have suggested a relation between these enhanced lunar tidal observations and stratospheric sudden warming (SSW) events in the northern hemisphere through changes in tidal propagation conditions due to increased planetary wave activity. In this study we have used the horizontal component of the magnetic field recorded at Huancayo, Peru from 1997-2013 to study the relation between the timing and magnitude of the semimonthly lunar tide in the EEJ and the stratospheric polar vortex weakening (PVW). The definition of PVW is used to characterize the individual SSW events, and the intensity of PVW during each winter is estimated by taking into account the stratospheric temperature and wind conditions at polar latitudes. Our results indicate that the semimonthly lunar tide in the EEJ gets enhanced during boreal winters when a significant weakening in the polar vortex occurs and its timing and magnitude is correlated with the timing and intensity of the PVW. Our results suggest that the initiation of the lunar tidal enhancement in most of the cases is closely related to a PVW event. Further, we also discuss the longitudinal differences in lunar tidal enhancements of the EEJ during the SSW years. Finally, we extend the lunar tidal time series by utilizing the recently digitized magnetic recordings from Huancayo. The additional data of Huancayo recordings between 1962-1984 will open new perspectives in investigating long term trends of equatorial electrodynamics.

  10. Studies of the auroral ionosphere with the MITHRAS

    Science.gov (United States)

    Foster, J. C.

    1986-06-01

    The extensive MITHRAS radar data set was the object of extensive analyses of the processes and characteristics of the auroral latitude ionosphere and thermosphere: (1) High-Latitude Electrodynamics: Ionospheric response to substorms at widely separated local times was investigated. (2) Ionospheric Plasma Transport: The effects of plasma convection on the formation of the midlatitude trough were studied utilizing the wide spatial field of view of the Millstone radar. (3) Convection Snapshots: Simultaneous data from spaced instruments were combined to produce snapshots of the polar and auroral convection pattern. (4) Comparisons with Models. (5) Data Bases Studies and Empirical Models: The extensive data set which resulted from the MITHRAS experimental program was incorporated into a multi-instrument, common format data base. (6) Azimuth Scan Experiments: Analysis of the complex data during MITHRAS azimuth scanning experiments resulted in the capability of mapping the convection electric field within the extended field of the radar. (7) Thermosphere and Exosphere: The diurnal variation of exospheric temperature over 30 degrees of latitude around Millstone Hill has been investigated using MITHRAS elevation scan data.

  11. Response of northern winter polar cap to auroral substorms

    Science.gov (United States)

    Liou, Kan; Sotirelis, Thomas

    2016-05-01

    The three-phase substorm sequence has been generally accepted and is often tied to the Dungey cycle. Although previous studies have mostly agreed on the increase and decrease in the polar cap area during an episode of substorm, there are disparate views on when the polar cap starts to contract relative to substorm onset. Here we address this conflict using high-resolution (~1-3 min) snapshot global auroral images from the ultraviolet imager on board the Polar spacecraft. On the basis of 28 auroral substorm events, all observed in the Northern Hemispheric winter, it is found that the polar cap inflated prior to onset in all events and it attained the largest area ~6 min prior to the substorm expansion phase onset, while the dayside polar cap area remained steady around the onset. The onset of nightside polar cap deflation is found to be attributed to intensifications of aurora on the poleward edge of the nightside oval, mostly in the midnight sector. Although this result supports the loading-unloading and reconnection substorm models, it is not clear if the initial polar cap deflation and the substorm expansion are parts of the same process.

  12. Radar scatter from equatorial electrojet waves: An explanation for the constancy of the Type I Doppler shift with zenith angle

    Science.gov (United States)

    Kelley, M. C.; Cuevas, R. A.; Hysell, D. L.

    2008-02-01

    The first results from the 430 MHz Advanced Modular Incoherent Scatter Radar Prototype (AMISR-P) at the Jicamarca Radio Observatory were reported by Hysell et al. (2007). We present additional data showing that the phase velocity of Type I echoes is independent of zenith angle, an unexplained property of these waves. We interpret the results using rocket data by predicting the total line-of-sight velocity at the four zenith angles used. We find that the radars preferentially detect waves within 10% of C s in at least four range gates for all beams and up to eight range gates for the 51 JULIA beam. This result is consistent with recent auroral observations that Type I waves are only generated with k vectors near the electron flow velocity, where the latter is the vector sum of the zero-order drift and the perturbation drift due to large-scale waves in the equatorial case.

  13. Simultaneous ground- and satellite-based observation of MF/HF auroral radio emissions

    Science.gov (United States)

    Sato, Yuka; Kumamoto, Atsushi; Katoh, Yuto; Shinbori, Atsuki; Kadokura, Akira; Ogawa, Yasunobu

    2016-05-01

    We report on the first simultaneous measurements of medium-high frequency (MF/HF) auroral radio emissions (above 1 MHz) by ground- and satellite-based instruments. Observational data were obtained by the ground-based passive receivers in Iceland and Svalbard, and by the Plasma Waves and Sounder experiment (PWS) mounted on the Akebono satellite. We observed two simultaneous appearance events, during which the frequencies of the auroral roar and MF bursts detected at ground level were different from those of the terrestrial hectometric radiation (THR) observed by the Akebono satellite passing over the ground-based stations. This frequency difference confirms that auroral roar and THR are generated at different altitudes across the F peak. We did not observe any simultaneous observations that indicated an identical generation region of auroral roar and THR. In most cases, MF/HF auroral radio emissions were observed only by the ground-based detector, or by the satellite-based detector, even when the satellite was passing directly over the ground-based stations. A higher detection rate was observed from space than from ground level. This can primarily be explained in terms of the idea that the Akebono satellite can detect THR emissions coming from a wider region, and because a considerable portion of auroral radio emissions generated in the bottomside F region are masked by ionospheric absorption and screening in the D/E regions associated with ionization which results from auroral electrons and solar UV radiation.

  14. MITHRAS: A Program of Simultaneous Radar Observations of the High-Latitude Auroral Zone.

    Science.gov (United States)

    1982-11-01

    CHATANIKA AND MILL - STONE HILL. The vertical arrow indicates local midnight. 29 electron densities. The nighttime minima are not as well reproduced by the... Nuit de Haute Latitude," Proceedings of GRECO Conference, Grenoble, France (September 1982). Senior, C., P. Bauer, C. Taieb, and Michel Petit, "Le R61e...Alignis, Precipitations Diffuses et Electrojets dans le Secteur Nuit de Haute Latitude," C. Senior, Proceedings of GRECO Conference, Grenoble, 1982. 0"On

  15. Radar observations of auroral zone flows during a multiple-onset substorm

    Directory of Open Access Journals (Sweden)

    J. P. Morelli

    Full Text Available We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every ~12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the pre-existing extended current system driven by the large-scale flow. These filaments are ~1 h MLT wide (~600 km, and initially expand poleward to a width of ~300 km before contracting equatorward and coalescing with the pre-existing current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50–100 m s–1 or less during the first few minutes, before surging equatorward at 0.5–1.0 km s–1 during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed ~100 mho, before decaying over a few minutes. This value compares with Hall conductivities of ~20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms.

  16. Spatial and temporal variations of small-scale plasma turbulence parameters in the equatorial electrojet: HF and VHF radar observational results

    Directory of Open Access Journals (Sweden)

    G. Manju

    2005-06-01

    Full Text Available The spatial and temporal variations of various parameters associated with plasma wave turbulence in the equatorial electrojet (EEJ at the magnetic equatorial location of Trivandrum (8.5° N, 77° E; dip 0.5° N are studied for the first time, using co-located HF (18MHz and VHF (54.95MHz coherent backscatter radar observations (daytime in the altitude region of 95-110km, mostly on magnetically quiet days. The derived turbulence parameters are the mean electron density irregularity strength (δn/n, anomalous electron collision frequency (νe* and the corrected east-west electron drift velocity (Vey. The validity of the derived parameters is confirmed using radar data at two different frequencies and comparing with in-situ measurements. The behaviour of δn/n in relation to the backscattered power during weak and strong EEJ conditions is also examined to understand the growth and evolution of turbulence in the electrojet.

  17. Investigating the effect of geomagnetic storm and equatorial electrojet on equatorial ionospheric irregularity over East African sector

    Science.gov (United States)

    Seba, Ephrem Beshir; Nigussie, Melessew

    2016-11-01

    The variability of the equatorial ionosphere is still a big challenge for ionospheric dependent radio wave technology users. To mitigate the effect of equatorial ionospheric irregularity on trans-ionospheric radio waves considerable efforts are being done to understand and model the equatorial electrodynamics and its connection to the creation of ionospheric irregularity. However, the effect of the East-African ionospheric electrodynamics on ionospheric irregularity is not yet well studied due to lack of multiple ground based instruments. But, as a result of International Heliophysical Year (IHY) initiative, which was launched in 2007, some facilities are being deployed in Africa since then. Therefore, recently deployed instruments, in the Ethiopian sector, such as SCINDA-GPS receiver (2.64°N dip angle) for TEC and amplitude scintillation index (S4) data and two magnetometers, which are deployed on and off the magnetic equator, data collected in the March equinoctial months of the years 2011, 2012, and 2015 have been used for this study in conjunction with geomagnetic storm data obtained from high resolution OMNI WEB data center. We have investigated the triggering and inhibition mechanisms for ionospheric irregularities using, scintillation index (S4), equatorial electrojet (EEJ), interplanetary electric field (IEFy), symH index, AE index and interplanetary magnetic field (IMF) Bz on five selected storm and two storm free days. We have found that when the eastward EEJ fluctuates in magnitude due to storm time induced electric fields at around noontime, the post-sunset scintillation is inhibited. All observed post-sunset scintillations in equinox season are resulted when the daytime EEJ is non fluctuating. The strength of noontime EEJ magnitude has shown direct relation with the strength of the post-sunset scintillations. This indicates that non-fluctuating EEJ stronger than 20 nT, can be precursor for the occurrence of the evening time ionospheric irregularities

  18. Simultaneous auroral observations described in the historical records of China, Japan and Korea from ancient times to AD 1700

    Directory of Open Access Journals (Sweden)

    D. M. Willis

    Full Text Available Early auroral observations recorded in various oriental histories are examined in order to search for examples of strictly simultaneous and indisputably independent observations of the aurora borealis from spatially separated sites in East Asia. In the period up to ad 1700, only five examples have been found of two or more oriental auroral observations from separate sites on the same night. These occurred during the nights of ad 1101 January 31, ad 1138 October 6, ad 1363 July 30, ad 1582 March 8 and ad 1653 March 2. The independent historical evidence describing observations of mid-latitude auroral displays at more than one site in East Asia on the same night provides virtually incontrovertible proof that auroral displays actually occurred on these five special occasions. This conclusion is corroborated by the good level of agreement between the detailed auroral descriptions recorded in the different oriental histories, which furnish essentially compatible information on both the colour (or colours of each auroral display and its approximate position in the sky. In addition, the occurrence of auroral displays in Europe within two days of auroral displays in East Asia, on two (possibly three out of these five special occasions, suggests that a substantial number of the mid-latitude auroral displays recorded in the oriental histories are associated with intense geomagnetic storms.

    Key words. Magnetospheric physics (auroral phenomena; storms and substorms

  19. Constraining Substellar Magnetic Dynamos using Auroral Radio Emission

    Science.gov (United States)

    Kao, Melodie; Hallinan, Gregg; Pineda, J. Sebastian; Escala, Ivanna; Burgasser, Adam J.; Stevenson, David J.

    2017-01-01

    An important outstanding problem in dynamo theory is understanding how magnetic fields are generated and sustained in fully convective stellar objects. A number of models for possible dynamo mechanisms in this regime have been proposed but constraining data on magnetic field strengths and topologies across a wide range of mass, age, rotation rate, and temperature are sorely lacking, particularly in the brown dwarf regime. Detections of highly circularly polarized pulsed radio emission provide our only window into magnetic field measurements for objects in the ultracool brown dwarf regime. However, these detections are very rare; previous radio surveys encompassing ˜60 L6 or later targets have yielded only one detection. We have developed a selection strategy for biasing survey targets based on possible optical and infrared tracers of auroral activity. Using our selection strategy, we previously observed six late L and T dwarfs with the Jansky Very Large Array (VLA) and detected the presence of highly circularly polarized radio emission for five targets. Our initial detections at 4-8 GHz provided the most robust constraints on dynamo theory in this regime, confirming magnetic fields >2.5 kG. To further develop our understanding of magnetic fields in the ultracool brown dwarf mass regime bridging planets and stars, we present constraints on surface magnetic field strengths for two Y-dwarfs as well as higher frequency observations of the previously detected L/T dwarfs corresponding ~3.6 kG fields. By carefully comparing magnetic field measurements derived from auroral radio emission to measurements derived from Zeeman broadening and Zeeman Doppler imaging, we provide tentative evidence that the dynamo operating in this mass regime may be inconsistent with predicted values from currently in vogue models. This suggests that parameters beyond convective flux may influence magnetic field generation in brown dwarfs.

  20. Whistler-Langmuir oscillitons and their relation to auroral hiss

    Directory of Open Access Journals (Sweden)

    K. Sauer

    2011-10-01

    Full Text Available A new type of oscilliton (soliton with superimposed spatial oscillations is described which arises in plasmas if the electron cyclotron frequency Ωe is larger than the electron plasma frequency ωe, which is a typical situation for auroral regions in planetary magnetospheres. Both high-frequency modes of concern, the Langmuir and the whistler wave, are completely decoupled if they propagate parallel to the magnetic field. However, for oblique propagation two mixed modes are created with longitudinal and transverse electric field components. The lower mode (in the literature commonly called the whistler mode, e.g. Gurnett et al., 1983 has whistler wave characteristics at small wave numbers and asymptotically transforms into the Langmuir mode. As a consequence of the coupling between these two modes, with different phase velocity dependence, a maximum in phase velocity appears at finite wave number. The occurrence of such a particular point where phase and group velocity coincide creates the condition for the existence of a new type of oscillating nonlinear stationary structure, which we call the whistler-Langmuir (WL oscilliton. After determining, by means of stationary dispersion theory, the parameter regime in which WL oscillitons exist, their spatial profiles are calculated within the framework of cold (non-relativistic fluid theory. Particle-in-cell (PIC simulations are used to demonstrate the formation of WL oscillitons which seem to play an important role in understanding electron beam-excited plasma radiation that is observed as auroral hiss in planetary magnetospheres far away from the source region.

  1. Identification of possible intense historical geomagnetic storms using combined sunspot and auroral observations from East Asia

    Directory of Open Access Journals (Sweden)

    D. M. Willis

    2005-03-01

    Full Text Available Comprehensive catalogues of ancient sunspot and auroral observations from East Asia are used to identify possible intense historical geomagnetic storms in the interval 210 BC-AD 1918. There are about 270 entries in the sunspot catalogue and about 1150 entries in the auroral catalogue. Special databases have been constructed in which the scientific information in these two catalogues is placed in specified fields. For the purposes of this study, an historical geomagnetic storm is defined in terms of an auroral observation that is apparently associated with a particular sunspot observation, in the sense that the auroral observation occurred within several days of the sunspot observation. More precisely, a selection criterion is formulated for the automatic identification of such geomagnetic storms, using the oriental records stored in the sunspot and auroral databases. The selection criterion is based on specific assumptions about the duration of sunspot visibility with the unaided eye, the likely range of heliographic longitudes of an energetic solar feature, and the likely range of transit times for ejected solar plasma to travel from the Sun to the Earth. This selection criterion results in the identification of nineteen putative historical geomagnetic storms, although two of these storms are spurious in the sense that there are two examples of a single sunspot observation being associated with two different auroral observations separated by more than half a (synodic solar rotation period. The literary and scientific reliabilities of the East Asian sunspot and auroral records that define the nineteen historical geomagnetic storms are discussed in detail in a set of appendices. A possible time sequence of events is presented for each geomagnetic storm, including possible dates for both the central meridian passage of the sunspot and the occurrence of the energetic solar feature, as well as likely transit times for the ejected solar plasma

  2. Identification of possible intense historical geomagnetic storms using combined sunspot and auroral observations from East Asia

    Science.gov (United States)

    Willis, D. M.; Armstrong, G. M.; Ault, C. E.; Stephenson, F. R.

    2005-03-01

    Comprehensive catalogues of ancient sunspot and auroral observations from East Asia are used to identify possible intense historical geomagnetic storms in the interval 210 BC-AD 1918. There are about 270 entries in the sunspot catalogue and about 1150 entries in the auroral catalogue. Special databases have been constructed in which the scientific information in these two catalogues is placed in specified fields. For the purposes of this study, an historical geomagnetic storm is defined in terms of an auroral observation that is apparently associated with a particular sunspot observation, in the sense that the auroral observation occurred within several days of the sunspot observation. More precisely, a selection criterion is formulated for the automatic identification of such geomagnetic storms, using the oriental records stored in the sunspot and auroral databases. The selection criterion is based on specific assumptions about the duration of sunspot visibility with the unaided eye, the likely range of heliographic longitudes of an energetic solar feature, and the likely range of transit times for ejected solar plasma to travel from the Sun to the Earth. This selection criterion results in the identification of nineteen putative historical geomagnetic storms, although two of these storms are spurious in the sense that there are two examples of a single sunspot observation being associated with two different auroral observations separated by more than half a (synodic) solar rotation period. The literary and scientific reliabilities of the East Asian sunspot and auroral records that define the nineteen historical geomagnetic storms are discussed in detail in a set of appendices. A possible time sequence of events is presented for each geomagnetic storm, including possible dates for both the central meridian passage of the sunspot and the occurrence of the energetic solar feature, as well as likely transit times for the ejected solar plasma. European telescopic

  3. Rocket-borne investigation of auroral patches in the evening sector during substorm recovery

    Directory of Open Access Journals (Sweden)

    M. A. Danielides

    Full Text Available On 11 February 1997 at 08:36 UT after a substorm onset the Auroral Turbulence 2 sounding rocket was launched from Poker Flat Research Range, Alaska into a moderately active auroral region. This experiment has allowed us to investigate evening (21:00 MLT auroral forms at the substorm recovery, which were discrete multiple auroral arcs stretched to, the east and southeast from the breakup region, and bright auroral patches propagating westward along the arcs like a luminosity wave, which is a typical feature of the disturbed arc. The rocket crossed an auroral arc of about 40 km width, stretched along southeast direction. Auroral patches and associated electric fields formed a 200 km long periodical structure, which propagated along the arc westward at a velocity of 3 km/s, whereas the ionospheric plasma velocity inside the arc was 300 m/s westward. The spatial periodicity in the rocket data was found from optical ground-based observations, from electric field in situ measurements, as well as from ground-based magnetic observations. The bright patches were co-located with equatorward plasma flow across the arc of the order of 200 m/s in magnitude, whereas the plasma flow tended to be poleward at the intervals between the patches, where the electric field reached the magnitude of up to 20 mV/m, and these maxima were co-located with the peaks in electron precipitations indicated by the electron counter on board the rocket. Pulsations of a 70-s period were observed on the ground in the eastern component of the magnetic field and this is consistent with the moving auroral patches and the north-south plasma flows associated with them. The enhanced patch-associated electric field and fast westward propagation suggest essential differences between evening auroral patches and those occurring in the morning ionosphere. We propose the wave that propagates along the plasma sheet boundary to be a promising mechanism for the evening auroral patches

  4. Plasma physics on auroral field lines - The formation of ion conic distributions

    Science.gov (United States)

    Ashour-Abdalla, M.; Okuda, H.

    1983-01-01

    The formation of the conical distribution function and the acceleration of ions on aurora field lines are considered. Ion cyclotron waves were assumed to be excited by drifting electrons associated with the return current in the auroral zone. A theoretical analysis of ion cyclotron waves is given, and a simulation model is described. Simulation results are presented. The heating of ions and the evolution of ion cyclotron waves on auroral field lines and in the magnetosphere are discussed.

  5. Self-excitation of auroral arcs in a three-dimensionally coupled magnetosphere-ionosphere system

    Science.gov (United States)

    Watanabe, Kunihiko; Sato, Tetsuya

    1988-01-01

    This paper presents the first full three-dimensional dynamic simulation of auroral arc formation. The magnetospheric and ionospheric dynamics are represented by one-fluid magnetohydrodynamic equations and two-fluid weakly ionized plasma equations, respectively. The feedback coupling between magnetospheric Alfven waves and ionospheric density waves results in a spontaneous generation of longitudinally elongated striations of field-aligned currents and ionospheric electron densities, which compare very well with many features of quiet auroral arcs.

  6. Features of Pc5 pulsations in the geomagnetic field, auroral luminosity, and Riometer absorption

    Science.gov (United States)

    Belakhovsky, V. B.; Pilipenko, V. A.; Samsonov, S. N.; Lorentsen, D.

    2016-01-01

    Simultaneous morning Pc5 pulsations ( f ~ 3-5 mHz) in the geomagnetic field, aurora intensities (in the 557.7 and 630.0 nm oxygen emissions and the 471.0 nm nitrogen emission), and riometer absorption, were studied based on the CARISMA, CANMOS, and NORSTAR network data for the event of January 1, 2000. According to the GOES-8 satellite observations, these Pc5 geomagnetic pulsations are observed as incompressible Alfvén waves with toroidal polarization in the magnetosphere. Although the Pc5 pulsation frequencies in auroras, the geomagnetic field, and riometer absorption are close to one another, stable phase relationships are not observed between them. Far from all trains of geomagnetic Pc5 pulsations are accompanied by corresponding auroral pulsations; consequently, geomagnetic pulsations are primary with respect to auroral pulsations. Both geomagnetic and auroral pulsations propagate poleward, and the frequency decreases with increasing geomagnetic latitude. When auroral Pc5 pulsations appear, the ratio of the 557.7/630.0 nm emission intensity sharply increases, which indicates that auroral pulsations result from not simply modulated particle precipitation but also an additional periodic acceleration of auroral electrons by the wave field. A high correlation is not observed between Pc5 pulsations in auroras and the riometer absorption, which indicates that these pulsations have a common source but different generation mechanisms. Auroral luminosity modulation is supposedly related to the interaction between Alfvén waves and the region with the field-aligned potential drop above the auroral ionosphere, and riometer absorption modulation is caused by the scattering of energetic electrons by VLF noise pulsations.

  7. Accaleration of Electrons of the Outer Electron Radiation Belt and Auroral Oval Dynamics

    Science.gov (United States)

    Antonova, Elizaveta; Ovchinnikov, Ilya; Riazantseva, Maria; Znatkova, Svetlana; Pulinets, Maria; Vorobjev, Viachislav; Yagodkina, Oksana; Stepanova, Marina

    2016-07-01

    We summarize the results of experimental observations demonstrating the role of auroral processes in the formation of the outer electron radiation belt and magnetic field distortion during magnetic storms. We show that the auroral oval does not mapped to the plasma sheet proper (region with magnetic field lines stretched in the tailward direction). It is mapped to the surrounding the Earth plasma ring in which transverse currents are closed inside the magnetosphere. Such currents constitute the high latitude continuation of the ordinary ring current. Mapping of the auroral oval to the region of high latitude continuation of the ordinary ring current explains the ring like shape of the auroral oval with finite thickness near noon and auroral oval dynamics during magnetic storms. The auroral oval shift to low latitudes during storms. The development of the ring current produce great distortion of the Earth's magnetic field and corresponding adiabatic variations of relativistic electron fluxes. Development of the asymmetric ring current produce the dawn-dusk asymmetry of such fluxes. We analyze main features of the observed processes including formation of sharp plasma pressure profiles during storms. The nature of observed pressure peak is analyzed. It is shown that the observed sharp pressure peak is directly connected with the creation of the seed population of relativistic electrons. The possibility to predict the position of new radiation belt during recovery phase of the magnetic storm using data of low orbiting and ground based observations is demonstrated.

  8. On a theory of temporal fluctuations in the electrostatic potential structures associated with auroral arcs

    Science.gov (United States)

    Silevitch, M. B.

    1981-01-01

    A possible mechanism is presented for the generation of large-amplitude temporal fluctuations in the structure of the electron energization region associated with auroral arcs. The mechanism is based on the observation that the auroral arc system resembles a laboratory circuit consisting of the series connection of battery, resistance and a forward biased diode containing collisionless plasma in which large-amplitude relaxation oscillations are sometimes observed to be superimposed on the steady-state current. It is shown that in both the laboratory and auroral systems, in which a localized auroral arc dynamo, the ionosphere and the electron energization region are involved, the oscillations are controlled by the times for ions and electrons to traverse the acceleration region, which also characterize the low- and high-frequency structure of the fluctuating waveform. It is demonstrated that a plausible one-dimensional double-layer model of the auroral arc acceleration region exhibits the dynamic negative resistance necessary for the generation of oscillations by the present mechanism. Finally, consideration is given to two kinds of auroral phenomena which might be associated with the mechanism: the 10-Hz quasi-periodic flickering aurora and 10-Hz modulations in the intensity of electrostatic hydrogen cyclotron waves.

  9. Severe and localized GNSS scintillation at the poleward edge of the nightside auroral oval during intense substorm aurora

    CERN Document Server

    van der Meeren, Christer; Lorentzen, Dag A; Rietveld, Michael T; Clausen, Lasse B N

    2016-01-01

    In this paper we study how GPS, GLONASS, and Galileo navigation signals are compromised by strong irregularities causing severe phase scintillation ($\\mathit{\\sigma }_{\\phi }$ > 1) in the nightside high-latitude ionosphere during a substorm on 3 November 2013. Substorm onset and a later intensification coincided with polar cap patches entering the auroral oval to become auroral blobs. Using Global Navigation Satellite Systems (GNSS) receivers and optical data, we show severe scintillation driven by intense auroral emissions in the line of sight between the receiver and the satellites. During substorm expansion, the area of scintillation followed the intense poleward edge of the auroral oval. The intense auroral emissions were colocated with polar cap patches (blobs). The patches did not contain strong irregularities, neither before entering the auroral oval nor after the aurora had faded. Signals from all three GNSS constellations were similarly affected by the irregularities. Furthermore, two receivers space...

  10. Temporal and spatial evolution of discrete auroral arcs as seen by Cluster

    Science.gov (United States)

    Figueiredo, S.; Marklund, G. T.; Karlsson, T.; Johansson, T.; Ebihara, Y.; Ejiri, M.; Ivchenko, N.; Lindqvist, P.-A.; Nilsson, H.; Fazakerley, A.

    2005-10-01

    Two event studies are presented in this paper where intense convergent electric fields, with mapped intensities up to 1350 mV/m, are measured in the auroral upward current region by the Cluster spacecraft, at altitudes between 3 and 5 Earth radii. Both events are from May 2003, Southern Hemisphere, with equatorward crossings by the Cluster spacecraft of the pre-midnight auroral oval. Event 1 occurs during the end of the recovery phase of a strong substorm. A system of auroral arcs associated with convergent electric field structures, with a maximum perpendicular potential drop of about ~10 kV, and upflowing field-aligned currents with densities of 3 µA/m2 (mapped to the ionosphere), was detected at the boundary between the Plasma Sheet Boundary Layer (PSBL) and the Plasma Sheet (PS). The auroral arc structures evolve in shape and in magnitude on a timescale of tens of minutes, merging, broadening and intensifying, until finally fading away after about 50 min. Throughout this time, both the PS region and the auroral arc structure in its poleward part remain relatively fixed in space, reflecting the rather quiet auroral conditions during the end of the substorm. The auroral upward acceleration region is shown for this event to extend beyond 3.9 Earth radii altitude. Event 2 occurs during a more active period associated with the expansion phase of a moderate substorm. Images from the Defense Meteorological Satellite Program (DMSP) F13 spacecraft show that the Cluster spacecraft crossed the horn region of a surge-type aurora. Conjugated with the Cluster spacecraft crossing above the surge horn, the South Pole All Sky Imager recorded the motion and the temporal evolution of an east-west aligned auroral arc, 30 to 50 km wide. Intense electric field variations are measured by the Cluster spacecraft when crossing above the auroral arc structure, collocated with the density gradient at the PS poleward boundary, and coupled to intense upflowing field-aligned currents with

  11. Reformed Solitary Kinetic Alfvén Waves due to Dissipations and Auroral Electron Acceleration

    Institute of Scientific and Technical Information of China (English)

    WU De-Jin; CHAO Jih-Kwin; LEE Luo-Chuan; FENG Xue-Shang

    2001-01-01

    The physical nature of the auroral electron acceleration has been an outstanding problem in space physics for decades.Some recent observations from the auroral orbit satellites,FREJA and FAST,showed that large amplitude solitary kinetic Alfvén waves (SKAWs) are a common electromagnetic active phenomenon in the auroral magnetosphere. In a Iow-ββ/2 (i.e.,β/2 < me/mi < 1) plasma,the drift velocity of electrons relative to ions within SKAWs is much larger than thermal velocities of both electrons and ions.This leads to instabilities and causes dissipations of SKAWs.In the present work,based on the analogy of classical particle motion in a potential well,it is shown that a shock-like structure can be formed from SKAWs if dissipation effects are included.The reformed SKAWs with a shock-like structure have a local density jump and a net field-aligned electric potential drop of order of mev2A/e over a characteristic width of several )e.As a consequence,the reformed SKAWs can efficiently accelerate electrons field-aligned to the order of the local Alfvén velocity.In particular,we argue that this electron acceleration mechanism by reformed SKAWs can play an important role in the auroral electron acceleration problem.The result shows that not only the location of acceleration regions predicted by this model is well consistent with the observed auroral electron acceleration region of I 2 RE above the auroral ionosphere,but also the accelerated electrons from this region can obtain an energy of several keV and carry a field-aligned current of several/A/m2 which are comparable to the observations of auroral electrons.

  12. MITHRAS studies of the auroral oval and polar cap

    Science.gov (United States)

    Delabeaujardiere, Odile; Watermann, Juergen; Johnson, Robert M.

    1991-01-01

    MITHRAS is a program of coordinated experiments dedicated to studying the coupling between the magnetosphere, the ionosphere, and the thermosphere. MITHRAS observations mostly involve the Sondrestrom radar in Greenland, but other incoherent scatter radars around the world were also used. Contract highlights include the following items. (1) The most extensive comparisons ever made between incoherent scatter radar data and numerical simulation models were performed. These comparisons were based on both individual case studies and averaged data, and included observations from all the incoherent scatter radars. The comparisons showed general agreement between observations and model calculations but they also showed significant differences. (2) During solar maximum conditions, the contribution to the height integrated Pederson conductivity from solar produced F-region ionization can be as large as 60 pct. of the total. (3) Under certain geophysical conditions it appears possible to identify the low altitude cusp and distinguish it from the cleft. The cusp proper appears to be characterized by enhanced F region plasma density collocated with elevated F region electron temperature; it does not appear to be associated with a particular plasma flow pattern signature. (4) A new mechanism was proposed to explain how auroral surges might be formed. It was suggested that the surge was associated with a distortion of the poleward boundary of the aurora, and that this distortion was caused by the field aligned current.

  13. Ionospheric current system accompanied by auroral vortex streets

    CERN Document Server

    Hiraki, Yasutaka

    2016-01-01

    High resolution optical measurements have revealed that a sudden brightening of aurora and its deformation from an arc-like to a vortex street structure appear just at the onset of substorm. The instability of Alfv$\\acute{\\rm e}$n waves reflected from the ionosphere has been studied by means of magnetohydrodynamic simulations in order to comprehend the formation of auroral vortex streets. Our previous work reported that an initially placed arc intensifies, splits, and deforms into a vortex street during a couple of minutes, and the prime key is an enhancement of the convection electric field. This study elaborated physics of the ionospheric horizontal currents related to the vortex street in the context of so-called Cowling polarization. One component is due to the perturbed electric field by Alfv$\\acute{\\rm e}$n waves, and the other is due to the perturbed electron density (or polarization) in the ionosphere. It was found that, when a vortex street develops, upward/downward pair currents in its leading/trail...

  14. Langmuir turbulence in the auroral ionosphere 1: Linear theory

    Science.gov (United States)

    Newman, D. L.; Goldman, M. V.; Ergun, R. E.; Boehm, M. H.

    1994-01-01

    Intense bursts of Langmuir waves with electric fields of 50 to 500 mV / m have been frequently observed at altitudes greater than 500 km in the auroral ionosphere. These bursts are driven by 20 eV to 4 keV field-aligned electrons, which are embedded in an approximately isotropic nonthermal tail of scattered electrons. The Langmuir bursts are often observed at altitudes where the ionosphere is moderately magnetized (OMEGA (sub e) approximately equals omega (sub pe)). Both the moderate magnetization and the scattered electrons have a major influence on the linear dispersion and damping of Langmuir waves. In particular, the linear dispersion is topologically different depending on whether the magnetic field is subcritical (OMEGA (sub e) less than omega (sub pe)) or supercritical (OMEGA (sub e) greater than omega (sub pe)). The correct dispersion and damping can account for the observed polarization of the Langmuir waves, which is very nearly parallel to the geomagnetic field. Inferred properties of the linear instability driven by the field-aligned electrons are discussed. The linear dispersion and damping derived here provide the basis for a nonlinear turbulence study described in a companion paper (Newman et al., this issue).

  15. Effects of auroral potential drops on plasma sheet dynamics

    Science.gov (United States)

    Xi, Sheng; Lotko, William; Zhang, Binzheng; Wiltberger, Michael; Lyon, John

    2016-11-01

    The reaction of the magnetosphere-ionosphere system to dynamic auroral potential drops is investigated using the Lyon-Fedder-Mobarry global model including, for the first time in a global simulation, the dissipative load of field-aligned potential drops in the low-altitude boundary condition. This extra load reduces the field-aligned current (j||) supplied by nightside reconnection dynamos. The system adapts by forcing the nightside X line closer to Earth, with a corresponding reduction in current lensing (j||/B = constant) at the ionosphere and additional contraction of the plasma sheet during substorm recovery and steady magnetospheric convection. For steady and moderate solar wind driving and with constant ionospheric conductance, the cross polar cap potential and hemispheric field-aligned current are lower by approximately the ratio of the peak field-aligned potential drop to the cross polar cap potential (10-15%) when potential drops are included. Hemispheric ionospheric Joule dissipation is less by 8%, while the area-integrated, average work done on the fluid by the reconnecting magnetotail field increases by 50% within |y| < 8 RE. Effects on the nightside plasma sheet include (1) an average X line 4 RE closer to Earth; (2) a 12% higher mean reconnection rate; and (3) dawn-dusk asymmetry in reconnection with a 17% higher rate in the premidnight sector.

  16. Juno's Earth flyby: the Jovian infrared Auroral Mapper preliminary results

    Science.gov (United States)

    Adriani, A.; Moriconi, M. L.; Mura, A.; Tosi, F.; Sindoni, G.; Noschese, R.; Cicchetti, A.; Filacchione, G.

    2016-08-01

    The Jovian InfraRed Auroral Mapper, JIRAM, is an image-spectrometer onboard the NASA Juno spacecraft flying to Jupiter. The instrument has been designed to study the aurora and the atmosphere of the planet in the spectral range 2-5 μm. The very first scientific observation taken with the instrument was at the Moon just before Juno's Earth fly-by occurred on October 9, 2013. The purpose was to check the instrument regular operation modes and to optimize the instrumental performances. The testing activity will be completed with pointing and a radiometric/spectral calibrations shortly after Jupiter Orbit Insertion. Then the reconstruction of some Moon infrared images, together with co-located spectra used to retrieve the lunar surface temperature, is a fundamental step in the instrument operation tuning. The main scope of this article is to serve as a reference to future users of the JIRAM datasets after public release with the NASA Planetary Data System.

  17. Statistical study of the GNSS phase scintillation associated with two types of auroral blobs

    Science.gov (United States)

    Jin, Yaqi; Moen, Jøran I.; Miloch, Wojciech J.; Clausen, Lasse B. N.; Oksavik, Kjellmar

    2016-05-01

    This study surveys space weather effects on GNSS (Global Navigation Satellite System) signals in the nighttime auroral and polar cap ionosphere using scintillation receivers, all-sky imagers, and the European Incoherent Scatter Svalbard radar. We differentiate between two types of auroral blobs: blob type 1 (BT 1) which is formed when islands of high-density F region plasma (polar cap patches) enter the nightside auroral oval, and blob type 2 (BT 2) which are generated locally in the auroral oval by intense particle precipitation. For BT 1 blobs we have studied 41.4 h of data between November 2010 and February 2014. We find that BT 1 blobs have significantly higher scintillation levels than their corresponding polar cap patch; however, there is no clear relationship between the scintillation levels of the preexisting polar cap patch and the resulting BT 1 blob. For BT 2 blobs we find that they are associated with much weaker scintillations than BT 1 blobs, based on 20 h of data. Compared to patches and BT 2 blobs, the significantly higher scintillation level for BT 1 blobs implies that auroral dynamics plays an important role in structuring of BT 1 blobs.

  18. GPS scintillation effects associated with polar cap patches and substorm auroral activity: direct comparison

    Directory of Open Access Journals (Sweden)

    Jin Yaqi

    2014-01-01

    Full Text Available We directly compare the relative GPS scintillation levels associated with regions of enhanced plasma irregularities called auroral arcs, polar cap patches, and auroral blobs that frequently occur in the polar ionosphere. On January 13, 2013 from Ny-Ålesund, several polar cap patches were observed to exit the polar cap into the auroral oval, and were then termed auroral blobs. This gave us an unprecedented opportunity to compare the relative scintillation levels associated with these three phenomena. The blobs were associated with the strongest phase scintillation (σϕ, followed by patches and arcs, with σϕ up to 0.6, 0.5, and 0.1 rad, respectively. Our observations indicate that most patches in the nightside polar cap have produced significant scintillations, but not all of them. Since the blobs are formed after patches merged into auroral regions, in space weather predictions of GPS scintillations, it will be important to enable predictions of patches exiting the polar cap.

  19. Auroral radio absorption as an indicator of magnetospheric electrons and of conditions in the disturbed auroral D-region

    Energy Technology Data Exchange (ETDEWEB)

    Collis, P.N.; Hargreaves, J.K. (Lancaster Univ. (UK)); Korth, A. (Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau (Germany, F.R.))

    1984-01-01

    In a previous paper we demonstrated a method by which the auroral radio absorption measured with a riometer can be predicted from energetic electron measurements at geosynchronous orbit. The present paper enquires to what extent the process can be inverted: what levels of magnetospheric electron flux, and of D-region production rate, electron density and incremental absorption, are predicted by a given measurement of radio absorption and what reliance can be placed on such predictions. Using data from 45 precipitation features recorded with riometers in Scandinavia and at geosynchronous orbit with GEOS-2, it is shown that electron fluxes in the ranges 20 to 40, 40 to 80 and 80 to 160 keV increase with increasing absorption and can be predicted to better than 50% for absorption events of 2 dB or greater. Electrons above 160 keV show little or no correlation with absorption. D-region production rates and electron densities can be predicted to within factors of 2 and square root of 2, respectively. It is more difficult to specify the height of the absorbing region because of uncertainty in the profile of the effective recombination coefficient. Having regard to other data, an ..cap alpha..sub(eff) profile is proposed which satisfies rocket and incoherent scatter data as well as the present calculations.

  20. Use of the Auroral Boundary Index for potential forecasting of ionospheric scintillation

    Science.gov (United States)

    Griffin, James M.; Connor, Thomas C.; Snell, Hilary E.

    2012-01-01

    The Hardy-Gussenhoven Auroral Dosing Model (HGADM) was developed to compute electron characteristic energy and energy flux values onto the global grid and is often used to generate the inputs for other phenomenological models. Forecasting auroral conditions is limited by rapid changes in the ionosphere due to variable solar conditions. However, through a statistical analysis of Auroral Boundary Index data we have developed a technique which allows us to forecast/predict the appropriate inputs to the HGADM, thereby providing a means of forecasting the characteristic energy and energy flux values. This paper will initially discuss the statistical analysis and the development of the forecast mode for the HGADM. We then discuss the possibility that aurora-based indices along with other environmental indicators can be correlated to ionospheric disturbances.

  1. Acceleration of hydrogen ions and conic formation along auroral field lines

    Energy Technology Data Exchange (ETDEWEB)

    Okuda, H.; Ashour-Abdalla, M.

    1982-05-01

    Electrostatic ion cyclotron turbulence and the formation of ion conics at low altitudes (approx. = 1500 km) along auroral field lines have been investigated analytically and by plasma numerical simulations. Ion cyclotron waves are assumed to be driven unstable by the up-going cold ionospheric electrons associated with the downward auroral current. When the electron drift speed is comparable to the electron thermal speed, it is found that the large amplitude, e phi/T/sub e/ approx. = 1, coherent, ..omega.. = ..cap omega../sub i/, ion cyclotron waves shoudl exist along auroral field lines at low altitudes extending approx. = 500 to 1000 km. Ion conics are associated with the cyclotron turbulence and the ion bulk temperature is found to increase a factor of 10 of the initial ionospheric temperature, while the temperature of the high energy tail can be as much as a factor of 100 of the ionospheric temperature. Theory and simulations agree well.

  2. Nonlinear interactions of electromagnetic waves with the auroral ionosphere

    Science.gov (United States)

    Wong, Alfred Y.

    1999-09-01

    The ionosphere provides us with an opportunity to perform plasma experiments in an environment with long confinement times, very large-scale lengths, and no confining walls. The auroral ionosphere with its nearly vertical magnetic field geometry is uniquely endowed with large amount of free energy from electron and ion precipitation along the magnetic field and mega-ampere current across the magnetic field. To take advantage of this giant outdoor laboratory, two facilities HAARP and HIPAS, with frequencies ranging from the radio to optical bands, are now available for active probing of and interaction with this interesting region. The ponderomotive pressures from the self-consistent wave fields have produced significant local perturbations of density and particle distributions at heights where the incident EM frequency matches a plasma resonance. This paper will review theory and experiments covering the nonlinear phenomena of parametric decay instability to wave collapse processes. At HF frequencies plasma lenses can be created by preconditioning pulses to focus what is a normally divergent beam into a high-intensity spot to further enhance nonlinear phenomena. At optical wavelengths a large rotating liquid metal mirror is used to focus laser pulses up to a given height. Such laser pulses are tuned to the same wavelengths of selected atomic and molecular resonances, with resulting large scattering cross sections. Ongoing experiments on dual-site experiments and excitation of ELF waves will be presented. The connection of such basic studies to environmental applications will be discussed. Such applications include the global communication using ELF waves, the ozone depletion and remediation and the control of atmospheric CO2 through the use of ion cyclotron resonant heating.

  3. Current-voltage relationship in the auroral particle acceleration region

    Directory of Open Access Journals (Sweden)

    M. Morooka

    2004-11-01

    Full Text Available The current-voltage relationship in the auroral particle acceleration region has been studied statistically by the Akebono (EXOS-D satellite in terms of the charge carriers of the upward field-aligned current. The Akebono satellite often observed field-aligned currents which were significantly larger than the model value predicted by Knight (1973. We compared the upward field-aligned current estimated by three different methods, and found that low-energy electrons often play an important role as additional current carriers, together with the high-energy primary electrons which are expected from Knight's relation. Such additional currents have been observed especially at high and middle altitudes of the particle acceleration region. Some particular features of electron distribution functions, such as "cylindrical distribution functions" and "electron conics", have often been observed coinciding with the additional currents. They indicated time variability of the particle acceleration region. Therefore, we have concluded that the low-energy electrons within the "forbidden" region of electron phase space in the stationary model often contribute to charge carriers of the current because of the rapid time variability of the particle acceleration region. "Cylindrical distribution functions" are expected to be found below the time-varying potential difference. We statistically examined the locations of "cylindrical distribution function", and found that their altitudes are related to the location where the additional currents have been observed. This result is consistent with the idea that the low-energy electrons can also carry significant current when the acceleration region changes in time.

  4. Velocity of small-scale auroral ionospheric current systems over Indian Antarctic station Maitri

    Indian Academy of Sciences (India)

    Girija Rajaram; A N Hanchinal; R Kalra; K Unnikrishnan; K Jeeva; M Sridharan; A Dhar

    2002-03-01

    The Indian Antarctic station Maitri (geog. 70° 45/S, 11° 45/E, geom. 66° .03S, 53°.21E) occupies a sub-auroral location during magnetically quiet conditions ( Kp < 10), but attains an auroral position when the auroral oval shifts equatorwards with increasing strength of magnetic disturbance. At the latter times, triangulation with 3 uxgate magnetometers located at the vertices of a suitable triangle provides a means of monitoring mobile auroral ionospheric current systems over Maitri. The spacing between the magnetometers is typically kept at 75-200 km, keeping in mind the scale-sizes of ∼100 km for these mobile current systems. This work reports the results of two triangulation experiments carried out around Maitri in January 1992 and January 1995, both during Antarctic summer. The velocities estimated for pulsations of the Pc4 and Pc5 type were about 0.59 km/sec in the direction 102°.7 east of due north, in the first case, and about 1-3 km/sec in the second case in the east-west direction. While several magnetometer arrays exist in the northern auroral regions (e.g., the Alberta array in Canada, the Alaskan array in the U.S. and the IMS Scandinavian array), there is no report in literature of triangulation through arrays in Antarctica, except for a one-day study by Neudegg et al 1995 for ULF pulsations of the Pc1 and Pc2 type. The velocities obtained for the Pi3 type of irregular pulsations over Antarctica in the present study tally well with those obtained for northern auroral locations.

  5. THEMIS ground-space observations during the development of auroral spirals

    Directory of Open Access Journals (Sweden)

    A. Keiling

    2009-11-01

    Full Text Available A simultaneous observation of an auroral spiral and its generator region in the near-Earth plasma sheet is rather unlikely. Here we present such observations using the THEMIS spacecraft as well as the THEMIS ground network of all-sky imagers and magnetometers. Two consecutive auroral spirals separated by approximately 14 min occurred during a substorm on 19 February 2008. The spirals formed during the expansion phase and a subsequent intensification, and were among the brightest features in the aurora with diameters of 200–300 km. The duration for the formation and decay of each spiral was less than 60 s. Both spirals occurred shortly after the formation of two oppositely rotating plasma flow vortices in space, which were also accompanied by dipolarizations and ion injections, at ~11 RE geocentric distance. Observations and model calculations also give evidence for a magnetic-field-aligned current generation of approximately 0.1 MA via the flow vortices, connecting the generator region of the spirals with the ionosphere, during the formation of both spirals. In the ionosphere, a pair of equivalent ionospheric current (EIC vortices with opposite rotations (corresponding to upward and downward currents was present during both auroral spirals with enhanced EICs and ionospheric flows at the locations of the auroral spirals and along the auroral arcs. The combined ground and space observations suggest that each auroral spiral was powered by two oppositely rotating plasma flow vortices that caused a current enhancement in the substorm current wedge.

  6. Synoptical Auroral Ovals: A Comparison study with TIMED/GUVI Observations

    Science.gov (United States)

    Liou, K.; Paxton, L.; Zhang, Y.

    2007-12-01

    Whether the aurora Australis is a mirror image of its northern hemispheric counterpart is a question that auroral physicists have been wanting to answer. Owing to geophysical constraints, especially the large offset between the location of the southern magnetic and southern geographic poles, there is a paucity of information about the aurora Australis. Comparisons of some instantansous global-scale northern and southern auroras acquired conjugately by Polar and IMAGE spacecraft recently have shown mixed results. In this study, we present data from a different source to provide insight into the global morphology and behavior of the auroral oval. Approximately 20,000 Earth's disk FUV images acquired from the Global Ultraviolet Imager (GUVI) on-board NASA's Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite between February 2002 and February 2006 are processed and analyzed. Synoptic auroral distributions for the northern and southern ovals are derived. Our study result reveals that the statistical oval is nearly hemispherically symmetric (within ±80%). Several known features in the morphology of the aurora Borealis are also observed in the Southern Hemisphere: For instance, the auroral midday gap and the premidnight maximum. The hemispherical symmetry of the auroras deteriorates as the partition of solar illumination in the two hemisphere polar region becomes asymmetric. It is estimated that the solar illumination effect accounts for up to ~50% of the hemispheric asymmetry. We found evidence that suggests that the aurora is suppressed under sunlit conditions in the South just as it is in the North. We also found that the auroral energy flux increases monotonically with the increase of the solar zenith angle. These results suggest that ionospheric conductivity plays an active role in regulating magnetospheric energy deposition in the auroral zone.

  7. Multi-Camera Reconstruction of Fine Scale High Speed Auroral Dynamics

    Science.gov (United States)

    Hirsch, M.; Semeter, J. L.; Zettergren, M. D.; Dahlgren, H.; Goenka, C.; Akbari, H.

    2014-12-01

    The fine spatial structure of dispersive aurora is known to have ground-observable scales of less than 100 meters. The lifetime of prompt emissions is much less than 1 millisecond, and high-speed cameras have observed auroral forms with millisecond scale morphology. Satellite observations have corroborated these spatial and temporal findings. Satellite observation platforms give a very valuable yet passing glance at the auroral region and the precipitation driving the aurora. To gain further insight into the fine structure of accelerated particles driven into the ionosphere, ground-based optical instruments staring at the same region of sky can capture the evolution of processes evolving on time scales from milliseconds to many hours, with continuous sample rates of 100Hz or more. Legacy auroral tomography systems have used baselines of hundreds of kilometers, capturing a "side view" of the field-aligned auroral structure. We show that short baseline (less than 10 km), high speed optical observations fill a measurement gap between legacy long baseline optical observations and incoherent scatter radar. The ill-conditioned inverse problem typical of auroral tomography, accentuated by short baseline optical ground stations is tackled with contemporary data inversion algorithms. We leverage the disruptive electron multiplying charge coupled device (EMCCD) imaging technology and solve the inverse problem via eigenfunctions obtained from a first-principles 1-D electron penetration ionospheric model. We present the latest analysis of observed auroral events from the Poker Flat Research Range near Fairbanks, Alaska. We discuss the system-level design and performance verification measures needed to ensure consistent performance for nightly multi-terabyte data acquisition synchronized between stations to better than 1 millisecond.

  8. Magnetosheath density fluctuations from a simulation of auroral kilometric radiation radio propagation

    Energy Technology Data Exchange (ETDEWEB)

    Steinberg, J.L.; Hoang, S. [Observatoire de Paris, Meudon (France)

    1993-08-01

    Here the authors use a ray tracing technique to map the appearance of the image of auroral kilometric radiation (AKR), originating above the auroral zone, as seen by a distant observer between 0200 and 0800 LT, at distances of 50 to 250 R{sub E}. It has been suggested that distant imaging of AKR may provide a way of imaging structures in the earths magnetosphere. They use satellite measurements to constrain the size and characteristics of the AKR source region, and their projections provide results consistent with data recorded by the ISEE-3 satellite.

  9. Auroral spectrograph data annals of the international geophysical year, v.25

    CERN Document Server

    Carrigan, Anne; Norman, S J

    1964-01-01

    Annals of the International Geophysical Year, Volume 25: Auroral Spectrograph Data is a five-chapter text that contains tabulations of auroral spectrograph data. The patrol spectrograph built by the Perkin-Elmer Corporation for the Aurora and Airglow Program of the IGY is a high-speed, low-dispersion, automatic instrument designed to photograph spectra of aurora occurring along a given magnetic meridian of the sky. Data from each spectral frame were recorded on an IBM punched card. The data recorded on the cards are printed onto the tabulations in this volume. These tabulations are available

  10. Prospect of China's Auroral Fine-structure Imaging System (CAFIS) at Zhongshan station in Antarctica

    Institute of Scientific and Technical Information of China (English)

    LIU Shun-lin; HAN De-sheng; HU Hong-qiao; HUANG De-hong; ZHANG Bei-chen; YANG Hui-gen

    2008-01-01

    A new auroral imaging system is reported which is planned to be deployed at Zhongshan Station in Antarctica in the end of 2009. The system will focus on study of optical auroras in small scales and be called China' s Auroral Fine-structure Imaging System (CAFIS). The project of CAFIS is carried out by support of 'the tenth five-year plan for capacity building' of China. CAFIS will be a powerful groundbased platform for aurora observational experiments. Composing and advantages of CAFIS are introduced in this brief report. Some potential study topics involved CAFIS are also considered.

  11. Resonant electron diffusion as a saturation process of the synchrotron maser instability. [of auroral kilometric radiation

    Science.gov (United States)

    Lee, M. C.; Kuo, S. P.

    1986-01-01

    The theory of resonant electron diffusion as an effective saturation process of the auroral kilometric radiation has been formulated. The auroral kilometric radiation is assumed to be amplified by the synchrotron maser instability that is driven by an electron distribution of the loss-cone type. The calculated intensity of the saturated radiation is found to have a significantly lower value in comparison with that caused by the quasi-linear diffusion process as an alternative saturation process. This indicates that resonant electron diffusion dominates over quasi-linear diffusion in saturating the synchrotron maser instability.

  12. The color ratio-intensity relation in the Jovian aurora: Hubble observations of auroral components

    Science.gov (United States)

    Gérard, J.-C.; Bonfond, B.; Grodent, D.; Radioti, A.

    2016-10-01

    Spectral observations made with the long slit of the Space Telescope Imaging Spectrograph (STIS) on board Hubble have been used to construct spectral maps of the FUV Jovian aurora. They reveal that the amount of absorption by overlying methane shows significant spatial variations. In this report, we examine the relationship between the auroral brightness of the unabsorbed H2 emission that is proportional to the precipitated electron energy flux, and the ultraviolet color ratio, a proxy of the mean electron energy. We find that it varies significantly between the different components of the aurora and in the polar region. Although no global dependence can be found, we show that the two quantities are better organized in some auroral components such as regions of the main aurororal emission. By contrast, the dependence of the electron characteristic energy in high-latitude and diffuse aurora regions on the auroral energy input is generally more scattered. We conclude that the various auroral components are associated with different electron acceleration processes, some of which are not governed by a simple relation linking the value of a field-aligned acceleration potential with the parallel currents flowing from the ionosphere.

  13. Auroral research at the Tromsø Northern Lights Observatory: the Harang directorship, 1928-1946

    Science.gov (United States)

    Egeland, Alv; Burke, William J.

    2016-03-01

    The Northern Lights Observatory in Tromsø began as Professor Lars Vegard's dream for a permanent facility in northern Norway, dedicated to the continuous study of auroral phenomenology and dynamics. Fortunately, not only was Vegard an internationally recognized spectroscopist, he was a great salesman and persuaded the Rockefeller Foundation that such an observatory represented an important long-term investment. A shrewd judge of talent, Vegard recognized the scientific and managerial skills of Leiv Harang, a recent graduate from the University of Oslo, and recommended that he become the observatory's first director. In 1929, subsequent to receiving the Rockefeller Foundation grant, the University of Oslo established a low temperature laboratory to support Vegard's spectroscopic investigations. This paper follows the scientific accomplishments of observatory personnel during the 18 years of Harang's directorship. These include: identifying the chemical sources of auroral emissions, discovering the Vegard-Kaplan bands, quantifying height distributions of different auroral forms, interpreting patterns of magnetic field variations, remotely probing auroral electron distribution profiles in the polar ionosphere, and monitoring the evolving states of the ozone layer. The Rockefeller Foundation judges got it right: the Tromsø Nordlysobservatoriet was, and for decades remained, an outstanding scientific investment.

  14. Space Weather Impacts on Spacecraft Design and Operations in Auroral Charging Environments

    Science.gov (United States)

    Minow, Joseph I.; Parker, Linda N.

    2012-01-01

    Spacecraft in low altitude, high inclination (including sun-synchronous) orbits are widely used for remote sensing of the Earth s land surface and oceans, monitoring weather and climate, communications, scientific studies of the upper atmosphere and ionosphere, and a variety of other scientific, commercial, and military applications. These systems are episodically exposed to environments characterized by a high flux of energetic (approx.1 to 10 s kilovolt) electrons in regions of very low background plasma density which is similar in some ways to the space weather conditions in geostationary orbit responsible for spacecraft charging to kilovolt levels. While it is well established that charging conditions in geostationary orbit are responsible for many anomalies and even spacecraft failures, to date there have been relatively few such reports due to charging in auroral environments. This presentation first reviews the physics of the space environment and its interactions with spacecraft materials that control auroral charging rates and the anticipated maximum potentials that should be observed on spacecraft surfaces during disturbed space weather conditions. We then describe how the theoretical values compare to the observational history of extreme charging in auroral environments and discuss how space weather impacts both spacecraft design and operations for vehicles on orbital trajectories that traverse auroral charging environments.

  15. Auroral arc as an electric discharge between the ionosphere and magnetosphere

    Energy Technology Data Exchange (ETDEWEB)

    Lyatskij, V.B. (AN SSSR, Kol' skij Filial. Polyarnyj Geofizicheskij Inst.)

    A new method of generation of arcs of aurora borealis is suggested. The potential difference, applied across the magnetosphere in the region of longtitudinal currents flowing from the ionosphere, brings about the periodic dependence of the electric field on the distance. Longtitudinal currents, in this case, are split into several parallel layers, which can be identical to auroral arcs.

  16. Comparison of techniques to determine intermittency of riometer auroral absorption at South Pole

    Science.gov (United States)

    Ovalle, E. M.; Stepanova, M.; Foppiano, A. J.

    2008-05-01

    It is well known that auroral radio wave absorption, as measured by riometers, consists of periods of relative quiescence which are interrupted by short bursts of activity. Such patterns in activity are observed in systems ranging from the stock market to turbulence, i.e. they exhibit intermittency. In the case of the auroral absorption it has also been found that intermittency strongly depends on the magnetic local time, being largest in the nighttime sector. This can be interpreted as indicating that the precipitating particles responsible of the absorption exhibit intermittency, especially near the substorm eye, where the level of turbulence increases. Here, different techniques to determine intermittency of auroral absorption measured by a riometer at South Pole (-90°S) are compared. The techniques are (i) the standard Castings formulation, (ii) the Local Intermittency Measure, (iii) the superstatistic, and (iv) the non-extensive statistics. It is shown that results obtained using the superstatistic and non-extensive statistic techniques confirm previously published results for auroral absorption at South Pole using the Castings and the Local Intermittency Measure techniques. Furthermore, a preliminary comparison between techniques indicates technique differences seem to be more related to the conceptual approach of each one rather than to the numerical results given by them.

  17. Solar and auroral evidence for an intense recurrent geomagnetic storm during December in AD 1128

    Energy Technology Data Exchange (ETDEWEB)

    Willis, D.M. [Warwick Univ., Coventry (United Kingdom). Dept. of Physics; Stephenson, F.R. [Durham Univ. (United Kingdom). Dept. of Physics

    2001-03-01

    The earliest known drawing of sunspots appears in The Chronicle of John of Worcester, which was compiled in the first half of the twelfth century. In this medieval chronicle, the Latin text describing the sunspots is accompanied by a colourful drawing, albeit idealised, which shows the apparent positions and sizes of two sunspots on the solar disk. The date of this observation of sunspots from Worcester, England is firmly established as AD 1128 December 8. Assuming that the drawing was prepared fairly carefully, the angular diameters of the two sunspots are at least about 3 arcmin and 2 arcmin in the northern and southern hemispheres, respectively. Similarly, the heliographic latitudes of both sunspots are within the approximate range of 25 -35 . About five days after this observation of sunspots on the solar disk, on the night of AD 1128 December 13, a red auroral display was observed from Songdo, Korea (the modern city of Kaesong). This auroral observation was recorded in the Koryo-sa, the official Korean chronicle of the period. In addition, five Chinese and five Korean descriptions of auroral displays were recorded in various East-Asian histories between the middle of AD 1127 and the middle of AD 1129. The ten oriental auroral records in this particular interval correspond to six distinct auroral events, which provide evidence for recurrent, though possibly intermittent, auroral activity on a timescale almost exactly equal to the synodic-solar-rotation period (approximately 27 days). The six distinct auroral events were apparently associated with two series of recurrent geomagnetic storms, both of which were sufficiently intense to produce mid-latitude auroral displays in East Asia. These ancient solar and auroral observations are interpreted in terms of present-day understanding of solar-terrestrial physics. Contemporary ground-based and satellite measurements during the last few decades have indicated that recurrent geomagnetic storms are usually a feature of

  18. Temporal and spatial evolution of discrete auroral arcs as seen by Cluster

    Directory of Open Access Journals (Sweden)

    S. Figueiredo

    2005-10-01

    Full Text Available Two event studies are presented in this paper where intense convergent electric fields, with mapped intensities up to 1350 mV/m, are measured in the auroral upward current region by the Cluster spacecraft, at altitudes between 3 and 5 Earth radii. Both events are from May 2003, Southern Hemisphere, with equatorward crossings by the Cluster spacecraft of the pre-midnight auroral oval.

    Event 1 occurs during the end of the recovery phase of a strong substorm. A system of auroral arcs associated with convergent electric field structures, with a maximum perpendicular potential drop of about ~10 kV, and upflowing field-aligned currents with densities of 3 µA/m2 (mapped to the ionosphere, was detected at the boundary between the Plasma Sheet Boundary Layer (PSBL and the Plasma Sheet (PS. The auroral arc structures evolve in shape and in magnitude on a timescale of tens of minutes, merging, broadening and intensifying, until finally fading away after about 50 min. Throughout this time, both the PS region and the auroral arc structure in its poleward part remain relatively fixed in space, reflecting the rather quiet auroral conditions during the end of the substorm. The auroral upward acceleration region is shown for this event to extend beyond 3.9 Earth radii altitude.

    Event 2 occurs during a more active period associated with the expansion phase of a moderate substorm. Images from the Defense Meteorological Satellite Program (DMSP F13 spacecraft show that the Cluster spacecraft crossed the horn region of a surge-type aurora. Conjugated with the Cluster spacecraft crossing above the surge horn, the South Pole All Sky Imager recorded the motion and the temporal evolution of an east-west aligned auroral arc, 30 to 50 km wide. Intense electric field variations are measured by the Cluster spacecraft when crossing above the auroral arc structure, collocated with the

  19. Observational evidence for the plausible linkage of Equatorial Electrojet (EEJ electric field variations with the post sunset F-region electrodynamics

    Directory of Open Access Journals (Sweden)

    V. Sreeja

    2009-11-01

    Full Text Available The paper is based on a detailed observational study of the Equatorial Spread F (ESF events on geomagnetically quiet (Ap≤20 days of the solar maximum (2001, moderate (2004 and minimum (2006 years using the ionograms and magnetograms from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip lat ~0.5° N in India. The study brings out some interesting aspects of the daytime Equatorial Electrojet (EEJ related electric field variations and the post sunset F-region electrodynamics governing the nature of seasonal characteristics of the ESF phenomena during these years. The observed results seem to indicate a plausible linkage of daytime EEJ related electric field variations with pre-reversal enhancement which in turn is related to the occurrence of ESF. These electric field variations are shown to be better represented through a parameter, termed as "E", in the context of possible coupling between the E- and F-regions of the ionosphere. The observed similarities in the gross features of the variations in the parameter "E" and the F-region vertical drift (Vz point towards the potential usage of the EEJ related parameter "E" as an useful index for the assessment of Vz prior to the occurrence of ESF.

  20. The Third General Scientific Assembly of the International Association of Geomagnetism and Aeronomy - Special sessions of auroral processes

    Science.gov (United States)

    Russell, C. T.

    1978-01-01

    Methods of timing magnetic substorms, the rapid fluctuations of aurorae, electromagnetic and electrostatic instabilities observed on the field lines of aurorae, the auroral microstructure, and the relationship of currents, electric field and particle precipitation to auroral form are discussed. Attention is given to such topics as D-perturbations as an indicator of substorm onset, the role of the magnetotail in substorms, spectral information derived from imaging data on aurorae, terrestrial kilometric radiation, and the importance of the mirror force in self-consistent models of particle fluxes, currents and potentials on auroral field lines.

  1. Energy deposition and non-equilibrium infared radiation of energetic auroral electrons

    Science.gov (United States)

    Wu, Yadong; Gao, Bo; Zhu, Guangsheng; Li, Ziguang

    2016-07-01

    Infrared radiation caused by energetic auroral electrons plays an important role in the thermospheric hear budget, and may be seen as background by infrared surveillance sensors. The auroral electron deposition leads to the ionization, excitation, and dissociation of neutral species(N2,O2,and O), and initiates a series of chemical reaction in the upper atmosphere, finally causes the optical emission of infared excited emitters. In this study, the whole progress from the initial auroral electrons energy deposition to the final infrared emissions has been modeled, which including space plasma, atmospheric physical chemistry, and radiative transfer. The initial atmosphere parameters before auroral disturbing are given by MSIS00 model. The primary electron flux at the top of atmosphere is given by a statistical fitting with the sum of three distribution terms, a power law, a Maxwellian and a Guassian. A semi-emprical model is used in the calculation of energy depositon of single primary electron. The total integral ion pairs production rate is obtained after combining with the initial primary electron flux. The production rate and flux of secondary electrons are modeled with a continuous slow down approximation, using different excitation, ionization, dissociation cross sections of N2, O2, and O to electrons. The photochemical reactions with auroral disturbance is analysed, and its calculation model is established. A "three-step" calculation method is created to obtain number densities of eleven species in the hight between 90-160 km, which containing N2+, O2+, O+, O2+(a4Π), O+(2D), O+(2P), N2(A3Σ), N(2D), N(4S), NO+, and N+. Number densities of different vibraional levels of NO and NO+ are got with steady state assumption, considering 1-12 vibrational levels of NO and 1-14 vibrational levels of NO+. The infared emissions and the spectral lines of the two radiating bodies are calculated with a fuzzy model of spectral band.

  2. Lower thermospheric wind variations in auroral patches during the substorm recovery phase

    Science.gov (United States)

    Oyama, Shin-ichiro; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Hosokawa, Keisuke; Watkins, Brenton J.; Kurihara, Junichi; Tsuda, Takuo T.; Fallen, Christopher T.

    2016-04-01

    Measurements of the lower thermospheric wind with a Fabry-Perot interferometer (FPI) at Tromsø, Norway, found the largest wind variations in a night during the appearance of auroral patches at the substorm recovery phase. Taking into account magnetospheric substorm evolution of plasma energy accumulation and release, the largest wind amplitude at the recovery phase is a fascinating result. The results are the first detailed investigation of the magnetosphere-ionosphere-thermosphere coupled system at the substorm recovery phase using comprehensive data sets of solar wind, geomagnetic field, auroral pattern, and FPI-derived wind. This study used three events in November 2010 and January 2012, particularly focusing on the wind signatures associated with the auroral morphology, and found three specific features: (1) wind fluctuations that were isolated at the edge and/or in the darker area of an auroral patch with the largest vertical amplitude up to about 20 m/s and with the longest oscillation period about 10 min, (2) when the convection electric field was smaller than 15 mV/m, and (3) wind fluctuations that were accompanied by pulsating aurora. This approach suggests that the energy dissipation to produce the wind fluctuations is localized in the auroral pattern. Effects of the altitudinal variation in the volume emission rate were investigated to evaluate the instrumental artifact due to vertical wind shear. The small electric field values suggest weak contributions of the Joule heating and Lorentz force processes in wind fluctuations. Other unknown mechanisms may play a principal role at the recovery phase.

  3. Substorm associated radar auroral surges: a statistical study and possible generation model

    Directory of Open Access Journals (Sweden)

    B. A. Shand

    Full Text Available Substorm-associated radar auroral surges (SARAS are a short lived (15–90 minutes and spatially localised (~5° of latitude perturbation of the plasma convection pattern observed within the auroral E-region. The understanding of such phenomena has important ramifications for the investigation of the larger scale plasma convection and ultimately the coupling of the solar wind, magnetosphere and ionosphere system. A statistical investigation is undertaken of SARAS, observed by the Sweden And Britain Radar Experiment (SABRE, in order to provide a more extensive examination of the local time occurrence and propagation characteristics of the events. The statistical analysis has determined a local time occurrence of observations between 1420 MLT and 2200 MLT with a maximum occurrence centred around 1700 MLT. The propagation velocity of the SARAS feature through the SABRE field of view was found to be predominately L-shell aligned with a velocity centred around 1750 m s–1 and within the range 500 m s–1 and 3500 m s–1. This comprehensive examination of the SARAS provides the opportunity to discuss, qualitatively, a possible generation mechanism for SARAS based on a proposed model for the production of a similar phenomenon referred to as sub-auroral ion drifts (SAIDs. The results of the comparison suggests that SARAS may result from a similar geophysical mechanism to that which produces SAID events, but probably occurs at a different time in the evolution of the event.

    Key words. Substorms · Auroral surges · Plasma con-vection · Sub-auroral ion drifts

  4. Nonlinear model of short-scale electrodynamics in the auroral ionosphere

    Directory of Open Access Journals (Sweden)

    J.-M. A. Noël

    Full Text Available The optical detection of auroral subarcs a few tens of m wide as well as the direct observation of shears several m/s per m over km to sub km scales by rocket instrumentation both indicate that violent and highly localized electrodynamics can occur at times in the auroral ionosphere over scales 100 m or less in width. These observations as well as the detection of unstable ion-acoustic waves observed by incoherent radars along the geomagnetic field lines has motivated us to develop a detailed time-dependent two-dimensional model of short-scale auroral electrodynamics that uses current continuity, Ohm's law, and 8-moment transport equations for the ions and electrons in the presence of large ambient electric fields to describe wide auroral arcs with sharp edges in response to sharp cut-offs in precipitation (even though it may be possible to describe thin arcs and ultra-thin arcs with our model, we have left such a study for future work. We present the essential elements of this new model and illustrate the model's usefulness with a sample run for which the ambient electric field is 100 mV/m away from the arc and for which electron precipitation cuts off over a region 100 m wide. The sample run demonstrates that parallel current densities of the order of several hundred µA m-2 can be triggered in these circumstances, together with shears several m/s per m in magnitude and parallel electric fields of the order of 0.1 mV/m around 130 km altitude. It also illustrates that the local ionospheric properties like densities, temperature and composition can strongly be affected by the violent localized electrodynamics and vice-versa.

    Key words: Ionosphere (auroral ionosphere, electric fields and currents, ionosphere-magnetosphere interactions

  5. Nightside auroral zone and polar cap ion outflow as a function of substorm size and phase

    Science.gov (United States)

    Wilson, G. R.; Ober, D. M.; Germany, G. A.; Lund, E. J.

    2004-02-01

    Because the high latitude ionosphere is an important source of plasma for the magnetosphere under active conditions, we have undertaken a study of the way ion outflow from the nightside auroral zone and polar cap respond to substorm activity. We have combined data from the Ultraviolet Imager (UVI) on Polar with ion upflow measurements from the TEAMS instrument on the FAST spacecraft to construct a picture of ion upflow from these regions as a function of substorm size and as a function of time relative to substorm onset. We use data taken during solar minimum in the northern hemisphere between December 1996 and February 1997. We find that the total nightside auroral zone ion outflow rate (averaged over substorm phase) depends on the size of the substorm, increasing by about a factor of 10 for both O+ and H+ from the smallest to the largest substorms in our study. The combined outflow rate from both the polar cap and the nightside auroral zone goes up by a factor of 7 for both ions for the same change in conditions. Regardless of storm size, the nightside auroral zone outflow rate increases by about a factor of 2 after onset, reaching its peak level after about 20 min. These results indicate that the change in the nightside auroral zone ion outflow rate that accompanies substorm onset is not as significant as the change from low to high magnetic activity. As a consequence, the prompt increase in the near earth plasma sheet energy density of O+ and H+ ions that accompanies onset [, 1996] is likely due to local energization of ions already present rather than to the sudden arrival and energization of fresh ionospheric plasma.

  6. The variation of Io's auroral footprint brightness with the location of Io in the plasma torus

    Science.gov (United States)

    Serio, Andrew W.; Clarke, John T.

    2008-09-01

    Ultraviolet and near-infrared observations of auroral emissions from the footprint of Io's magnetic Flux Tube (IFT) mapping to Jupiter's ionosphere have been interpreted via a combination of the unipolar inductor model [Goldreich, P., Lynden-Bell, D., 1969. Astrophys. J. 156, 59-78] and the multiply-reflected Alfvén wave model [ Belcher, J.W., 1987. Science 238, 170-176]. While both models successfully explain the general nature of the auroral footprint and corotational wake, and both predict the presence of multiple footprints, the details of the interaction near Io are complicated [ Saur, J., Neubauer, F.M., Connerney, J.E.P., Zarka, P., Kivelson, M.G., 2004. In: Bagenal, F., Dowling, T.E., McKinnon, W.B. (Eds.), Jupiter: The Planet, Satellites and Magnetosphere. Cambridge University Press, Cambridge, UK, pp. 537-560; Kivelson, M.G., Bagenal, F., Kurth, W.S., Neubauer, F.M., Paranicas, C., Saur, J., 2004. In: Bagenal, F., Dowling, T.E., McKinnon, W.B. (Eds.), Jupiter: The Planet, Satellites and Magnetosphere. Cambridge University Press, Cambridge, UK, pp. 513-536]. The auroral footprint brightness is believed to be a good remote indicator of the strength of the interaction near Io, indicating the energy and current strength linking Io with Jupiter's ionosphere. The brightness may also depend in part on local auroral acceleration processes near Jupiter. The relative importance of different physical processes in this interaction can be tested as Jupiter's rotation and Io's orbital motion shift Jupiter's magnetic centrifugal equator past Io, leading to longitudinal variations in the plasma density near Io and functionally different variations in the local field strength near Jupiter where the auroral emissions are produced. Initial HST WFPC2 observations found a high degree of variability in the footprint brightness with time, and some evidence for systematic variations with longitude [Clarke, J.T., Ben Jaffel, L., Gérard, J.-C., 1998. J. Geophys. Res. 103, 20217

  7. A real-time hybrid aurora alert system: Combining citizen science reports with an auroral oval model

    Science.gov (United States)

    Case, N. A.; Kingman, D.; MacDonald, E. A.

    2016-06-01

    Accurately predicting when, and from where, an aurora will be visible is particularly difficult, yet it is a service much desired by the general public. Several aurora alert services exist that attempt to provide such predictions but are, generally, based upon fairly coarse estimates of auroral activity (e.g., Kp or Dst). Additionally, these services are not able to account for a potential observer's local conditions (such as cloud cover or level of darkness). Aurorasaurus, however, combines data from the well-used, solar wind-driven, OVATION Prime auroral oval model with real-time observational data provided by a global network of citizen scientists. This system is designed to provide more accurate and localized alerts for auroral visibility than currently available. Early results are promising and show that over 100,000 auroral visibility alerts have been issued, including nearly 200 highly localized alerts, to over 2000 users located right across the globe.

  8. Possible relationship between the equatorial electrojet (EEJ) and daytime vertical E × B drift velocities in F region from ROCSAT observations

    Science.gov (United States)

    Kumar, Sandeep; Veenadhari, B.; Tulasi Ram, S.; Su, S.-Y.; Kikuchi, T.

    2016-10-01

    The vertical E × B drift is very important parameter as its day to day variability has great influence on the variability in the low latitude F-region ion and electron density distributions. The measurements of vertical ion velocity from the first Republic of China Satellite (ROCSAT-1) provide a unique data base for the development of possible relationship between vertical E × B drifts and ground based magnetometer observation. An attempt has been made to derive quantitative relationship between F-region vertical E × B drifts measured by ROCSAT-1 (600 km) and ground measured equatorial electrojet for the solar maximum period 2001-2003 for Indian and Japanese sectors. The results consistently indicate existence of linear relationship between the measured vertical E × B drifts at topside F-region and EEJ for both the sectors, with a moderate to high correlation coefficients. The linear relationship between ROCSAT-1 measured E × B drifts and EEJ for Indian and Japanese sectors has been compared with a similar relationship with Jicamarca Unattended Long-term Ionosphere Atmosphere Radar (JULIA) measured E × B drifts (150 km echos) and EEJ strength from Peruvian sector during 2003. It has been found that ROCSAT-1 measured E × B drifts shows linear relationship with EEJ, however, exhibits a larger scatter unlike JULIA radar observed E × B drifts. This may be attributed to the large height difference as ROCSAT-1 measures E × B drifts at 600 km altitude and the EEJ is E-region (110 km) phenomenon.

  9. Cluster observations and theoretical identification of broadband waves in the auroral region

    Directory of Open Access Journals (Sweden)

    M. Backrud-Ivgren

    2005-12-01

    Full Text Available Broadband waves are common on auroral field lines. We use two different methods to study the polarization of the waves at 10 to 180 Hz observed by the Cluster spacecraft at altitudes of about 4 Earth radii in the nightside auroral region. Observations of electric and magnetic wave fields, together with electron and ion data, are used as input to the methods. We find that much of the wave emissions are consistent with linear waves in homogeneous plasma. Observed waves with a large electric field perpendicular to the geomagnetic field are more common (electrostatic ion cyclotron waves, while ion acoustic waves with a large parallel electric field appear in smaller regions without suprathermal (tens of eV plasma. The regions void of suprathermal plasma are interpreted as parallel potential drops of a few hundred volts.

  10. Identification of the poleward boundary of the auroral oval using characteristics of ion precipitation

    Energy Technology Data Exchange (ETDEWEB)

    Troshichev, O.A.; Shishkina, E.M. [Arctic and Antartic Research Institute, St. Petersburg (Russian Federation); Meng, C.I.; Newell, P.T. [Johns Hopkins Univ., Laurel, MD (United States)

    1996-03-01

    The authors look for characteristics to identify the poleward edge of the auroral oval, by looking at precipitation properties of electrons and ions from DMSP F6 and F7 crossings of this region. They average the readings over 1/2 degree in latitude, and normalize them to flux maxima for each pass. The precipitation data clearly indicates the presence of the auroral oval. As one moves poleward then dependent upon the interplanetary magnetic field orientation, the precipitation falls off one or more orders of magnitude when B{sub z}>0, or when B{sub z}<0, it degenerates to an unstructured type of polar rain, with no clear ion precipitation evident. For B{sub z}>0 there are clear markers for identifying the inner edge of the oval, which are not so evident for southward fields. They discuss the significance of this boundary layer.

  11. "Unusual Rainbow and White Rainbow" A new auroral candidate in oriental historical sources

    CERN Document Server

    Hayakawa, Hisashi; Kawamura, Akito Davis; Tamazawa, Harufumi; Miyahara, Hiroko; Kataoka, Ryuho

    2016-01-01

    Solar activity has been recorded as auroras or sunspots in various historical sources. These records are of much importance for investigating both long-term solar activities and extremely intense solar flares. In previous studies, they were recorded as "vapor," "cloud," or "light," especially in oriental historical sources; however, the terminology was not discussed adequately and is still quite vague. In this paper, we suggest the possibility of "unusual rainbow" and "white rainbow" as candidates of historical auroras in oriental historical sources and examine if it is probable. This discovery will help us to make more comprehensive historical auroral catalogues and require us to add these terms to auroral candidates in oriental historical sources.

  12. APIS : a value-added database of HST UV planetary auroral observations acquired since 1997

    Science.gov (United States)

    Lamy, L.; Henry, F.; Prangé, R.; Le Sidaner, P.

    2014-04-01

    The APIS service http://lesia.obspm.fr/apis/ (Auroral Planetary Imaging and Spectroscopy), aimed at facilitating the use of planetary auroral observations, was presented at EPSC last year, following its opening to the community in July 2013. This facility consists of : - a high level database derived from public Far-UV observations of Jupiter, Io, Ganymede, Saturn, Titan and Uranus acquired by the Hubble Space Telescope since 1997 (36 observational campaigns so far) ; - a specific search interface (Figure 1), aimed at browsing the database freely, quickly and efficiently through relevant search criteria (as planetary longitudes, moon or spacecraft ephemeris etc.). - Virtual-Observatory tools which enable the user to interactively work with images and spectra online. We will present the updated capabilities of APIS and illustrate them with several examples. Several tutorials are also directly available online.

  13. Investigation of Io's auroral hiss emissions due to its motion in Jupiter's magnetosphere

    Institute of Scientific and Technical Information of China (English)

    Mohsen H. Moghimi

    2012-01-01

    The left-hand side of the auroral hiss emission observed by Galileo has a frequency time profile shaped very similar to the funnel shape observed in the Earth's auroral region.This close similarity indicates that we can use the theory of whistlermode propagation near the resonance cone to locate the emission source.The general characteristics of the whistler mode are discussed.Then the position of the emission source is investigated using a geometrical method that takes into account the trajectory of Galileo.Initially a point source is assumed.Then the possibility of a sheet source aligned along the magnetic field lines which are tangent to the surface of Io is investigated.Both types of sources show that the whistler mode radiation originates very close to the surface of Io.

  14. Right-hand polarized 4fce auroral roar emissions: 2. Nonlinear generation theory

    Science.gov (United States)

    Yoon, P. H.; LaBelle, J.; Weatherwax, A. T.

    2016-08-01

    Auroral roar emissions are commonly interpreted as Z (or upper hybrid) mode naturally excited by precipitating auroral electrons. Subsequent conversion to escaping radiation makes it possible for these emissions to be detected on the ground. Most emissions are detected as having left-hand (L) circular (or ordinary O) polarization, but the companion paper presents a systematic experimental study on the rare occurrence of the right-hand polarized, or equivalently, extraordinary (X) mode 4fce emission. A similar observation was reported earlier by Sato et al. (2015). The suggested emission mechanism is the nonlinear coalescence of two upper hybrid roars at 2fce. The present paper formulates a detailed theory for such an emission mechanism.

  15. Auroral displays near the 'foot' of the field line of the ATS-5 satellite

    Science.gov (United States)

    Akasofu, S.-I.; Deforest, S.; Mcilwain, C.

    1974-01-01

    Summary of an extensive correlative study of ATS-5 particle and magnetic field data with all-sky photographs from Great Whale River which is near the 'foot' of the field lines passing through the ATS-5 satellite. In particular, an effort is made to identify specific particle features with specific auroral displays during substorms, such as a westward traveling surge, poleward expansive motion, and drifting patches. It is found that, in early evening hours, the first encounter of ATS-5 with hot plasma is associated with the equatorward shift of the diffuse aurora, but not necessarily with westward traveling surges (even when the satellite is embedded in the plasma sheet). In the midnight sector, an injection corresponds very well to the initial brightening of an auroral arc. Specific features of morning sector auroras are difficult to correlate with specific particle features.

  16. The far-ultraviolet main auroral emission at Jupiter. Pt. 1. Dawn-dusk brightness asymmetries

    Energy Technology Data Exchange (ETDEWEB)

    Bonfond, B.; Gustin, J.; Gerard, J.C.; Grodent, D.; Radioti, A. [Liege Univ. (Belgium). Lab. de Physique Atmospherique et Planetaire; Palmaerts, B. [Liege Univ. (Belgium). Lab. de Physique Atmospherique et Planetaire; Max-Planck-Institut fuer Sonnensystemforschung, Goettingen (Germany); Badman, S.V. [Lancaster Univ. (United Kingdom). Dept. of Physics; Khurana, K.K. [California Univ., Los Angeles, CA (United States); Tao, C. [Institut de Recherche en Astrophysique et Planetologie, Toulouse (France)

    2015-07-01

    The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range, is related to corotation enforcement currents in the middle magnetosphere. Early models for these currents assumed axisymmetry, but significant local time variability is obvious on any image of the Jovian aurorae. Here we use far-UV images from the Hubble Space Telescope to further characterize these variations on a statistical basis. We show that the dusk side sector is ∝ 3 times brighter than the dawn side in the southern hemisphere and ∝ 1:1 brighter in the northern hemisphere, where the magnetic anomaly complicates the interpretation of the measurements.We suggest that such an asymmetry between the dawn and the dusk sectors could be the result of a partial ring current in the nightside magnetosphere.

  17. Investigation of Io's Auroral Hiss Emissions Due To Its Motion in Jupiter's Magnetosphere

    CERN Document Server

    Moghimi, M H

    2011-01-01

    The left-hand side of the auroral hiss emission observed by Galileo has a frequency time shaped very similar to the funnel shape observed in the earth's auroral region. This close similarity indicates that we can use the whistler-mode propagation near resonance cone to locate the emission source. In this paper the general characteristic of the whistler mode are discussed. Then the position of the emission source has been investigated using a geometry method that takes into account the Galileo's trajectory. Initially it is assumed the source is a point. Then the possibility of sheet source aligned along the magnetic field lines which are tangent to the surface of Io is investigated. Both of two types of sources show that the whistler mode radiation originates very close to the surface of the Io.

  18. Contributions to the Science Modeling Requirements Document; Earth Limb & Auroral Backgrounds

    Science.gov (United States)

    2007-11-02

    composition information. All models give these parameters as functions of altitude. Depending on its sophistication, a model may also report these...magnetospheric forcing (Huguenin et al., 1989; Wohlers et al., 1989). Malkmus et al. (1989) con- structed a limb clutter model for the middle ultraviolet (0.2...taken once per orbit (-100 — EL & A Bkgds, 35— Table 4-5a AURORAL ALERT SUMMARY — 1 Item Description Schedule Access Preliminary Report & Forecast

  19. The cyclotron maser theory of AKR and Z-mode radiation. [Auroral Kilometric Radiation

    Science.gov (United States)

    Wu, C. S.

    1985-01-01

    The cyclotron maser mechanism which may be responsible for the generation of auroral kilometric radiation and Z-mode radiation is discussed. Emphasis is placed on the basic concepts of the cyclotron maser theory, particularly the relativistic effect of the cyclotron resonance condition. Recent development of the theory is reviewed. Finally, the results of a computer simulation study which helps to understand the nonlinear saturation of the maser instability are reported.

  20. Electron dispersion events in the morningside auroral zone and their relationship with VLF emissions

    Science.gov (United States)

    Hardy, David A.; Burke, William J.; Villalon, Elena

    1990-05-01

    This paper reports on observations of electron precipitation bursts observed in the morningside auroral zone with the J sensor, an electron detector aboard the Hilat satellite. The characteristics of these precipitation events are documented, and a theoretical explanation that could account for the observed properties is presented. According to this model, the dispersion events result from impulsive interactions of the electrons with intense asymmetric packets of VLF waves via the nonlinear ponderomotive force.

  1. Dayside convection and auroral morphology during an interval of northward interplanetary magnetic field

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available We investigate the dayside auroral dynamics and ionospheric convection during an interval when the interplanetary magnetic field (IMF had predominantly a positive Bz component (northward IMF but varying By. Polar UVI observations of the Northern Hemisphere auroral emission indicate the existence of a region of luminosity near local noon at latitudes poleward of the dayside auroral oval, which we interpret as the ionospheric footprint of a high-latitude reconnection site. The large field-of-view afforded by the satellite-borne imager allows an unprecedented determination of the dynamics of this region, which has not previously been possible with ground-based observations. The location of the emission in latitude and magnetic local time varies in response to changes in the orientation of the IMF; the cusp MLT and the IMF By component are especially well correlated, the emission being located in the pre- or post-noon sectors for By < 0 nT or By > 0 nT, respectively. Simultaneous ground-based observations of the ionospheric plasma drift are provided by the CUTLASS Finland HF coherent radar. For an interval of IMF By approx 0 nT, these convection flow measurements suggest the presence of a clockwise-rotating lobe cell contained within the pre-noon dayside polar cap, with a flow reversal closely co-located with the high-latitude luminosity region. This pattern is largely consistent with recent theoretical predictions of the convection flow during northward IMF. We believe that this represents the first direct measurement of the convection flow at the imaged location of the footprint of the high-latitude reconnection site.

    Key words: Magnetospheric physics (auroral phenomena; magnetopause · cusp · and boundary layers; plasma convection

  2. Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

    Directory of Open Access Journals (Sweden)

    A. Grocott

    2006-12-01

    Full Text Available At 08:35 UT on 21 November 2004, the onset of an interval of substorm activity was captured in the southern hemisphere by the Far UltraViolet (FUV instrument on board the IMAGE spacecraft. This was accompanied by the onset of Pi2 activity and subsequent magnetic bays, evident in ground magnetic data from both hemispheres. Further intensifications were then observed in both the auroral and ground magnetic data over the following ~3 h. During this interval the fields-of-view of the two southern hemisphere Tasman International Geospace Enviroment Radars (TIGER moved through the evening sector towards midnight. Whilst initially low, the amount of backscatter from TIGER increased considerably during the early stages of the expansion phase such that by ~09:20 UT an enhanced dusk flow cell was clearly evident. During the expansion phase the equatorward portion of this flow cell developed into a narrow high-speed flow channel, indicative of the auroral and sub-auroral flows identified in previous studies (e.g. Freeman et al., 1992; Parkinson et al., 2003. At the same time, higher latitude transient flow features were observed and as the interval progressed the flow reversal region and Harang discontinuity became very well defined. Overall, this study has enabled the spatial and temporal development of many different elements of the substorm process to be resolved and placed within a simple conceptual framework of magnetospheric convection. Specifically, the detailed observations of ionospheric flows have illustrated the complex interplay between substorm electric fields and associated auroral dynamics. They have helped define the distinct nature of different substorm current systems such as the traditional substorm current wedge and the more equatorward currents associated with polarisation electric fields. Additionally, they have revealed a radar signature of nightside reconnection which provides the promise of quantifying nightside reconnection in a

  3. The Protonics project: distributed observations of auroral dayside Doppler-shifted hydrogen emissions

    OpenAIRE

    Holmes, Jeffrey Morgan

    2014-01-01

    The Protonics project is an effort to further understand the spatio-temporal dynamics of dayside auroral hydrogen emissions, also known as dayside proton aurorae. Spectrometers measuring dayside Balmer α (Hα) and Balmer β (Hβ) were deployed to two locations on Svalbard at Longyearbyen and Ny-Ålesund. Measured hydrogen Doppler profiles were analysed via a Monte Carlo model of proton precipitation, resulting in an estimate of characteristic energy of the precipitating proton/hydrogen population...

  4. Nonlinear wave structures in collisional plasma of auroral E-region ionosphere

    Directory of Open Access Journals (Sweden)

    A. V. Volosevich

    Full Text Available Studies of the auroral plasma with small-scale inhomogenieties producing the VHF-radar reflections (radar aurora when observed in conditions of the saturated Farley-Buneman instability within the auroral E region, show strong nonlinear interactions and density fluctuations of 5–15%. Such nonlinearity and high fluctation amplitudes are inconsistent with the limitations of the weak turbulence theory, and thus a theory for arbitrary amplitudes is needed. To this end, a nonlinear theory is described for electrostatic MHD moving plasma structures of arbitrary amplitude for conditions throughout the altitude range of the collisional auroral E region. The equations are derived, from electron and ion motion self-consistent with the electric field, for the general case of the one-dimensional problem. They take into account nonlinearity, electron and ion inertia, diffusion, deviation from quasi-neutrality, and dynamical ion viscosity. The importance of the ion viscosity for dispersion is stressed, while deviation from the quasi-neutrality can be important only at rather low plasma densities, not typical for the auroral E region. In a small amplitude limit these equations have classical nonlinear solutions of the type of "electrostatic shock wave" or of knoidal waves. In a particular case these knoidal waves degrade to a dissipative soliton. A two-dimensional case of a quasi-neutral plasma is considered in the plane perpendicular to the magnetic field by way of the Poisson brackets, but neglecting the nonlinearity and ion inertia. It is shown that in these conditions an effective saturation can be achieved at the stationary turbulence level of order of 10%.

  5. Study of AKR hollow pattern characteristics at sub-auroral regions

    Science.gov (United States)

    Boudjada, Mohammed Y.; Sawas, Sami; Galopeau, Patrick; Berthelier, Jean-Jacques; Schwingenschuh, Konrad

    2014-05-01

    The Earth's auroral kilometric radiation (AKR) is expected to exhibit a hollow pattern similar to that reported for the comparable emissions from Jupiter (e.g. Jovian decametric emissions - DAM). The hollow pattern is a hollow cone beam with apex at the point of AKR emission, axis tangent to the magnetic field direction, and an opening angle of the order of 80°. The properties of the hollow cone can be derived from the so-called dynamic spectrum which displays the radiation versus the observation time and the frequency. We analyze the auroral kilometric radiation recorded by the electric field experiment (ICE) onboard DEMETER micro-satellite. The dynamic spectra lead us to study the occurrence of the AKR recorded in the sub-auroral regions when the micro-satellite was at altitudes of about 700 km. We address in this contribution issues concerning the characteristics (occurrence, latitude and longitude) of the AKR hollow beam and their relations to the seasonal and solar activity variations.

  6. Using spectral characteristics to interpret auroral imaging in the 731.9 nm O+ line

    Directory of Open Access Journals (Sweden)

    A. Strømme

    2008-07-01

    Full Text Available Simultaneous observations were made of dynamic aurora during substorm activity on 26 January 2006 with three high spatial and temporal resolution instruments: the ASK (Auroral Structure and Kinetics instrument, SIF (Spectrographic Imaging Facility and ESR (EISCAT Svalbard Radar, all located on Svalbard (78° N, 16.2° E. One of the narrow field of view ASK cameras is designed to detect O+ ion emission at 731.9 nm. From the spectrographic data we have been able to determine the amount of contaminating N2 and OH emission detected in the same filter. This is of great importance to further studies using the ASK instrument, when the O+ ion emission will be used to detect flows and afterglows in active aurora. The ratio of O+ to N2 emission is dependent on the energy spectra of electron precipitation, and was found to be related to changes in the morphology of the small-scale aurora. The ESR measured height profiles of electron densities, which allowed estimates to be made of the energy spectrum of the precipitation during the events studied with optical data from ASK and SIF. It was found that the higher energy precipitation corresponded to discrete and dynamic features, including curls, and low energy precipitation corresponded to auroral signatures that were dominated by rays. The evolution of these changes on time scales of seconds is of importance to theories of auroral acceleration mechanisms.

  7. Electron distribution function behavior during localized transverse ion acceleration events in the topside auroral zone

    Energy Technology Data Exchange (ETDEWEB)

    Lynch, K.A.; Arnoldy, R.L. [Univ. of New Hampshire, Durham, NH (United States); Kintner, P.M. [Cornell Univ., Ithaca, NY (United States); Vago, J.L. [European Space Agency, Noordwijk (Netherlands)

    1994-02-01

    The Topaz3 auroral sounding rocket made the following observations concerning the transfer of precipitating auroral electron energy to transverse ion acceleration in the topside auroral zone. During the course of the flight, the precipitating electron beam was modified to varying degrees by interaction with VLF hiss, at times changing the beam into a field-aligned plateau. The electron distribution functions throughout the flight are classified according to the extent of this modification, and correspondences with ion acceleration events are sought. The hiss power during most of this rocket flight apparently exceeded the threshold for collapse into solitary structures. At the times of plateaued electron distributions, the collapse of these structures was limited by Landau damping through the ambient ions, resulting in a velocity-dependent acceleration of both protons and oxygen. This initial acceleration is sufficient to supply the number flux of upflowing ions observed at satellite altitudes. The bursty ion acceleration was anticorrelated, on 1-s or smaller timescales, with dispersive bursts of precipitating field-aligned electrons, although on longer timescales the bursty ions and the bursty electrons are correlated. 45 refs., 9 figs.

  8. Anomalous width variation of rarefactive ion acoustic solitary waves in the context of auroral plasmas

    Directory of Open Access Journals (Sweden)

    S. S. Ghosh

    2004-01-01

    Full Text Available The presence of dynamic, large amplitude solitary waves in the auroral regions of space is well known. Since their velocities are of the order of the ion acoustic speed, they may well be considered as being generated from the nonlinear evolution of ion acoustic waves. However, they do not show the expected width-amplitude correlation for K-dV solitons. Recent POLAR observations have actually revealed that the low altitude rarefactive ion acoustic solitary waves are associated with an increase in the width with increasing amplitude. This indicates that a weakly nonlinear theory is not appropriate to describe the solitary structures in the auroral regions. In the present work, a fully nonlinear analysis based on Sagdeev pseudopotential technique has been adopted for both parallel and oblique propagation of rarefactive solitary waves in a two electron temperature multi-ion plasma. The large amplitude solutions have consistently shown an increase in the width with increasing amplitude. The width-amplitude variation profile of obliquely propagating rarefactive solitary waves in a magnetized plasma have been compared with the recent POLAR observations. The width-amplitude variation pattern is found to fit well with the analytical results. It indicates that a fully nonlinear theory of ion acoustic solitary waves may well explain the observed anomalous width variations of large amplitude structures in the auroral region.

  9. ;Long-hissler; fine structure within auroral hiss: A review and synthesis

    Science.gov (United States)

    Kim, Howard F.; LaBelle, James; Spasojević, Maria

    2017-04-01

    One of the most prominent fine-structures of auroral hiss is the ;long-hissler;, defined here as a dispersed feature embedded within broadband auroral hiss emissions in the frequency range 1-40 kHz and lasting longer than 0.3 s. While theory is limited, there is evidence that hisslers can be used in remote sensing of density characteristics at altitudes of thousands of km. By applying an automatic threshold algorithm to VLF data collected at South Pole 2230-0130 UT daily during June-August 2014, 22 h of auroral hiss are identified on 49 of 93 days analyzed, for an occurrence rate of 9.7% during the applicable MLT interval. From manual inspection of these intervals, 414 groups (trains) of long hisslers are identified on 34 of the 49 days on which hiss occurred. Median lower (upper) frequency bounds of these features are 8 (22) kHz, median frequency-time slope is -10 kHz/s, and median hissler repetition time within a train (hissler period) is 1.2 s. Hissler period and frequency-time slope are inversely related. Data from previous studies are reviewed to provide a comprehensive description of the phenomenon. Contrary to some previous studies, subsequent long hissler features are found to commonly overlap in time, and no evidence is found for an inverse relationship between hissler train duration and geomagnetic activity.

  10. Coordinated ground and space measurements of auroral surge over South Pole. Technical report

    Energy Technology Data Exchange (ETDEWEB)

    Rosenberg, T.J.; Detrick, D.L.; Mizera, P.F.; Gorney, D.J.; Berkey, F.T.

    1988-02-01

    Coincident ground-based and satellite observations are presented of a premidnight auroral surge over Amundsen-Scott South Pole station. The set of near-simultaneous measurements provides an excellent opportunity to gain a more-quantitative understanding of the nature of premidnight substorm activity at high geomagnetic latitudes. The surge produced a rapid onset of cosmic radio noise absorption at the station. On the polar-orbiting DMSP-F6 spacecraft, intense x-ray emissions with E > 2-keV energy were imaged 1 to 2 deg magnetically equatorward of the South Pole approximately 1 min prior to the peak of the absorption event. The precipitating electron spectrum determined from the x-ray measurements could be characterized by an e-folding energy of approx. 11 keV and is found to be adequate to account for the cosmic noise absorption and maximum auroral luminosity recorded at South Pole. Photometer, all-sky camera, riometer, and magnetometer data are used to estimate the velocity of motion and spatial extent of the auroral precipitation and the ionospheric currents associated with the surge.

  11. Observations of meso-scale neutral wind interaction with auroral precipitation in the thermosphere at EISCAT

    Science.gov (United States)

    Kosch, Michael; Nozawa, Satonori; Yiu, Ho-Ching Iris; Anderson, Callum; Ogawa, Yasunobu; Howells, Vikki; Baddeley, Lisa; Aruliah, Anasuya; McWhirter, Ian; McCrea, I. W.; Fujii, Ryoichi

    We report on observations of E-region neutral wind fields and their interaction with auroral precipitation at meso-scale spatial resolution. The EISCAT Svalbard radar was used to observe the ionospheric line-of-sight ion flows and temperatures in the E-and F-regions whilst scan-ning its beam. An all-sky optical Scanning Doppler Imager was used at 557.7 nm to observe thermospheric neutral line-of-sight winds and temperatures. High-latitude data from February 2010 are presented. In the case of an auroral arc, strong acceleration of the E-region neutral wind occurs within 10s of km to the arc on a time scale of 10s of minutes. We demonstrate through modelling that this effect cannot be explained by height changes in the 557.7 nm emis-sion layer. The most likely explanation seems to be greatly enhanced ion drag associated with the increased plasma density caused by the particle precipitation, and the localised ionospheric electric field associated with the Pedersen closure current of auroral arcs. Since Joule heat-ing occurs predominantly in the E-region, meso-scale variability in the thermosphere probably accounts for a significant under-estimation in the total energy dissipation.

  12. Average and worst-case specifications of precipitating auroral electron environment

    Science.gov (United States)

    Hardy, D. A.; Burke, W. J.; Gussenhoven, M. S.; Holeman, E.; Yeh, H. C.

    1985-01-01

    The precipitation electrons in the auroral environment are highly variable in their energy and intensity in both space and time. As such they are a source of potential hazard to the operation of the Space Shuttle and other large spacecraft operating in polar orbit. In order to assess these hazards both the average and extreme states of the precipitating electrons must be determined. Work aimed at such a specification is presented. First results of a global study of the average characteristics are presented. In this study the high latitude region was divided into spatial elements in magnetic local time and corrected geomagnetic latitude. The average electron spectrum was then determined in each spatial element for seven different levels of activity as measured by K sub p using an extremely large data set of auroral observations. Second a case study of an extreme auroral electron environment is presented, in which the electrons are accelerated through field aligned potential as high as 30,000 volts and in which the spacecraft is seen to charge negatively to a potential approaching .5 kilovolts.

  13. GREECE -- Ground-to-Rocket Electrodynamics-Electrons Correlative Experiment: High resolution rocket and ground-based investigations of small-scale auroral structure and dynamics Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Methodology The methodology is based on making comparisons between downward electron flux, DC electric fields, electromagnetic waves, and auroral morphology. The...

  14. Correlated variations of UV and radio emissions during an outstanding Jovian auroral event

    Science.gov (United States)

    Prange, R.; Zarka, P.; Ballester, G. E.; Livengood, T. A.; Denis, L.; Carr, T.; Reyes, F.; Bame, S. J.; Moos, H. W.

    1993-01-01

    An exceptional Jovian aurora was detected in the FUV on December 21, 1990, by means of Vilspa and Goddard Space Flight Center (GFSC) International Ultraviolet Explorer (IUE) observations. This event included intensification by a factor of three between December 20 and 21, leading to the brightest aurora identified in the IUE data analyzed, and, in the north, to a shift of the emission peak towards larger longitudes. The Jovian radio emission simultaneously recorded at decameter wavelengths in Nancay also exhibits significant changes, from a weak and short-duration emission on December 20 to a very intense one, lasting several hours, on December 21. Confirmation of this intense radio event is also found in the observations at the University of Florida on December 21. The emissions are identified as right-handed Io-independent 'A' (or 'non Io-A') components from the northern hemisphere. The radio source region deduced from the Nancay observations lies, for both days, close to the UV peak emission, exhibiting in particular a similar shift of the source region toward larger longitudes from one day to the next. A significant broadening of the radio source was also observed and it is shown that on both days, the extent of the radio source closely followed the longitude range for which the UV brightness exceeds a given threshold. The correlated variations, both in intensity and longitude, strongly suggest that a common cause triggered the variation of the UV and radio emissions during this exceptional event. On one hand, the variation of the UV aurora could possibly be interpreted according to the Prange and Elkhamsi (1991) model of diffuse multicomponent auroral precipitation (electron and ion): it would arise from an increase in the precipitation rate of ions together with an inward shift of their precipitation locus from L approximately equal 10 to L approximately equal 6. On the other hand, the analysis of Ulysses observations in the upstream solar wind suggests that

  15. Localized Ionospheric Particle Acceleration and Wave Acceleration of Auroral Ions: Amicist Data Set

    Science.gov (United States)

    Lynch, Kristina A.

    1999-01-01

    Research supported by this grant covered two main topics: auroral ion acceleration from ELF-band wave activity, and from VLF-spikelet (lower hybrid solitary structure) wave activity. Recent auroral sounding rocket data illustrate the relative significance of various mechanisms for initiating auroral ion outflow. Two nightside mechanisms are shown in detail. The first mechanism is ion acceleration within lower hybrid solitary wave events. The new data from this two payload mission show clearly that: (1) these individual events are spatially localized to scales approximately 100 m wide perpendicular to B, in agreement with previous investigations of these structures, and (2) that the probability of occurrence of the events is greatest at times of maximum VLF wave intensity. The second mechanism is ion acceleration by broadband, low frequency electrostatic waves, observed in a 30 km wide region at the poleward edge of the arc. The ion fluxes from the two mechanisms are compared and it is shown that while lower hybrid solitary structures do indeed accelerate ions in regions of intense VLF waves, the outflow from the electrostatic ion wave acceleration region is dominant for the aurora investigated by this sounding rocket, AMICIST. The fluxes are shown to be consistent with DE-1 and Freja outflow measurements, indicating that the AMICIST observations show the low altitude, microphysical signatures of nightside auroral outflow. In this paper, we present a review of sounding rocket observations of the ion acceleration seen nightside auroral zone lower hybrid solitary structures. Observations from Topaz3, Amicist, and Phaze2 are presented on various spatial scales, including the two-point measurements of the Amicist mission. From this collection of observations, we will demonstrate the following characteristics of transverse ion acceleration (TAI) in LHSS. The ion acceleration process is narrowly confined to 90 degrees pitch angle, in spatially confined regions of up to a

  16. Locating the Polar Cap Boundary of Postnoon Sector from Observations of 630.0 nm Auroral Emission at Zhongshan Station

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    We studied the ground observations of 630. 0 nm auroral emission at Zhongshan Station to de-termine the polar cap boundary with the latitudinal profile of emission intensity. The open-closed field lineboundary is assumed to lie at the boundary between polar rain and plasma sheet precipitation. We assumethat nonprecipitation-dependent sources of 630. 0 nm emission cause a spatially uniform luminosity in thepolar cap and that auroral zone luminosity is also spatially uniform. Therefore we determine the locationof the polar cap boundary of postnoon sector from the auroral emission data each time by finding the bestfit of the observations to a step function in latitude and we produce a time series of the location of the polarcap boundary. The average error of the practice in the paper is less than 0. 8 degree.

  17. A Wide Field Auroral Imager (WFAI for low Earth orbit missions

    Directory of Open Access Journals (Sweden)

    N. P. Bannister

    2007-03-01

    Full Text Available A comprehensive understanding of the solar wind interaction with Earth's coupled magnetosphere-ionosphere system requires an ability to observe the charged particle environment and auroral activity from the same platform, generating particle and photon image data which are matched in time and location. While unambiguous identification of the particles giving rise to the aurora requires a Low Earth Orbit satellite, obtaining adequate spatial coverage of aurorae with the relatively limited field of view of current space bourne auroral imaging systems requires much higher orbits. A goal for future satellite missions, therefore, is the development of compact, wide field-of-view optics permitting high spatial and temporal resolution ultraviolet imaging of the aurora from small spacecraft in low polar orbit. Microchannel plate optics offer a method of achieving the required performance. We describe a new, compact instrument design which can observe a wide field-of-view with the required spatial resolution. We report the focusing of 121.6 nm radiation using a spherically-slumped, square-pore microchannel plate with a focal length of 32 mm and an F number of 0.7. Measurements are compared with detailed ray-trace simulations of imaging performance. The angular resolution is 2.7±0.2° for the prototype, corresponding to a footprint ~33 km in diameter for an aurora altitude of 110 km and a spacecraft altitude of 800 km. In preliminary analysis, a more recent optic has demonstrated a full width at half maximum of 5.0±0.3 arcminutes, corresponding to a footprint of ~1 km from the same spacecraft altitude. We further report the imaging properties of a convex microchannel plate detector with planar resistive anode readout; this detector, whose active surface has a radius of curvature of only 100 mm, is shown to meet the spatial resolution and sensitivity requirements of the new wide field auroral imager (WFAI.

  18. Jupiter's auroral-related thermal infrared emission from IRTF-TEXES

    Science.gov (United States)

    Sinclair, James; Orton, Glenn; Greathouse, Thomas; Fletcher, Leigh; Irwin, Patrick

    2015-11-01

    Auroral processes on Jupiter can be observed at a large range of wavelengths. Charged particles of the solar wind are deflected by Jupiter’s magnetic field and penetrate the atmosphere at high latitudes. This results in ion and/or electron precipitation, which produces emission at X-ray, UV, visible, near-infrared and even radio wavelengths. These observations indicate three distinct features of the aurora: 1) filament-like oval structures fixed at the magnetic poles (~80°W (System III) in the south, ~180°W in the north), 2) spatially-continuous but transient aurora that fill these oval regions and 3) discrete spots associated with the magnetic footprints of Io and other Galilean satellites. However, observations in the thermal infrared indicate the aurora also modify the neutral atmosphere. Enhanced emission of CH4 is observed coincident with the auroral ovals and indicates heightened stratospheric temperatures possibly as a result of joule heating by the influx of charged particles. Stronger emission is also observed of C2H2, C2H4, C2H6 and even C6H6 though previous work has struggled to determine whether this is a temperature or compositional effect. In order to quantify the auroral effects on the neutral atmosphere and to support the 2016 Juno mission (which has no thermal infrared instrument) we have performed a retrieval analysis of IRTF-TEXES (Texas Echelon Cross Echelle Spectrograph, 5- to 25-μm) spectra obtained on Dec 11th 2014 near solar maximum. The instrument slit was scanned east-west across high latitudes in each hemisphere and Jupiter’s rotation was used to obtain ~360° longitudinal coverage. Spectra of H2 S(1), CH4, C2H2, C2H4 and C2H6 emission were measured at a resolving power of R = 85000, allowing a large vertical range in the atmosphere (100 - 0.001 mbar) to be sounded. Preliminary retrievals of the vertical temperature profile from H2 S(1) and CH4 measurements at 60°N, 180°W (on aurora), in comparison to 60°N, 60°W (quiescent

  19. Ionospheric Plasma Circulation Associated with Polar Cap Arcs Detached from the Auroral Oval

    Science.gov (United States)

    Yakymenko, K.; Koustov, A. V.; Hosokawa, K.; Shiokawa, K.

    2015-12-01

    Joint observations of the OMTI all-sky camera at Resolute Bay, NWT (Canada), the SuperDARN radars and Swarm satellites are considered to investigate horizontal plasma flows and vertical field-aligned currents (FACs) associated with polar cap arcs "detached" from the auroral oval but not penetrated deep into the polar cap. All cases are for the near winter solstice, positive IMF Bz and mostly dominating IMF By. We show that the arcs are usually co-exist with strong flow shears driven by electric fields of the converging type. The shears, being added to the background flow, produce unusual convection patterns, for example reverse (sunward) flows on the nightside, several MLT hours away from the noon-midnight line. We also investigate the distribution of FACs in the arcs' vicinity, both duskward and dawnward, for several Swarm passes. Electron density data onboard Swarm satellites are used to identify the arc and auroral oval boundaries, along with the ground-based optics. The data suggest that the arcs correspond to a separate current system excited in addition to the background plasma circulation governed by the reconnection processes.Joint observations of the OMTI all-sky camera at Resolute Bay, NWT (Canada), the SuperDARN radars and Swarm satellites are considered to investigate horizontal plasma flows and vertical field-aligned currents (FACs) associated with polar cap arcs "detached" from the auroral oval but not penetrated deep into the polar cap. All cases are for the near winter solstice, positive IMF Bz and mostly dominating IMF By. We show that the arcs are usually co-exist with strong flow shears driven by electric fields of the converging type. The shears, being added to the background flow, produce unusual convection patterns, for example reverse (sunward) flows on the nightside, several MLT hours away from the noon-midnight line. We also investigate the distribution of FACs in the arcs' vicinity, both duskward and dawnward, for several Swarm passes

  20. Observations of E region irregularities generated at auroral latitudes by a high-power radio wave

    Science.gov (United States)

    Djuth, F. T.; Jost, R. J.; Noble, S. T.; Gordon, W. E.; Stubbe, P.

    1985-01-01

    The initial results of a series of observations made with the high-power HF heating facility near Tromso, Norway are reported. During these experiments, attention was focused on the production of artificial geomagnetic field-aligned irregularities (AFAIs) in the auroral E region by HF waves. A mobile 46.9-MHz radar was used to diagnose the formation of AFAIs having spatial scales of 3.2 across geomagnetic field lines. The dynamic characteristics of the AFAIs are discussed within the context of current theoretical work dealing with the natural production of AFAIs in the ionosphere.

  1. Auroral vortex street formed by the magnetosphere-ionosphere coupling instability

    CERN Document Server

    Hiraki, Yasutaka

    2014-01-01

    By performing three-dimensional nonlinear MHD simulations including Alfven eigenmode perturbations most unstable to the ionospheric feedback effects, we reproduced the auroral vortex street that often appears just before substorm onset. We found that an initially placed arc splits, intensifies, and rapidly deforms into a vortex street. We also found that there is a critical convection electric field for growth of the Alfven eigenmodes. The vortex street is shown to be a consequence of coupling between the magnetospheric Alfven waves carrying field-aligned currents and the ionospheric density waves driven by Pedersen/Hall currents.

  2. Studies of the auroral ionosphere with the MITHRAS. Final report, October 1982-October 1985

    Energy Technology Data Exchange (ETDEWEB)

    Foster, J.C.

    1986-06-26

    The extensive MITHRAS radar data set was the object of extensive analyses the processes and characteristics of the auroral-latitude ionosphere and thermosphere: 1) High-Latitude Electrodynamics: Ionospheric response to substorms at widely separated local times was investigated. 2) Ionospheric Plasma Transport: The effects of plasma convection on the formation of the midlatitude trough were studied utilizing the wide spatial field of view of the Millstone radar. 3) Convection Snapshots: Simultaneous data from spaced instruments were combined to produce 'snapshots' of the polar and auroral convection pattern. 4) Comparisons with Models: 5) Data Bases Studies and Empirical Models: The extensive data set which resulted from the MITHRAS experimental program was incorporated into a multi-instrument, common format data base. 6) Azimuth Scan Experiments: Analysis of the complex data during MITHRAS azimuth scanning experiments resulted in the capability of mapping the convection electric field within the extended field of the radar. 7) Thermosphere and Exosphere: The diurnal variation of exospheric temperature over 30 degrees of latitude around Millstone Hill was investigated using MITHRAS elevation scan data.

  3. In-situ observation of electron kappa distributions associated with discrete auroral arcs

    Science.gov (United States)

    Ogasawara, Keiichi; Livadiotis, George; Samara, Marilia; Michell, Robert; Grubbs, Guy

    2016-04-01

    The Medium-energy Electron SPectrometer (MESP) sensor aboard a NASA sounding rocket was launched from Poker Flat Research Range on 3 March 2014 as a part of Ground-to-Rocket Electrodynamics-Electrons Correlative Experiment (GREECE) mission. GREECE targeted to discover convergent E-field structures at low altitude ionosphere to find their contribution to the rapid fluid-like structures of aurora, and MESP successfully measured the precipitating electrons from 2 to 200 keV within multiple discrete auroral arcs with the apogee of 350 km. MESP's unprecedented electron energy acceptance and high geometric factor made it possible to investigate precise populations of the suprathermal components measured in the inverted-V type electron energy distributions. The feature of these suprathermal electrons are explained by the kappa distribution functions with the parameters (densty, temperature, and kappa) consistent with the near-Earth tail plasma sheet, suggesting the source population of the auroral electrons. The kappa-values are different between each arc observed as a function of latitude, but are almost stable within one discrete arc. We suggest that this transition of kappa reflects the probagation history of source electrons through the plasma sheet by changing its state from non-equilibrium electron distributions to thermal ones.

  4. Development and performance of a suprathermal electron spectrometer to study auroral precipitations

    Science.gov (United States)

    Ogasawara, Keiichi; Grubbs, Guy; Michell, Robert G.; Samara, Marilia; Stange, Jason L.; Trevino, John A.; Webster, James; Jahn, Jörg-Micha

    2016-05-01

    The design, development, and performance of Medium-energy Electron SPectrometer (MESP), dedicated to the in situ observation of suprathermal electrons in the auroral ionosphere, are summarized in this paper. MESP employs a permanent magnet filter with a light tight structure to select electrons with proper energies guided to the detectors. A combination of two avalanche photodiodes and a large area solid-state detector (SSD) provided 46 total energy bins (1 keV resolution for 3-20 keV range for APDs, and 7 keV resolution for >20 keV range for SSDs). Multi-channel ultra-low power application-specific integrated circuits are also verified for the flight operation to read-out and analyze the detector signals. MESP was launched from Poker Flat Research Range on 3 March 2014 as a part of ground-to-rocket electrodynamics-electrons correlative experiment (GREECE) mission. MESP successfully measured the precipitating electrons from 3 to 120 keV in 120-ms time resolution and characterized the features of suprathermal distributions associated with auroral arcs throughout the flight. The measured electrons were showing the inverted-V type spectra, consistent with the past measurements. In addition, investigations of the suprathermal electron population indicated the existence of the energetic non-thermal distribution corresponding to the brightest aurora.

  5. Alaskan Auroral All-Sky Images on the World Wide Web

    Science.gov (United States)

    Stenbaek-Nielsen, H. C.

    1997-01-01

    In response to a 1995 NASA SPDS announcement of support for preservation and distribution of important data sets online, the Geophysical Institute, University of Alaska Fairbanks, Alaska, proposed to provide World Wide Web access to the Poker Flat Auroral All-sky Camera images in real time. The Poker auroral all-sky camera is located in the Davis Science Operation Center at Poker Flat Rocket Range about 30 miles north-east of Fairbanks, Alaska, and is connected, through a microwave link, with the Geophysical Institute where we maintain the data base linked to the Web. To protect the low light-level all-sky TV camera from damage due to excessive light, we only operate during the winter season when the moon is down. The camera and data acquisition is now fully computer controlled. Digital images are transmitted each minute to the Web linked data base where the data are available in a number of different presentations: (1) Individual JPEG compressed images (1 minute resolution); (2) Time lapse MPEG movie of the stored images; and (3) A meridional plot of the entire night activity.

  6. EISCAT observations of plasma patches at sub-auroral cusp latitudes

    Directory of Open Access Journals (Sweden)

    J. Moen

    2006-09-01

    Full Text Available A sequence of 3 patches of high-density (1012 m−3 cold plasma on a horizontal scale-size of 300–700 km was observed near magnetic noon by the EISCAT VHF radar above Svalbard on 17 December 2001. The patches followed a trajectory towards the cusp inflow region. The combination of radar and all-sky observations demonstrates that the patches must have been segmented equatorward of the cusp/cleft auroral display, and hence their properties had not yet been influenced by cusp particle showers and electrodynamics on open flux tubes. The last patch in the sequence was intersected by radio tomography observations, and was found to be located adjacent to a broader region of the same high electron density further south. The patches occurred under moderately active conditions (Kp=3 and the total electron content (TEC of the high-density plasma was 45 TEC units. The train of patches appeared as a segmentation of the tongue of ionization. The sequence of patches occurred in association with a sequence of flow bursts in the dusk cell return flow. It is proposed that reconnection driven pulsed convection is able to create sub-auroral patches in the region where high density mid-latitude plasma is diverted poleward toward the cusp. It is the downward Birkeland current sheet located at the equatorward boundary of the flow disturbance that represents the actual cutting mechanism.

  7. Zakharov simulations of beam-induced turbulence in the auroral ionosphere

    Science.gov (United States)

    Akbari, H.; Guio, P.; Hirsch, M. A.; Semeter, J. L.

    2016-05-01

    Recent detections of strong incoherent scatter radar echoes from the auroral F region, which have been explained as the signature of naturally produced Langmuir turbulence, have motivated us to revisit the topic of beam-generated Langmuir turbulence via simulation. Results from one-dimensional Zakharov simulations are used to study the interaction of ionospheric electron beams with the background plasma at the F region peak. A broad range of beam parameters extending by more than 2 orders of magnitude in average energy and electron number density is considered. A range of wave interaction processes, from a single parametric decay, to a cascade of parametric decays, to formation of stationary density cavities in the condensate region, and to direct collapse at the initial stages of turbulence, is observed as we increase the input energy to the system. The effect of suprathermal electrons, produced by collisional interactions of auroral electrons with the neutral atmosphere, on the dynamics of Langmuir turbulence is also investigated. It is seen that the enhanced Landau damping introduced by the suprathermal electrons significantly weakens the turbulence and truncates the cascade of parametric decays.

  8. An Ad-hoc Satellite Network to Measure Filamentary Current Structures in the Auroral Zone

    Science.gov (United States)

    Nabong, C.; Fritz, T. A.; Semeter, J. L.

    2014-12-01

    An ad-hoc cubesat-based satellite network project known as ANDESITE is under development at Boston University. It aims to develop a dense constellation of easy-to-use, rapidly-deployable low-cost wireless sensor nodes in space. The objectives of the project are threefold: 1) Demonstrate viability of satellite based sensor networks by deploying an 8-node miniature sensor network to study the filamentation of the field aligned currents in the auroral zones of the Earth's magnetosphere. 2) Test the scalability of proposed protocols, including localization techniques, tracking, data aggregation, and routing, for a 3 dimensional wireless sensor network using a "flock" of nodes. 3) Construct a 6U Cube-sat running the Android OS as an integrated constellation manager, data mule and sensor node deplorer. This small network of sensor nodes will resolve current densities at different spatial resolutions in the near-Earth magnetosphere using measurements from magnetometers with 1-nT sensitivities and 0.2 nT/√Hz self-noise. Mapping of these currents will provide new constraints for models of auroral particle acceleration, wave-particle interactions, ionospheric destabilization, and other kinetic processes operating in the low-beta plasma of the near Earth magnetosphere.

  9. Explaining Signatures of Auroral Arcs based on the Stationary Inertial Alfven Wave

    Science.gov (United States)

    Nogami, Sh; Koepke, Me; Knudsen, Dj; Gillies, Dm; Donovan, E.; Vincena, S.

    2016-10-01

    Optical emission data from the THEMIS array of All Sky Imagers are analyzed to determine the lifetime of an auroral arc (i.e., the elapsed time during which an arc is visible). Lifetime is an important temporal signature related to the arc generation mechanism, by which arcs can be distinguished. An arc with a lifetime greater than ten minutes is consistent with arc generation by Stationary Inertial Alfven Wave (StIAW) which supports a steady-state wave electric field component parallel to a background magnetic field. An StIAW is a non-fluctuating, non-travelling, spatially periodic pattern of perturbed ion density that is static in the laboratory frame. StIAWs are the predicted result of the interaction between a magnetic-field-aligned electron current and plasma convection perpendicular to a background magnetic field. Electrostatic probes measure the fixed pattern of perturbed ion density in LAPD-U. Electron acceleration due to StIAWs is being investigated as a mechanism for the formation and support of long-lived auroral arcs. Preliminary evidence of electron acceleration from laboratory experiment is reported. This work was supported by NSF Grant PHY-130-1896, Grants from the Canadian Space Agency, and the THEMIS ASI teams at UCalgary and UC Berkeley. Facility use and experimental assistance from BaPSF is gratefully acknowledged.

  10. The far-ultraviolet main auroral emission at Jupiter. Pt. 2. Vertical emission profile

    Energy Technology Data Exchange (ETDEWEB)

    Bonfond, B.; Gustin, J.; Gerard, J.C.; Grodent, D.; Radioti, A. [Liege Univ. (Belgium). Lab. de Physique Atmospherique et Planetaire; Palmaerts, B. [Liege Univ. (Belgium). Lab. de Physique Atmospherique et Planetaire; Max-Planck-Institut fuer Sonnensystemforschung, Goettingen (Germany); Badman, S.V. [Lancaster Univ. (United Kingdom). Dept. of Physics; Khurana, K.K. [California Univ., Los Angeles, CA (United States); Tao, C. [Institut de Recherche en Astrophysique et Planetologie, Toulouse (France)

    2015-07-01

    The aurorae at Jupiter are made up of many different features associated with a variety of generation mechanisms. The main auroral emission, also known as the main oval, is the most prominent of them as it accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range. The energy of the precipitating electrons is a crucial parameter to characterize the processes at play which give rise to these auroral emissions, and the altitude of the emissions directly depends on this energy. Here we make use of far-UV (FUV) images acquired with the Advanced Camera for Surveys on board the Hubble Space Telescope and spectra acquired with the Space Telescope Imaging Spectrograph to measure the vertical profile of the main emissions. The altitude of the brightness peak as seen above the limb is ∝ 400 km, which is significantly higher than the 250 km measured in the post-dusk sector by Galileo in the visible domain. However, a detailed analysis of the effect of hydrocarbon absorption, including both simulations and FUV spectral observations, indicates that FUV apparent vertical profiles should be considered with caution, as these observations are not incompatible with an emission peak located at 250 km. The analysis also calls for spectral observations to be carried out with an optimized geometry in order to remove observational ambiguities.

  11. X-Ray Probes of Jupiter's Auroral Zones, Galilean Moons, and the Io Plasma Torus

    Science.gov (United States)

    Elsner, R. F.; Ramsey, B. D.; Swartz, D. A.; Rehak, P.; Waite, J. H., Jr.; Cooper, J. F.; Johnson, R. E.

    2005-01-01

    Remote observations from the Earth orbiting Chandra X-ray Observatory and the XMM-Newton Observatory have shown the the Jovian system is a rich and complex source of x-ray emission. The planet's auroral zones and its disk are powerful sources of x-ray emission, though with different origins. Chandra observations discovered x-ray emission from the Io plasma torus and from the Galilean moons Io, Europa, and possibly Ganymede. The emission from the moons is due to bombardment of their surfaces by highly energetic magnetospheric protons, and oxygen and sulfur ions, producing fluorescent x-ray emission lines from the elements in their surfaces against an intense background continuum. Although very faint when observed from Earth orbit, an imaging x-ray spectrometer in orbit around the icy Galilean moons would provide a detail mapping of the elemental composition in their surfaces. Here we review the results of Chandra and XMM-Newton observations of the Jovian system and describe the characteristics of X-MIME, an imaging x-ray spectrometer undergoing study for possible application to future missions to Jupiter such as JIMO. X-MIME has the ultimate goal of providing detailed high-resolution maps of the elemental abundances of the surfaces of Jupiter's icy moons and Io, as well as detailed study of the x-ray mission from the Io plasma torus, Jupiter's auroral zones, and the planetary disk.

  12. Combined ESR and EISCAT observations of the dayside polar cap and auroral oval during the May 15, 1997 storm

    Directory of Open Access Journals (Sweden)

    H. Liu

    Full Text Available The high-latitude ionospheric response to a major magnetic storm on May 15, 1997 is studied and different responses in the polar cap and the auroral oval are highlighted. Depletion of the F2 region electron density occurred in both the polar cap and the auroral zone, but due to different physical processes. The increased recombination rate of O+ ions caused by a strong electric field played a crucial role in the auroral zone. The transport effect, however, especially the strong upward ion flow was also of great importance in the dayside polar cap. During the main phase and the beginning of the recovery phase soft particle precipitation in the polar cap showed a clear relation to the dynamic pressure of the solar wind, with a maximum cross-correlation coefficient of 0.63 at a time lag of 5 min.

    Key words: Ionosphere (auroral ionosphere; polar ionosphere - Magnetospheric physics (storms and substorms

  13. Ion shell distributions as free energy source for plasma waves on auroral field lines mapping to plasma sheet boundary layer

    Directory of Open Access Journals (Sweden)

    A. Olsson

    2004-06-01

    Full Text Available Ion shell distributions are hollow spherical shells in velocity space that can be formed by many processes and occur in several regions of geospace. They are interesting because they have free energy that can, in principle, be transmitted to ions and electrons. Recently, a technique has been developed to estimate the original free energy available in shell distributions from in-situ data, where some of the energy has already been lost (or consumed. We report a systematic survey of three years of data from the Polar satellite. We present an estimate of the free energy available from ion shell distributions on auroral field lines sampled by the Polar satellite below 6 RE geocentric radius. At these altitudes the type of ion shells that we are especially interested in is most common on auroral field lines close to the polar cap (i.e. field lines mapping to the plasma sheet boundary layer, PSBL. Our analysis shows that ion shell distributions that have lost some of their free energy are commonly found not only in the PSBL, but also on auroral field lines mapping to the boundary plasma sheet (BPS, especially in the evening sector auroral field lines. We suggest that the PSBL ion shell distributions are formed during the so-called Velocity Dispersed Ion Signatures (VDIS events. Furthermore, we find that the partly consumed shells often occur in association with enhanced wave activity and middle-energy electron anisotropies. The maximum downward ion energy flux associated with a shell distribution is often 10mWm-2 and sometimes exceeds 40mWm-2 when mapped to the ionosphere and thus may be enough to power many auroral processes. Earlier simulation studies have shown that ion shell distributions can excite ion Bernstein waves which, in turn, energise electrons in the parallel direction. It is possible that ion shell distributions are the link between the X-line and the auroral wave activity and electron

  14. Electron ionization of metastable nitrogen and oxygen atoms in relation to the auroral emissions

    Science.gov (United States)

    Pandya, Siddharth; Joshipura, K. N.

    Atomic and molecular excited metastable states (EMS) are exotic systems due to their special properties like long radiative life-time, large size (average radius) and large polarizability along with relatively smaller first ionization energy compared to their respective ground states (GS). The present work includes our theoretical calculations on electron impact ionization of metastable atomic states N( (2) P), N( (2) D) of nitrogen and O( (1) S), O( (1) D) of oxygen. The targets of our present interest, are found to be present in our Earth's ionosphere and they play an important role in auroral emissions observed in Earth’s auroral regions [1] as also in the emissions observed from cometary coma [2, 3] and airglow emissions. In particular, atomic oxygen in EMS can radiate, the visible O( (1) D -> (3) P) doublet 6300 - 6364 Å red doublet, the O( (1) S -> (1) D) 5577 Å green line, and the ultraviolet O( (1) S -> (3) P) 2972 Å line. For metastable atomic nitrogen one observes the similar emissions, in different wavelengths, from (2) D and (2) P states. At the Earth's auroral altitudes, from where these emissions take place in the ionosphere, energetic electrons are also present. In particular, if the metastable N as well as O atoms are ionized by the impact of electrons then these species are no longer available for emissions. This is a possible loss mechanism, and hence it is necessary to analyze the importance of electron ionization of the EMS of atomic O and N, by calculating the relevant cross sections. In the present paper we investigate electron ionization of the said metastable species by calculating relevant total cross sections. Our quantum mechanical calculations are based on projected approximate ionization contribution in the total inelastic cross sections [4]. Detailed results and discussion along with the significance of these calculations will be presented during the COSPAR-2014. References [1] A.Bhardwaj, and G. R. Gladstone, Rev. Geophys., 38

  15. Thermal ion measurements on board Interball Auroral Probe by the Hyperboloid experiment

    Directory of Open Access Journals (Sweden)

    N. Dubouloz

    Full Text Available Hyperboloid is a multi-directional mass spectrometer measuring ion distribution functions in the auroral and polar magnetosphere of the Earth in the thermal and suprathermal energy range. The instrument encompasses two analyzers containing a total of 26 entrance windows, and viewing in two almost mutually perpendicular half-planes. The nominal angular resolution is defined by the field of view of individual windows ≈13° × 12.5°. Energy analysis is performed using spherical electrostatic analyzers providing differential measurements between 1 and 80 eV. An ion beam emitter (RON experiment and/or a potential bias applied to Hyperboloid entrance surface are used to counteract adverse effects of spacecraft potential and thus enable ion measurements down to very low energies. A magnetic analyzer focuses ions on one of four micro-channel plate (MCP detectors, depending on their mass/charge ratio. Normal modes of operation enable to measure H+, He+, O++, and O+ simultaneously. An automatic MCP gain control software is used to adapt the instrument to the great flux dynamics encountered between spacecraft perigee (700 km and apogee (20 000 km. Distribution functions in the main analyzer half-plane are obtained after a complete scan of windows and energies with temporal resolution between one and a few seconds. Three-dimensional (3D distributions are measured in one spacecraft spin period (120 s. The secondary analyzer has a much smaller geometrical factor, but offers partial access to the 3D dependence of the distributions with a few seconds temporal resolution. Preliminary results are presented. Simultaneous, local heating of both H+ and O+ ions resulting in conical distributions below 80 eV is observed up to 3 Earth's radii altitudes. The thermal ion signatures associated with large-scale nightside magnetospheric boundaries are investigated and a new ion outflow feature is

  16. Solitary waves observed in the auroral zone: the Cluster multi-spacecraft perspective

    Directory of Open Access Journals (Sweden)

    J. S. Pickett

    2004-01-01

    Full Text Available We report on recent measurements of solitary waves made by the Wideband Plasma Wave Receiver located on each of the four Cluster spacecraft at 4.5-6.5RE (well above the auroral acceleration region as they cross field lines that map to the auroral zones. These solitary waves are observed in the Wideband data as isolated bipolar and tripolar waveforms. Examples of the two types of pulses are provided. The time durations of the majority of both types of solitary waves observed in this region range from about 0.3 up to 5ms. Their peak-to-peak amplitudes range from about 0.05 up to 20mV/m, with a few reaching up to almost 70mV/m. There is essentially no potential change across the bipolar pulses. There appears to be a small, measurable potential change, up to 0.5V, across the tripolar pulses, which is consistent with weak or hybrid double layers. A limited cross-spacecraft correlation study was carried out in order to identify the same solitary wave on more than one spacecraft. We found no convincing correlations of the bipolar solitary waves. In the two cases of possible correlation of the tripolar pulses, we found that the solitary waves are propagating at several hundred to a few thousand km/s and that they are possibly evolving (growing, decaying as they propagate from one spacecraft to the next. Further, they have a perpendicular (to the magnetic field width of 50km or greater and a parallel width of about 2-5km. We conclude, in general, however, that the Cluster spacecraft at separations along and perpendicular to the local magnetic field direction of tens of km and greater are too large to obtain positive correlations in this region. Looking at the macroscale of the auroral zone at 4.5-6.5RE, we find that the onsets of the broadband electrostatic noise associated with the solitary waves observed in the spectrograms of the WBD data are generally consistent with propagation of the solitary waves up the field lines (away from Earth, or with

  17. Saturn's polar ionospheric flows and their relation to the main auroral oval

    Directory of Open Access Journals (Sweden)

    S. W. H. Cowley

    2004-04-01

    Full Text Available We consider the flows and currents in Saturn's polar ionosphere which are implied by a three-component picture of large-scale magnetospheric flow driven both by planetary rotation and the solar wind interaction. With increasing radial distance in the equatorial plane, these components consist of a region dominated by planetary rotation where planetary plasma sub-corotates on closed field lines, a surrounding region where planetary plasma is lost down the dusk tail by the stretching out of closed field lines followed by plasmoid formation and pinch-off, as first described for Jupiter by Vasyliunas, and an outer region driven by the interaction with the solar wind, specifically by reconnection at the dayside magnetopause and in the dawn tail, first discussed for Earth by Dungey. The sub-corotating flow on closed field lines in the dayside magnetosphere is constrained by Voyager plasma observations, showing that the plasma angular velocity falls to around half of rigid corotation in the outer magnetosphere, possibly increasing somewhat near the dayside magnetopause, while here we provide theoretical arguments which indicate that the flow should drop to considerably smaller values on open field lines in the polar cap. The implied ionospheric current system requires a four-ring pattern of field-aligned currents, with distributed downward currents on open field lines in the polar cap, a narrow ring of upward current near the boundary of open and closed field lines, and regions of distributed downward and upward current on closed field lines at lower latitudes associated with the transfer of angular momentum from the planetary atmosphere to the sub-corotating planetary magnetospheric plasma. Recent work has shown that the upward current associated with sub-corotation is not sufficiently intense to produce significant auroral acceleration and emission. Here we suggest that the observed auroral oval at Saturn instead corresponds to the ring of

  18. Statistical study of Saturn's auroral electron properties with Cassini/UVIS FUV spectral images

    Science.gov (United States)

    Gustin, J.; Grodent, D.; Radioti, A.; Pryor, W.; Lamy, L.; Ajello, J.

    2017-03-01

    About 2000 FUV spectra of different regions of Saturn's aurora, obtained with Cassini/UVIS from December 2007 to October 2014 have been examined. Two methods have been employed to determine the mean energy of the precipitating electrons. The first is based on the absorption of the auroral emission by hydrocarbons and the second uses the ratio between the brightness of the Lyman-α line and the H2 total UV emission (Lyα/H2), which is directly related to via a radiative transfer formalism. In addition, two atmospheric models obtained recently from UVIS polar occultations have been employed for the first time. It is found that the atmospheric model related to North observations near 70° latitude provides the results most consistent with constraints previously published. On a global point of view, the two methods provide comparable results, with mostly in the 7-17 keV range with the hydrocarbon method and in the 1-11 keV range with the Lyα/H2 method. Since hydrocarbons have been detected on ∼20% of the auroral spectra, the Lyα/H2 technique is more effective to describe the primary auroral electrons, as it is applicable to all spectra and allows an access to the lowest range of energies (≤5 keV), unreachable by the hydrocarbon method. The distribution of is found fully compatible with independent HST/ACS constraints (emission peak in the 840-1450 km range) and FUSE findings (emission peaking at pressure level ≤0.2 μbar). In addition, exhibits enhancements in the 3 LT-10 LT sector, consistent with SKR intensity measurements. An energy flux-electron energy diagram built from all the data points strongly suggests that acceleration by field-aligned potentials as described by Knight's theory is a main mechanism responsible for electron precipitation creating the aurora. Assuming a fixed electron temperature of 0.1 keV, a best-fit equatorial electron source population density of 3 × 103 m-3 is derived, which matches very well to the plasma properties observed with

  19. Arturo A. Roig: la filosofía latinoamericana como filosofía auroral

    Directory of Open Access Journals (Sweden)

    Silvana P. Vignale

    2010-01-01

    Full Text Available La filosofía latinoamericana es presentada por el filósofo argentino Arturo Roig como una filosofía de la mañana, en contrapunto con una filosofía vespertina que supone todo un futuro contenido en su pasado. Una apertura al futuro como alteridad desde una filosofía auroral afirma, en primer lugar, la historicidad de todo hombre, que no se juega en una toma de conciencia histórica por parte de los sujetos determinados, sino en la posibilidad de ¿un hacerse y un gestarse¿ del sujeto. La historicidad, de esta manera, es pensada desde la normatividad propia de la construcción de la sujetividad. Concebido como un sujeto plural y relativo y anclado en su contexto y en su tiempo, la historicidad lo constituye.

  20. Transverse ion acceleration by localized lower hybrid waves in the topside auroral ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Vago, J.L.

    1992-01-01

    Up to now, observations had been unable to show conclusively a one-to-one correspondence between perpendicular ion acceleration and a particular type of plasma wave within the O(+) source region below 2000 km. In this thesis, the author demonstrates that intense (100-300 mV/m) lower hybrid waves are responsible for transversely accelerating H(+) and O(+) ions to characteristic energies of up to 6 eV. This wave-particle interaction takes place in thin filamentary density cavities oriented along geomagnetic field lines. The measurements discussed were conducted in the nightside auroral zone at altitudes between 500 km and 1100 km. The results are consistent with theories of lower hybrid wave condensation and collapse.

  1. Transverse ion acceleration by localized lower hybrid waves in the topside auroral ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Vago, J.L.; Kintner, P.M.; Chesney, S.W.; Arnoldy, R.L.; Lynch, K.A.; Moore, T.E.; Pollock, C.J. (Cornell Univ., Ithaca, NY (United States) New Hampshire Univ., Durham (United States) NASA, Marshall Space Flight Center, Huntsville, AL (United States))

    1992-11-01

    Up to now, observations had been unable to show conclusively a one-to-one correspondence between perpendicular ion acceleration and a particular type of plasma wave within the O(+) source region below 2000 km. In this paper we demonstrate that intense (100-300 mV/m) lower hybrid waves are responsible for transversely accelerating H(+) and O(+) ions to characteristic energies of up to 6 eV. This wave-particle interaction takes place in thin filamentary density cavities oriented along geomagnetic field lines. The measurements we discuss were conducted in the nightside auroral zone at latitudes between 500 km and 1100 km. Our results are consistent with theories of lower hybrid wave condensation and collapse. 50 refs.

  2. Transverse ion acceleration by localized lower hybrid waves in the topside auroral ionosphere

    Science.gov (United States)

    Vago, J. L.; Kintner, P. M.; Chesney, S. W.; Arnoldy, R. L.; Lynch, K. A.; Moore, T. E.; Pollock, C. J.

    1992-01-01

    Up to now, observations had been unable to show conclusively a one-to-one correspondence between perpendicular ion acceleration and a particular type of plasma wave within the O(+) source region below 2000 km. In this paper we demonstrate that intense (100-300 mV/m) lower hybrid waves are responsible for transversely accelerating H(+) and O(+) ions to characteristic energies of up to 6 eV. This wave-particle interaction takes place in thin filamentary density cavities oriented along geomagnetic field lines. The measurements we discuss were conducted in the nightside auroral zone at latitudes between 500 km and 1100 km. Our results are consistent with theories of lower hybrid wave condensation and collapse.

  3. Stellar wind-magnetosphere interaction at exoplanets: computations of auroral radio powers

    CERN Document Server

    Nichols, J D

    2016-01-01

    We present calculations of the auroral radio powers expected from exoplanets with magnetospheres driven by an Earth-like magnetospheric interaction with the solar wind. Specifically, we compute the twin cell-vortical ionospheric flows, currents, and resulting radio powers resulting from a Dungey cycle process driven by dayside and nightside magnetic reconnection, as a function of planetary orbital distance and magnetic field strength. We include saturation of the magnetospheric convection, as observed at the terrestrial magnetosphere, and we present power law approximations for the convection potentials, radio powers and spectral flux densities. We specifically consider a solar-age system and a young (1 Gyr) system. We show that the radio power increases with magnetic field strength for magnetospheres with saturated convection potential, and broadly decreases with increasing orbital distance. We show that the magnetospheric convection at hot Jupiters will be saturated, and thus unable to dissipate the full av...

  4. Responses of the Equatorial Ionosphere to High Intensity Long Duration Continuous Auroral Activity

    Science.gov (United States)

    Sobral, J. H. A.; Abdu, M. A.; Gonzalez, W. D.; Gonzalez, A. C.; Tsurutani, B.; Daniela, D. C.; Arruda, C. S.

    This work focus the responses of the equatorial ionosphere over South America to intense substorms and, on the other hand, in the absence of magnetic storms. The substorms here concerned are related to what is known as High Intensity Long Duration Continuous Auroral Activity HILDCAA's. The analysis of these responses are carried out by means of ground-based ionosonde data from Fortaleza (3° 53'S 38° 25'W dip 2.7S for the epoch 1978-1979) and Cachoeira Paulista (22° 41'S , 45° 00W, dip 25.6S for 1978-1979)and ISEE-3 (Interplanetary Sun-Earth Explorer) satellite data during the 1978-1979 time frame. The substorm disturbed days are compared with the averages of quiet days. The ionospheric height variations are analyzed in the light of satellite data and intercomparisons of the two stations.

  5. Scintillation and loss of signal lock from poleward moving auroral forms in the cusp ionosphere

    CERN Document Server

    Oksavik, K; Lorentzen, D A; Baddeley, L J; Moen, J

    2016-01-01

    We present two examples from the cusp ionosphere over Svalbard,where poleward moving auroral forms (PMAFs) are causing significant phase scintillation in signals from navigation satellites. The data were obtained using a combination of ground-based optical instruments and a newly installed multiconstellation navigation signal receiver at Longyearbyen. Both events affected signals from GPS and Global Navigation Satellite System (GLONASS). When one intense PMAF appeared, the signal from one GPS spacecraft also experienced a temporary loss of signal lock. Although several polar cap patches were also observed in the area as enhancements in total electron content, the most severe scintillation and loss of signal lock appear to be attributed to very intense PMAF activity. This shows that PMAFs are locations of strong ionospheric irregularities, which at times may cause more severe disturbances in the cusp ionosphere for navigation signals than polar cap patches.

  6. Localized auroral disturbance in the morning sector of topside ionosphere as a standing electromagnetic wave

    Energy Technology Data Exchange (ETDEWEB)

    Dubinin, E.M.; Israelevich, P.L.; Nikolaeva, N.S.; Podgornyi, I.M.; Kutiev, I.

    1985-06-01

    The fine structure and plasma properties of an auroral disturbance observed with the Intercosmos-Bulgaria-1300 satellite are analyzed. The disturbance was detected in the morning sector of the sky at an altitude of about 850 km in December of 1981. Strong jumps (about 80 mV/m) in the electric and magnetic fields and fluctuations of ion density were detected within the disturbance. The electric and magnetic fields were characterized by a distinct spatial-temporal relationship typical for a standing quasi-monochromatic wave with a frequency of 1 Hz. The ratio of the amplitudes of electric and magnetic fluctuations was equal to the velocity of Alfven waves. The strong parallel component of the electric field (about 30 mV/m) and the large ion density of the fluctuations indicate changes in the plasma properties of the disturbance. The possibility of anomalous resistivity effects in the disturbance is also briefly considered. 23 references.

  7. Electromagnetic structures at auroral latitudes from luterkosmos-bolgariya-1300 satellite data

    Energy Technology Data Exchange (ETDEWEB)

    Dubinin, E.M.; Bankov, N.; Izraelevich, P.L.; Nikolaeva, N.S.; Podgornyi, I.M.; Todorieva, L.

    1986-11-01

    Strong electromagnetic disturbances in the auroral region at altitudes of about 900 km, which were recorded by the Interkosmos-Bolgariya-1300 satellite, are analyzed. An attempt is undertaken to determine general regularities in their structures. A specific class of events in which the disturbances of the electric and magnetic fields have the same form are distinguished. The events are a result of the propagation of oblique Alfven waves with lambda /sub z/ about 3.10 /sub s/ km, lambda /sub x/ less than or equal to 10 km, and f about 1 Hz. The lack of an apparent correlation between the mutually perpendicular components of the electric and magnetic fields is due to a significant phase shift between the disturbances of the electric and magnetic fields, which indicates the interference of the waves incident and reflected at the ionosphere.

  8. Auroral oval during a slightly disturbed period: electrodynamics of the midnight sector

    Energy Technology Data Exchange (ETDEWEB)

    Dubinin, E.M.; Izrailevich, P.L.; Kuz' min, A.K.; Nikolaeva, N.S.; Podgornyi, I.M.; Zaitsev, A.N.; Petrov, V.G.

    1987-09-01

    The authors present the results of measurements made on the satellite Interkosmos Bolgariya-1300: the measurements were of magnetic and electric fields, luminescence of the upper atmosphere, and the flux of precipitating particles near the midnight meridian. They compare the satellite data with magnetograms obtained simultaneously with ground stations. In the auroral zone, there exists a system of parallel plane sheets of field-aligned current. The sheets are elongated along bands of luminescence which coincide with them. Inside the current system, the plasma drifts eastward along the current sheets with a speed of several kilometers per second. The drift direction is in good agreement with the direction of the equivalent currents determined on the basis of the groundbased magnetograms. The position of the westward ionospheric Hall current agrees well with the position of the system of field-aligned currents. The maximum Hall current is situated between the major field-aligned currents.

  9. The Role of Auroral Imaging in Understanding Ionosphere-Inner Magnetosphere Interactions

    Science.gov (United States)

    Spann, Jim; Khazanov, George; Mende, Stephen

    2004-01-01

    The more ways we probe the ionosphere and inner magnetosphere, the better we can understand their interaction. For example, the multifaceted imaging of geospace with the IMAGE mission complements the more traditional in situ measurements made with many previous missions. Together they have enabled new knowledge of the ionosphere-magnetosphere (IM) coupling. The role of imaging the aurora in understanding this interaction has received renewed attention recently. Based on in situ data, such as FAST or DMSP, and our recent theories, we believe that imaging multiscale features of the aurora is a key component to gaining insight into the processes and mechanisms at work. This talk will explore how auroral imaging can be used to provide improved insight of the dynamics of IM interaction on micro and meso scales, with an emphasis on the current limitations and future possibilities of quantitative analyses.

  10. Explaining occurrences of auroral kilometric radiation in Van Allen radiation belts

    Science.gov (United States)

    Xiao, Fuliang; Zhou, Qinghua; Su, Zhenpeng; He, Zhaoguo; Yang, Chang; Liu, Si; He, Yihua; Gao, Zhonglei

    2016-12-01

    Auroral kilometric radiation (AKR) is a strong terrestrial radio emission and dominates at higher latitudes because of reflection in vicinities of the source cavity and plasmapause. Recently, Van Allen Probes have observed occurrences of AKR emission in the equatorial region of Earth's radiation belts but its origin still remains an open question. Equatorial AKR can produce efficient acceleration of radiation belt electrons and is a risk to space weather. Here we report high-resolution observations during two small storm periods 4-6 April and 18-20 May 2013 and show, using a 3-D ray tracing simulation, that AKR can propagate downward all the way into the equatorial plane in the radiation belts under appropriate conditions. The simulated results can successfully explain the observed AKR's spatial distribution and frequency range, and the current results have a wide application to all other magnetized astrophysical objects in the universe.

  11. Auroral streamers: characteristics of associated precipitation,convection and field-aligned currents

    Directory of Open Access Journals (Sweden)

    V. A. Sergeev

    2004-01-01

    Full Text Available During the long-duration steady convection activity on 11 December 1998, the development of a few dozen auroral streamers was monitored by Polar UVI instrument in the dark northern nightside ionosphere. On many occasions the DMSP spacecraft crossed the streamer-conjugate regions over the sunlit southern auroral oval, permitting the investigation of the characteristics of ion and electron precipitation, ionospheric convection and field-aligned currents associated with the streamers. We confirm the conjugacy of streamer-associated precipitation, as well as their association with ionospheric plasma streams having a substantial equatorward convection component. The observations display two basic types of streamer-associated precipitation. In its polewardmost half, the streamer-associated (field-aligned accelerated electron precipitation coincides with the strong (≥2–7μA/m2 upward field-aligned currents on the westward flank of the convection stream, sometimes accompanied by enhanced proton precipitation in the adjacent region. In the equatorward portion of the streamer, the enhanced precipitation includes both electrons and protons, often without indication of field-aligned acceleration. Most of these characteristics are consistent with the model describing the generation of the streamer by the narrow plasma bubbles (bursty bulk flows which are contained on dipolarized field lines in the plasma sheet, although the mapping is strongly distorted which makes it difficult to quantitatively interprete the ionospheric image. The convective streams in the ionosphere, when well-resolved, had the maximal convection speeds ∼0.5–1km/s, total field-aligned currents of a few tenths of MA, thicknesses of a few hundreds km and a potential drop of a few kV across the stream. However, this might represent only a small part of the associated flux transport in the equatorial plasma sheet.

    Key words. Ionosphere (electric fiels and

  12. Upstream drivers of poleward moving auroral forms by satellite-imager coordinated observations

    Science.gov (United States)

    Wang, B.; Nishimura, T.; Lyons, L. R.; Angelopoulos, V.; Frey, H. U.; Mende, S. B.

    2015-12-01

    Poleward moving auroral forms (PMAFs) are observed near the dayside poleward auroral oval boundary. PMAFs are thought to be an ionospheric signature of dayside reconnection and flux transfer events. PMAFs tend to occur when the IMF is southward. Although a limited number of PMAFs has been found in association with IMF southward turning, events without appreciable changes in IMF have also been reported. While those PMAFs could be triggered spontaneously, many of the past studies used solar wind measurements far away from the bow shock nose and may have used inaccurate time shift or missed small-scale structures in the solar wind. To examine how often PMAFs are triggered by upstream structures using solar wind measurements close to the bow shock nose, we use the AGO all sky imager in Antarctic and THEMIS B and C satellites in 2008, 2009 and 2011. We identified 24 conjunction events, where at least one of the THEMIS satellites is in the solar wind and the AGO imager is located within 3 MLT from the THEMIS MLT. We found that, in 14 out of 24 conjunction events, PMAFs occur soon after IMF southward turning, indicating that IMF southward turning could be the major triggering of PMAFs. Interestingly, among these 14 cases, there are 7 cases with different IMF structures between THEMIS B/C and OMNI, which obtained IMF information from WIND and ACE. And the larger correlation coefficients between PMAFs and IMFs observed by THMEIS B/C than OMNI present the advantages of THEMIS B/C. Among the 10 cases without correlating with IMF structures, PMAFs in two events are shown to have good correlation with reflected ions in the foreshock. Based on all the conjunction events we identified, IMF southward turning is the major trigger of PMAFs and reflected ions have minor effects. The rest of the cases could be spontaneous PMAFs, although foreshock activities, even if exists, may be missed due to the IMF orientation.

  13. Observations of nightside auroral plasma upflows in the F-region and topside ionosphere

    Directory of Open Access Journals (Sweden)

    C. Foster

    Full Text Available Observations from the special UK EISCAT program UFIS are presented. UFIS is a joint UHF-VHF experiment, designed to make simultaneous measurements of enhanced vertical plasma flows in the F-region and topside ionospheres. Three distinct intervals of upward ion flow were observed. During the first event, upward ion fluxes in excess of 1013 m–2 s–1 were detected, with vertical ion velocities reaching 300 m s–1 at 800 km. The upflow was associated with the passage of an auroral arc through the radar field of view. In the F-region, an enhanced and sheared convection electric field on the leading edge of the arc resulted in heating of the ions, whilst at higher altitudes, above the precipitation region, strongly enhanced electron temperatures were observed; such features are commonly associated with the generation of plasma upflows. These observations demonstrate some of the acceleration mechanisms which can exist within the small-scale structure of an auroral arc. A later upflow event was associated with enhanced electron temperatures and only a moderate convection electric field, with no indication of significantly elevated ion tem- peratures. There was again some evidence of F-region particle precipitation at the time of the upflow, which exhibited vertical ion velocities of similar magnitude to the earlier upflow, suggesting that the behaviour of the electrons might be the dominant factor in this type of event. A third upflow was detected at altitudes above the observing range of the UHF radar, but which was evident in the VHF data from 600 km upwards. Smaller vertical velocities were observed in this event, which was apparently uncorrelated with any features observed at lower altitudes. Limitations imposed by the experimental conditions inhibit the interpretation of this event, although the upflow was again likely related to topside plasma heating.

  14. Experimental investigation of auroral generator regions with conjugate Cluster and FAST data

    Directory of Open Access Journals (Sweden)

    O. Marghitu

    2006-03-01

    Full Text Available Here and in the companion paper, Hamrin et al. (2006, we present experimental evidence for the crossing of auroral generator regions, based on conjugate Cluster and FAST data. To our knowledge, this is the first investigation that concentrates on the evaluation of the power density, E·J, in auroral generator regions, by using in-situ measurements. The Cluster data we discuss were collected within the Plasma Sheet Boundary Layer (PSBL, during a quiet magnetospheric interval, as judged from the geophysical indices, and several minutes before the onset of a small substorm, as indicated by the FAST data. Even at quiet times, the PSBL is an active location: electric fields are associated with plasma motion, caused by the dynamics of the plasma-sheet/lobe interface, while electrical currents are induced by pressure gradients. In the example we show, these ingredients do indeed sustain the conversion of mechanical energy into electromagnetic energy, as proved by the negative power density, E·J<0. The plasma characteristics in the vicinity of the generator regions indicate a complicated 3-D wavy structure of the plasma sheet boundary. Consistent with this structure, we suggest that at least part of the generated electromagnetic energy is carried away by Alfvén waves, to be dissipated in the ionosphere, near the polar cap boundary. Such a scenario is supported by the FAST data, which show energetic electron precipitation conjugated with the generator regions crossed by Cluster. A careful examination of the conjunction timing contributes to the validation of the generator signatures.

  15. The thermospheric auroral red line polarization: confirmation of detection and first quantitative analysis

    Directory of Open Access Journals (Sweden)

    Moen Joran

    2013-01-01

    Full Text Available The thermospheric atomic oxygen red line is among the brightest in the auroral spectrum. Previous observations in Longyearbyen, Svalbard, indicated that it may be intrinsically polarized, but a possible contamination by light pollution could not be ruled out. During the winter 2010/2011, the polarization of the red line was measured for the first time at the Polish Hornsund polar base without contamination. Two methods of data analysis are presented to compute the degree of linear polarization (DoLP and angle of linear polarization (AoLP: one is based on averaging and the other one on filtering. Results are compared and are in qualitative agreement. For solar zenith angles (SZA larger than 108° (with no contribution from Rayleigh scattering, the DoLP ranges between 2 and 7%. The AoLP is more or less aligned with the direction of the magnetic field line, in agreement with the theoretical predictions of Bommier et al. (2010. However, the AoLP values range between ±20° around this direction, depending on the auroral conditions. Correlations between the polarization parameters and the red line intensity I were considered. The DoLP decreases when I increases, confirming a trend observed during the observations in Longyearbyen. However, for small values of I, DoLP varies within a large range of values, while for large values of I, DoLP is always small. The AoLP also varies with the red line intensity, slightly rotating around the magnetic field line.

  16. Separating spatial and temporal variations in auroral electric and magnetic fields by Cluster multipoint measurements

    Directory of Open Access Journals (Sweden)

    T. Karlsson

    2004-07-01

    Full Text Available Cluster multipoint measurements of the electric and magnetic fields from a crossing of auroral field lines at an altitude of 4RE are used to show that it is possible to resolve the ambiguity of temporal versus spatial variations in the fields. We show that the largest electric fields (of the order of 300mV/m when mapped down to the ionosphere are of a quasi-static nature, unipolar, associated with upward electron beams, stable on a time scale of at least half a minute, and located in two regions of downward current. We conclude that they are the high-altitude analogues of the intense return current/black auroral electric field structures observed at lower altitudes by Freja and FAST. In between these structures there are temporal fluctuations, which are shown to likely be downward travelling Alfvén waves. The periods of these waves are 20-40s, which is not consistent with periods associated with either the Alfvénic ionospheric resonator, typical field line resonances or substorm onset related Pi2 oscillations. The multipoint measurements enable us to estimate a lower limit to the perpendicular wavelength of the Alfvén waves to be of the order of 120km, which suggests that the perpendicular wavelength is similar to the dimension of the region between the two quasi-static structures. This might indicate that the Alfvén waves are ducted within a wave guide, where the quasi-static structures are associated with the gradients making up this waveguide.

  17. Electron dispersion events in the morningside auroral zone and their relationship with VLF emissions

    Energy Technology Data Exchange (ETDEWEB)

    Hardy, D.A.; Burke, W.J. (Hanscom Air Force Base, MA (United States)); Villalon, E. (Northeastern Univ., Boston, MA (United States))

    1990-05-01

    Energy/time dispersion events have been observed in the precipitating electron data in the energy range from 630 eV to 20 keV recorded by the J sensor on the low-altitude, polar-orbiting HILAT satellite. The dispersions are such that the higher-energy electrons are observed earlier in time than the lower-energy electrons The time interval for single dispersion event is from 1 to 2 s. Within an auroral pass in which such energy/time dispersion events are observed, there are typically several such events, and they can be spaced within the pass in either a periodic or aperiodic manner. The events are typically observed within and toward the equatorward edge of the region of diffuse auroral electron precipitation. During a given pass the events can be observed over a wide range of L shells. The occurrence of these events maximizes in the interval 0600-1,200 hours MLT. The energy/time dispersion is generally consistent with the electrons originating from a common source. The events are seen at L shells from 3.7 to greater than 15. The source distance for the electrons is inferred to be generally beyond the equator for events at L shells less than approximately 8 and before the equator for events at higher L shells. Because of the low energies at which the dispersions are observed, it is unlikely that their occurrence can be explained by resonant interaction with VLF waves. Based on circumstantial evidence from other reported observations common to the morning sector, and alternative theoretical explanation is presented. According to this model the dispersion events result from impulsive interactions of the electrons with intense, asymmetric packets of VLF waves via the nonlinear, ponderomotive force.

  18. Effect of excess superthermal hot electrons on finite amplitude ion-acoustic solitons and supersolitons in a magnetized auroral plasma

    Energy Technology Data Exchange (ETDEWEB)

    Rufai, O. R., E-mail: rrufai@csir.co.za [Council for Scientific and Industrial Research, Pretoria (South Africa); Bharuthram, R., E-mail: rbharuthram@uwc.ac.za [University of the Western Cape, Bellville (South Africa); Singh, S. V., E-mail: satyavir@iigs.iigm.res.in; Lakhina, G. S., E-mail: lakhina@iigs.iigm.res.in [Indian Institute of Geomagnetism, New Panvel (W), Navi, Mumbai-410218 (India)

    2015-10-15

    The effect of excess superthermal electrons is investigated on finite amplitude nonlinear ion-acoustic waves in a magnetized auroral plasma. The plasma model consists of a cold ion fluid, Boltzmann distribution of cool electrons, and kappa distributed hot electron species. The model predicts the evolution of negative potential solitons and supersolitons at subsonic Mach numbers region, whereas, in the case of Cairn's nonthermal distribution model for the hot electron species studied earlier, they can exist both in the subsonic and supersonic Mach number regimes. For the dayside auroral parameters, the model generates the super-acoustic electric field amplitude, speed, width, and pulse duration of about 18 mV/m, 25.4 km/s, 663 m, and 26 ms, respectively, which is in the range of the Viking spacecraft measurements.

  19. Axi-symmetric models of auroral current systems in Jupiter's magnetosphere with predictions for the Juno mission

    Directory of Open Access Journals (Sweden)

    S. W. H. Cowley

    2008-12-01

    Full Text Available We develop two related models of magnetosphere-ionosphere coupling in the jovian system by combining previous models defined at ionospheric heights with magnetospheric magnetic models that allow system parameters to be extended appropriately into the magnetosphere. The key feature of the combined models is thus that they allow direct connection to be made between observations in the magnetosphere, particularly of the azimuthal field produced by the magnetosphere-ionosphere coupling currents and the plasma angular velocity, and the auroral response in the ionosphere. The two models are intended to reflect typical steady-state sub-corotation conditions in the jovian magnetosphere, and transient super-corotation produced by sudden major solar wind-induced compressions, respectively. The key simplification of the models is that of axi-symmetry of the field, flow, and currents about the magnetic axis, limiting their validity to radial distances within ~30 RJ of the planet, though the magnetic axis is appropriately tilted relative to the planetary spin axis and rotates with the planet. The first exploration of the jovian polar magnetosphere is planned to be undertaken in 2016–2017 during the NASA New Frontiers Juno mission, with observations of the polar field, plasma, and UV emissions as a major goal. Evaluation of the models along Juno planning orbits thus produces predictive results that may aid in science mission planning. It is shown in particular that the low-altitude near-periapsis polar passes will generally occur underneath the corresponding auroral acceleration regions, thus allowing brief examination of the auroral primaries over intervals of ~1–3 min for the main oval and ~10 s for narrower polar arc structures, while the "lagging" field deflections produced by the auroral current systems on these passes will be ~0.1°, associated with azimuthal fields above the ionosphere of a few hundred nT.

  20. Radiation of auroral electrons and the dynamics of the magnetosphere. Rentgenovskoe izluchenie avroralnykh elektronov i dinamika magnitosfery

    Energy Technology Data Exchange (ETDEWEB)

    Lazutin, L.L.

    1979-01-01

    A detailed concept is given of methods employed for aerostatic measurements of inhibitory radiation of auroral electrons and accompanying geophysical phenomena in order to identify the physical nature of magnetic storms, aurora borealis, electron precipitation, and other manifestations of magnetospheric processes in turbulent periods. A summarization is given of aerostatic studies by Soviet and foreign experimental groups who have undertaken measurements in the high altitude stratosphere. 302 references, 89 figures, 3 tables.

  1. Intensity asymmetries in the dusk sector of the poleward auroral oval due to IMF $\\mathit{B}_{x}$

    CERN Document Server

    Reistad, J P; Laundal, K M; Haaland, S; Tenfjord, P; Snekvik, K; Oksavik, K; Milan, S E

    2016-01-01

    In the exploration of global-scale features of the Earth's aurora, little attention has been given to the radial component of the Interplanetary Magnetic Field (IMF). This study investigates the global auroral response in both hemispheres when the IMF is southward and lies in the $\\textit{xz}$ plane. We present a statistical study of the average auroral response in the 12-24 magnetic local time (MLT) sector to an $\\textit{x}$ component in the IMF. Maps of auroral intensity in both hemispheres for two IMF $\\mathit{B}_{x}$ dominated conditions($ \\pm $ IMF $\\mathit{B}_{x}$) are shown during periods of negative IMF $\\mathit{B}_{z}$, small IMF $\\mathit{B}_{y}$, and local winter. This is obtained by using global imaging from the Wideband Imaging Camera on the IMAGE satellite. The analysis indicates a significant asymmetry between the two IMF $\\mathit{B}_{x}$ dominated conditions in both hemispheres. In the Northern Hemisphere the aurora is brighter in the 15-19 MLT region during negative IMF $\\mathit{B}_{x}$. In th...

  2. Ion acoustic instability of HPT particles, FAC density, anomalous resistivity and parallel electric field in the auroral region

    Indian Academy of Sciences (India)

    C S Jayasree; G Renuka; C Venugopal

    2003-12-01

    During the magnetic storm of 21st March 1990, the DE-1 spacecraft encountered the auroral region at high invariant latitude at altitudes ranging from a few thousand kilometers in the ionosphere to many earth radii in the magnetosphere. The magnetic field perturbations interpretable as field aligned current (FAC) layers and the electrostatic turbulence possibly due to electrostatic ion acoustic instability driven by these currents are shown. The critical drift velocity of Hot Plasma Torus (HPT) electrons and the growth rate of ion acoustic wave as a function of electron to ion temperature ratio (/) for low and high current densities and energy of HPT electrons are found out. The intense FAC destabilizes the ion acoustic wave and the resultant electrostatic turbulence creates an anomalous resistivity. The current driven resistivity produces parallel electric field and high power dissipation. The anomalous resistivity , potential differnece along the auroral field lines ∥, intensity of electric field turbulence ∥ and power produced per unit volume are computed. It is found that the change in westward magnetic perturbation increases ∥; ; ∥ ;∥ and . Hence HPT electrons are heated and accelerated due to power dissipation during magnetically active periods in the auroral region. Concerning, applications, such HPT electrons can be used in particle accelerators like electron ring accelerator, smokatron etc.

  3. Current-voltage and kinetic energy flux relations for relativistic field-aligned acceleration of auroral electrons

    Directory of Open Access Journals (Sweden)

    S. W. H. Cowley

    2006-03-01

    Full Text Available Recent spectroscopic observations of Jupiter's "main oval" auroras indicate that the primary auroral electron beam is routinely accelerated to energies of ~100 keV, and sometimes to several hundred keV, thus approaching the relativistic regime. This suggests the need to re-examine the classic non-relativistic theory of auroral electron acceleration by field-aligned electric fields first derived by Knight (1973, and to extend it to cover relativistic situations. In this paper we examine this problem for the case in which the source population is an isotropic Maxwellian, as also assumed by Knight, and derive exact analytic expressions for the field-aligned current density (number flux and kinetic energy flux of the accelerated population, for arbitrary initial electron temperature, acceleration potential, and field strength beneath the acceleration region. We examine the limiting behaviours of these expressions, their regimes of validity, and their implications for auroral acceleration in planetary magnetospheres (and like astrophysical systems. In particular, we show that for relativistic accelerating potentials, the current density increases as the square of the minimum potential, rather than linearly as in the non-relativistic regime, while the kinetic energy flux then increases as the cube of the potential, rather than as the square.

  4. The presence of large sunspots near the central solar meridian at the times of modern Japanese auroral observations

    Directory of Open Access Journals (Sweden)

    D. M. Willis

    2006-10-01

    Full Text Available The validity of a technique developed by the authors to identify historical occurrences of intense geomagnetic storms, which is based on finding approximately coincident observations of sunspots and aurorae recorded in East Asian histories, is corroborated using more modern sunspot and auroral observations. Scientific observations of aurorae in Japan during the interval 1957–2004 are used to identify geomagnetic storms that are sufficiently intense to produce auroral displays at low geomagnetic latitudes. By examining white-light images of the Sun obtained by the Royal Greenwich Observatory, the Big Bear Solar Observatory, the Debrecen Heliophysical Observatory and the Solar and Heliospheric Observatory spacecraft, it is found that a sunspot large enough to be seen with the unaided eye by an "experienced" observer was located reasonably close to the central solar meridian immediately before all but one of the 30 distinct Japanese auroral events, which represents a 97% success rate. Even an "average" observer would probably have been able to see a sunspot with the unaided eye before 24 of these 30 events, which represents an 80% success rate. This corroboration of the validity of the technique used to identify historical occurences of intense geomagnetic storms is important because early unaided-eye observations of sunspots and aurorae provide the only possible means of identifying individual historical geomagnetic storms during the greater part of the past two millennia.

  5. The peak altitude of H3+ auroral emission: comparison with the ultraviolet

    Science.gov (United States)

    Blake, J.; Stallard, T.; Miller, S.; Melin, H.; O'Donoghue, J.; Baines, K.

    2013-09-01

    The altitude of Saturn's peak auroral emission has previously been measured for specific cases in both the ultraviolet (UV) and the infrared (IR). Gerard et al [2009] concludes that the night side H2 UV emission is within the range of 800 to 1300 km above the 1-bar pressure surface. However, using colour ratio spectroscopy, Gustin et al [2009] located the emission layer at or above 610 km. Measurements of the infrared auroral altitude was conducted by Stallard et al [2012] on H3+ emissions from nine VIMS Cassini images, resulting in a measurement of 1155 ± 25 km above the 1-bar pressure surface. Here we present data analysed in a manner similar to Stallard et al [2012] on the observations of H3+ emission in twenty images taken by the Visual Infrared Mapping Spectrometer (VIMS) aboard the spacecraft Cassini from the years 2006, 2008 and 2012. The bins covered were 3.39872, 3.51284, 3.64853, 4.18299 and 4.33280 μm. These observations were selected from a set of 15,000 as they contained a useful alignment of the aurorae on the limb and the body of the planet. The specific conditions that had to be met for each image were as follows; minimum integration time of 75 milliseconds per pixel, minimum number of pixels in the x and y direction of 32, the image must include the latitude range of 70 to 90 degrees for either hemisphere and the sub spacecraft angle must be between 0 and 20 degrees. This alignment allowed for the altitudinal profiles to be analysed in terms of the difference between the latitude of aurorae on the limb and on the body of Saturn; thus permitting an investigation into the effects of misalignment. In this instance, misalignment was defined as the difference between the latitude of the peak emission latitude on the planet and the latitude of the limb; assuming the aurorae to be approximately circular. A statistical study by Badman et al [2011] showed that centre of the oval is on average offset anti sunward of the pole by about 1.6 degrees. To

  6. Automatic Georeferencing of Astronaut Auroral Photography: Providing a New Dataset for Space Physics

    Science.gov (United States)

    Riechert, Maik; Walsh, Andrew P.; Taylor, Matt

    2014-05-01

    Astronauts aboard the International Space Station (ISS) have taken tens of thousands of photographs showing the aurora in high temporal and spatial resolution. The use of these images in research though is limited as they often miss accurate pointing and scale information. In this work we develop techniques and software libraries to automatically georeference such images, and provide a time and location-searchable database and website of those images. Aurora photographs very often include a visible starfield due to the necessarily long camera exposure times. We extend on the proof-of-concept of Walsh et al. (2012) who used starfield recognition software, Astrometry.net, to reconstruct the pointing and scale information. Previously a manual pre-processing step, the starfield can now in most cases be separated from earth and spacecraft structures successfully using image recognition. Once the pointing and scale of an image are known, latitudes and longitudes can be calculated for each pixel corner for an assumed auroral emission height. As part of this work, an open-source Python library is developed which automates the georeferencing process and aids in visualization tasks. The library facilitates the resampling of the resulting data from an irregular to a regular coordinate grid in a given pixel per degree density, it supports the export of data in CDF and NetCDF formats, and it generates polygons for drawing graphs and stereographic maps. In addition, the THEMIS all-sky imager web archive has been included as a first transparently accessible imaging source which in this case is useful when drawing maps of ISS passes over North America. The database and website are in development and will use the Python library as their base. Through this work, georeferenced auroral ISS photography is made available as a continously extended and easily accessible dataset. This provides potential not only for new studies on the aurora australis, as there are few all-sky imagers in

  7. Sounding-Rocket Studies of Langmuir-Wave Microphysics in the Auroral Ionosphere

    Science.gov (United States)

    Dombrowski, Micah P.

    Since their discovery in laboratory plasmas in the 1920s, Langmuir waves have been observed to be ubiquitous in plasma environments, particularly in space plasmas. From the greater solar wind to planetary foreshocks and the auroral ionosphere, Langmuir waves are a key factor mediating electron temperature, and controlling electron beam propagation and beam-plasma energy transfer. Because they are so important, Langmuir waves in the space environment have been intensively investigated; however, there remain two challenging types of experiments that are relatively lacking: three-dimensional measurements of Langmuir-wave fields, and measurements of Langmuir wave-electron correlations. This thesis works on filling these two gaps, plus development of new Langmuir-wave instrumentation. The CHARM-II wave-particle Correlator instrument was designed to study the energy transfer between electron beams and plasmas via the sorting of incoming particles by concurrent Langmuir-wave phase, allowing for direct observation of electron bunching. Data from the CHARM-II sounding rocket comprises the first such observations with statistical levels of events, revealing an association between the polarity of the resistive component of the electron phase-bunching and changes in the electron flux at the associated energy, such that a negative resistive component goes with an increase in electron flux, and vice versa, effectively showing energy flow from the beam to the waves, and subsequent enhancements of wave damping. Surprisingly, the results also show comparable amounts of resistive and reactive activity. A test-particle simulation was developed to confirm the details of the theoretical explanation for the observed effect. A three-dimensional Langmuir-wave receiver flown on the TRICE sounding rocket mission reveals the beat signature of the amplitude-modulated 'bursty' form of Langmuir waves which has been observed in many environments. An analysis of the three-dimensional data shows

  8. Use of Auroral Processes in Spacecraft Propulsion: A VASIMR VX-100 Status Report

    Science.gov (United States)

    Brukardt, M.; Bering, E. A.; Chang-Diaz, F. R.; Squire, J. P.; Glover, T. W.; Cassady, L. D.; Jacobson, V. T.; Chancery, W. J.; Longmier, B. W.

    2007-12-01

    Plasma physics has found an increasing range of practical industrial applications, including the development of electric spacecraft propulsion systems. One of these systems, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine, applies several important physical processes occurring in the magnetosphere. These processes include the mechanisms involved in the ion acceleration and heating that occur in the Birkeland currents of an auroral arc system. Auroral current region processes that are applied in VASIMR include lower hybrid heating, parallel electric field acceleration and ion cyclotron acceleration. This paper will focus on using two physics demonstration model VASIMR's to study ion cyclotron heating (ICRH). Prior to VASIMR, laboratory simulation of electromagnetic ion cyclotron wave heating has been difficult owing to the difficulty in obtaining efficient antenna coupling for this mode and to the fact that the ions involved only pass through the acceleration region once. The VX-50 and VX-100 VASIMR's use(d) a helicon antenna with 20 kW of power to generate plasma. Both devices then use(d) an RF booster stage that uses left hand polarized slow mode waves launched from the high field side of the resonance. The VX-50 used 2 to 4 MHz waves with 30 kW of power. The VX-100 operates at ~500 kHz, with up to 100 kW of available ICRH power. This paper will summarize results from high power ICRH experiments performed on the VX-50 using deuterium, neon and argon plasma during 2006 and will present preliminary results from the VX-100. Emphasis will be placed on results obtained since the last Fall meeting We have demonstrated ion cyclotron acceleration of a dense (>1019/m3) plasma flow using all three gasses. ICRH loading measurements are consistent with efficient (90%) RF coupling to the plasma. The ICRH experiments have demonstrated that an energy boost of over 500 eV is possible. Early VX-100 results indicate that it should be possible to obtain an exhaust

  9. Interferometric radar observations of filamented structures due to plasma instabilities and their relation to dynamic auroral rays

    Directory of Open Access Journals (Sweden)

    T. Grydeland

    2004-04-01

    Full Text Available Several explanations have been proposed for Naturally Enhanced ion-acoustic Echoes observed at mid- and high-latitude Incoherent Scatter observatories. A decisive measure for distinguishing between these explanations is whether or not simultaneously observed up- and down-shifted enhancement occur simultaneously, or if they are the result of temporal and/or spatial averaging.

    The EISCAT Svalbard Radar has two antennas in the same radar system, which can be used as an interferometer when pointed parallel. In observations from 17 January 2002, between 06:46:10 and 06:46:30 UT, we used this possibility, in combination with direct sampling of the received signals, to yield measurements of "naturally enhanced ion-acoustic echoes" with sufficiently high resolution to resolve such averaging, if any. For the first time, radar interferometry has been employed to estimate the sizes of coherent structures. The observations were coordinated with an image intensified video camera with a narrow field of view. Together, this forms the initial study on the causal relationships between enhanced echoes and fine structure in the auroral activity on sub-kilometer, sub-second scales.

    The results confirm that the enhanced echoes originate from very localised regions (~300m perpendicular to the magnetic field at 500km altitude with varying range distribution, and with high time variability (≈200ms. The corresponding increase in scattering cross section, up to 50dB above incoherent scattering, eliminates theoretical explanations based on marginal stability. The simultaneously observed up- and down-shifted enhanced shoulders, when caused by sufficiently narrow structures to be detected by the interferometer technique, originate predominantly from the same volume. These results have significant impact on theories attempting to explain the enhancements, in particular it is found that the ion

  10. The MITHRAS: A program of simultaneous radar observations of the high-latitude auroral zone

    Science.gov (United States)

    Delabeaujardiere, O.; Baron, M. J.; Wickwar, V. B.; Senior, C.; Evans, J. V.

    1982-11-01

    An intensive campaign of coordinated incoherent-scatter radar experiments took place in 1981-1982. It was planned to take advantage of the short period during which three incoherent-scatter radars could probe the auroral zone simultaneously. The three incoherent-scatter radars that participated in the MITHRAS experiments were Chatanika, Millstone-Hill, and EISCAT. Collaborative studies were undertaken using data from the DE spacecraft and the stare radar. There were three main types of MITHRAS experiments, each with a different scientific purpose. MITHRAS 1 was aimed at large latitudinal coverage of F-region drifts, electron-densities and temperatures. MITHRAS 2 was designed for very good height and time resolution. MITHRAS 3 was intermediate between the other two modes. It provided both E- and F-region coverage over several degrees in latitude. Under the MITHRAS project, substantial changes and additions were made to the software and hardware systems at Millstone and Chatanika. Thirty-three MITHRAS experiments were performed. Most of the data have been reduced. The analysis and interpretation of the date are well underway.

  11. Negative ions in the auroral mesosphere during a PCA event around sunset

    Directory of Open Access Journals (Sweden)

    C. F. del Pozo

    Full Text Available This is a study of the negative ion chemistry in the mesosphere above Tromsø using a number of EISCAT observations of high energy proton precipitation events during the last solar maximum, and in particular around sunset on 23 October, 1989. In these conditions it is possible to look at the relative importance of the various photodetachment and photodissociation processes controlling the concentration of negative ions. The data analysed are from several UHF GEN11 determinations of the ion-plasma ACF together with the pseudo zero-lag estimate of the `raw' electron density, at heights between 55 km and 85 km, at less than 1 km resolution. The power profiles from the UHF are combined with the 55-ion Sodankylä model to obtain consistent estimates of the electron density, the negative ion concentrations, and the average ion mass with height. The neutral concentrations and ion temperature are given by the MSIS90 model. These parameters are then used to compare the calculated widths of the ion-line with the GEN11 determinations. The ion-line spectrum gives information on the effects of negative ions below 70 km where they are dominant; the spectral width is almost a direct measure of the relative abundance of negative ions.

    Key words. Ionosphere (auroral ionosphere; ion chemistry and composition; particle precipitation.

  12. Naturally enhanced ion acoustic waves in the auroral ionosphere observed with the EISCAT 933-MHz radar

    Energy Technology Data Exchange (ETDEWEB)

    Rietveld, M.T. (EISCAT, Ramfjordbotn (Norway)); Collis, P.N. (EISCAT, Kiruna (Sweden)); St.Maurice, J.P. (Univ. of Western Ontario, London (Canada))

    1991-11-01

    Observations of strongly enhanced ion acoustic shoulders of the incoherent scatter spectrum at 933 MHz at altitudes from 138 to 587 km have been obtained with the European Incoherent Scatter UHF radar. The enhancements can be up to 1 or 2 orders of magnitude in total backscattered power and can occur at either one or both of the ion acoustic shoulders. They show a variation of frequency with height of about 2 to 1, the same as the normal ion line spectral width and the ion temperature. These unusual spectra appear in two preferred height regions having different characteristics, one below 200 km and one above about 300 km. The enhancements are associated with geomagnetic disturbance, high electron temperatures, auroral arcs, and red aurora in the F region. The observations, which are mainly along the magnetic field direction, indicate that field-aligned thermal electron drifts are destabilizing the ion acoustic waves. The confirm and extend the one other publication reporting on similar echoes. The authors suggest that field-aligned flows of soft electrons depositing their energy at horizontally poor conducting F region heights are the cause of parallel electric fields in the ionosphere. These fields then produce the thermal electron motions that they argue have to be the cause of the observations.

  13. A localised co-rotating auroral absorption event observed near noon using imaging riometer and EISCAT

    Directory of Open Access Journals (Sweden)

    P. N. Collis

    Full Text Available An isolated region of energetic electron precipitation observed near local noon in the auroral zone has been investigated using imaging riometer (IRIS and incoherent-scatter radar (EISCAT techniques. IRIS revealed that the absorption event was essentially co-rotating with the Earth for about 2 h. The spatial and temporal variations in D-region electron density seen by EISCAT were able to be interpreted within a proper context when compared with the IRIS data. EISCAT detected significant increases in electron density at altitudes as low as 65 km as the event drifted through the radar beam. The altitude distribution of incremental radio absorption revealed that more than half of the absorption occurred below 75 km, with a maximum of 67 km. The energy spectrum of the precipitating electrons was highly uniform throughout the event, and could be described analytically by the sum of three exponential distributions with characteristic energies of 6, 70 and 250 keV. A profile of effective recombination coefficient that resulted in self-consistent agreement between observed electron desities and those inferred from an inversion procedure has been deduced. The observations suggest a co-rotating magnetospheric source region on closed dayside field lines. However, a mechanism is required that can sustain such hard precipitation for the relatively long duration of the event.

  14. GEOS-2 observations of energetic electrons in the morning sector during auroral radio absorption events

    Energy Technology Data Exchange (ETDEWEB)

    Collis, P.N.; Korth, A.

    1985-04-01

    The temporal development of two auroral absorption events in the morning sector is compared with simultaneous observations of electrons from the satellite GEOS-2, utilizing the good energy resolution over the range 15-300 keV to show that the electrons effective in contributing to the observed radio absorption are confined to the range 30-130 keV. By far the most important are those below 80 keV, and as a geophysical monitor the riometer may be considered an efficient indicator of electron fluxes of energy typically of 60-70 keV. The ionospheric effects of the precipitated fluxes are predicted, and the results used to discuss the validity of the model atmosphere and of the profiles of effective recombination coefficient and specific absorption. Integration of the calculated profiles of incremental radio absorption yields total estimates within 30 percent of the observed intensities. The absorbing layer maximizes at altitudes of 85-90 km and has a typical half-height of 25 km. It is shown further that the electron-flux characteristics are consistent with gradient-curvature drift from a particle source in the midnight sector. 33 references.

  15. Loss cone fluxes and pitch angle diffusion at the equatorial plane during auroral radio absorption events

    Energy Technology Data Exchange (ETDEWEB)

    Collis, P.N.; Hargreaves, J.K.

    1983-04-01

    Flux and pitch angle distributions of energetic electrons at geostationary altitude in the vicinity of the atmospheric loss cone associated with an auroral radio absorption event are investigated. Measurements were made in the energy range 15-300 keV by the medium energy charged particle spectrometer on board the GEOS-2 satellite at the times of absorption events detected near the predicted foot of the geomagnetic field line passing through the satellite. Comparisons with theoretical pitch angle distributions and recombination rates indicate pitch angle diffusion coefficients to be 0.001/sec for a 2-dB event and 0.0001/sec for a 1-dB event. Further comparisons of the average electron measurements in the pitch angle range 0-5 deg with observations of the radio absorption by the portion of this flux which is actually precipitated are used to deduce the degree of departure of the electron pitch angle distribution from isotropy, and to place limits upon the ranges of effective recombination rate profiles. An empirical relation is derived which allows radio absorption to be predicted from measured electron fluxes.

  16. Langmuir turbulence in the auroral ionosphere 2: Nonlinear theory and simulations

    Science.gov (United States)

    Newman, D. L.; Goldman, M. V.; Ergun, R. E.

    1994-01-01

    A theoretical interpretation of sounding rocket measurements of intense Langmuir wave fields (less than or equal to 500 mV/m) driven by a stream of 20 eV to 4 keV electrons in the lower auroral zone is developed. This interpretation is based on the ability of the 10 microseconds sampling rate of the wave detector to temporally resolve the structure of the Langmuir wave field envelope. A modified form of the Zakharov equations is used to numerically study beam-driven Langmuir turbulence in the presence of a moderate magnetic field (OMEGA (sub e) approximately equals Omega (sub pe). Strong Landau damping on observed nonthermal scattered electrons, which is treated in a companion paper (Newman et al., this issue), plays an important role by inhibiting backscatter cascade and the development of strong turbulence. A parameterized model of the linear electron stream-driven wave instability is introduced, which incorporates limited quasilinear plateau formation. A reasonable set of parameters is found that yields semiquantitative agreement between observed properties of the Langmuir fields and the results of Zakharov equation simulations, including the amplitude and characteristic frequency of the electric field envelope modulations.

  17. Numerical study of the auroral particle transport in the polar upper atmosphere

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Starting from the Boltzmann equation and with some reasonable assumptions, a one-dimensional transport equation of charged energetic particles is derived by taking account of major interactions with neutral species in the upper atmosphere, including the processes of elastic scattering, the excitation, the ionization and the secondary electron production. The transport equation is numerically solved, for a simplified atmosphere consisting only of nitrogen molecules (N2), to obtain the variations of incident electron fluxes as a function of altitude, energy and pitch angle. The model results can describe fairly the transport characteristics of pre-cipitating auroral electron spectra in the polar upper atmosphere; meanwhile the N2 ionization rates calculated from the modeled differential flux spectra also exhibit good agreements with existing empirical models in terms of several key parameters. Taking the energy flux spectra of precipitating electrons observed by FAST satellite flying over EISCAT site on May 15, 1997 as model inputs, the model-calculated ionization rate profile of neutral atmosphere consists reasonably with that recon-structed from electron density measurements by the radar.

  18. Upper atmospheric effects of the hf active auroral research program ionospheric research instrument (HAARP IRI)

    Energy Technology Data Exchange (ETDEWEB)

    Eccles, V.; Armstrong, R.

    1993-05-01

    The earth's ozone layer occurs in the stratosphere, primarily between 10 and 30 miles altitude. The amount of ozone, O3, present is the result of a balance between production and destruction processes. Experiments have shown that natural processes such as auroras create molecules that destroy O. One family of such molecules is called odd nitrogen of which nitric oxide (NO) is an example. Because the HAARP (HF Active Auroral Research Program) facility is designed to mimic and investigate certain natural processes, a study of possible effects of HAARP on the ozone layer was conducted. The study used a detailed model of the thermal and chemical effects of the high power HF beam, which interacts with free electrons in the upper atmosphere above 50 miles altitude. It was found only a small fraction of the beam energy goes into the production of odd nitrogen molecules, whereas odd nitrogen is efficiently produced by auroras. Since the total energy emitted by HAARP in the year is some 200,000 times less than the energy deposited in the upper atmosphere by auroras, the study demonstrates that HAARP HF beam experiments will cause no measurable depletion of the earth's ozone layer.... Ozone, Ozone depletion, Ozone layer, Odd nitrogen, Nitric oxide, HAARP Emitter characteristics.

  19. Magnetic Storm Effects in the Auroral Ionosphere Observed with EISCAT Radar -Two Case Studies

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Storm-time changes of main plasma parameters in the auroral ionosphere are analyzed for two intense storms occurring on May 15, 1997 and Sept. 25, 1998, with emphasis on their relationship to the solar wind dynamic pressure and the IMF Bz component. Strong hard particle precipitation occurred in the initial phase for both storma,associated with high solar wind dynamical pressure. During the recovery phase of the storms, some strong particle precipitation was neither concerned with high solar wind pressure nor southward IMF Bz. Severe negative storm effects depicted by electron density depletion appeared in theF-region during the main and recovery phase of both storms, caused by intensive electric field-related strong Joule/frictional heating when IMF was largely southward. The ion temperature behaved similarly in E- and F-region, but the electron temperature did quite different, with a strong increase in the lower E-region relating to plasma instability excited by strong electric field and a slight decrease in the F-region probably concerning with a cooling process. The field-aligned ion velocity was high and apparently anticorrelated with the northward component of the ion convection velocity.

  20. Sheared magnetospheric plasma flows and discrete auroral arcs: a quasi-static coupling model

    Directory of Open Access Journals (Sweden)

    M. M. Echim

    2007-02-01

    Full Text Available We consider sheared flows in magnetospheric boundary layers of tangential discontinuity type, forming a structure that is embedded in a large-scale convergent perpendicular electric field. We construct a kinetic model that couples the magnetospheric structure with the topside ionosphere. The contribution of magnetospheric electrons and ionospheric electrons and ions is taken into account into the current-voltage relationship derived for an electric potential monotonically decreasing with the altitude. The solution of the current continuity equation gives the distribution of the ionospheric potential consistent with the given magnetospheric electric potential. The model shows that a sheared magnetospheric flow generates current sheets corresponding to upward field-aligned currents, field-aligned potential drops and narrow bands of precipitating energy, as in discrete auroral arcs. Higher velocity magnetospheric sheared flows have the tendency to produce brighter and slightly broader arcs. An increase in arc luminosity is also associated with enhancements of magnetospheric plasma density, in which case the structures are narrower. Finally, the model predicts that an increase of the electron temperature of the magnetospheric flowing plasma corresponds to slightly wider arcs but does not modify their luminosity.

  1. Tests of Sunspot Number Sequences: 2. Using Geomagnetic and Auroral Data

    CERN Document Server

    Lockwood, Mike; Barnard, Luke A; Scott, Chris J; Usoskin, Ilya G; Nevanlinna, Heikki

    2016-01-01

    We compare four sunspot-number data sequences against geomagnetic and terrestrial auroral observations. The comparisons are made for the original SIDC composite of Wolf-Zurich-International sunspot number [$R_{ISNv1}$], the group sunspot number [$R_{G}$] by Hoyt and Schatten (Solar Phys., 1998), the new "backbone" group sunspot number [$R_{BB}$] by Svalgaard and Schatten (Solar Phys., 2016), and the "corrected" sunspot number [$R_{C}$] by Lockwood at al. (J.G.R., 2014). Each sunspot number is fitted with terrestrial observations, or parameters derived from terrestrial observations to be linearly proportional to sunspot number, over a 30-year calibration interval of 1982-2012. The fits are then used to compute test sequences, which extend further back in time and which are compared to $R_{ISNv1}$, $R_{G}$, $R_{BB}$, and $R_{C}$. To study the long-term trends, comparisons are made using averages over whole solar cycles (minimum-to-minimum). The test variations are generated in four ways: i) using the IDV(1d) an...

  2. Right-hand polarized 4fce auroral roar emissions: 1. Observations

    Science.gov (United States)

    LaBelle, J.; Chen, Y.

    2016-08-01

    A receiving system installed at Sondrestrom, Greenland, was used to monitor all detectable auroral radio emissions at the fourth harmonic of the electron cyclotron frequency (called 4fce roar emissions) between May 2015 and March 2016. Of 88 events detected, 86 occurred during daylit conditions and were left-hand polarized. Two occurred during darkness conditions and were right-hand polarized. The left-hand and right-hand polarized events had entirely different frequency distributions. One of the right-hand polarized 4fce emissions occurred at the same time as and at exactly twice the frequency of a second harmonic emission (2fce roar). The occurrence rate of 4fce emissions during premidnight hours under daylit conditions at Sondrestrom is 5%, comparable to previously reported occurrence rates of 2fce roar in darkness conditions at optimum latitudes of occurrence, but the occurrence rate of 4fce emissions during dark conditions is much lower, suggesting that if the right-hand polarized events arise from coalescence of 2fce waves, only for a small fraction of nighttime 2fce roar emissions does such a process yield 4fce emissions detectable at ground level.

  3. A Network of Small Spacecraft for Multipoint Measurement of Auroral Plasma

    Science.gov (United States)

    Roberts, T. Maximillian; Lynch, Kristina; Clayton, Robert; Hampton, Donald

    2016-10-01

    Measurement of ionospheric plasma is often performed by a single in-situ device, or remotely using cameras and radar. This constrains determination of small scale variation in plasma structure to somewhat restrictive assumptions. We have developed and tested a local, multipoint measurement system composed of a network of small spacecraft which are ejected from a main payload carried by sounding rocket. The low-resource, spin-stabilized projectiles radio measurements to the main payload for transmission to ground. Measurements from an onboard LED array and IMU are used to determine the separation of the devices from the main payload and orientation relative to the geomagnetic field. The primary measurements are made by two orthogonal retarding potential analyzers on each spacecraft, allowing for determination of local ion parameters. A test flight in October 2015 demonstrated the successful application of this system, as well as revealing several important design issues. This work is in preparation for the February 2017 ISINGLASS sounding rocket mission to study the gradient scale lengths in auroral plasma, involving the deployment of two of these spacecraft networks. Supported by NASA Grants NNX14AH07G and NNX15AK51A.

  4. Investigation of triggering of poleward moving auroral forms using satellite-imager coordinated observations

    Science.gov (United States)

    Wang, Boyi; Nishimura, Yukitoshi; Zou, Ying; Lyons, Larry R.; Angelopoulos, Vassilis; Frey, Harald; Mende, Stephen

    2016-11-01

    Poleward moving auroral forms (PMAFs) are thought to be an ionospheric signature of dayside magnetic reconnection. While PMAFs are more likely to occur when the interplanetary magnetic field (IMF) is southward, how often PMAFs are triggered by changes in solar wind parameters is still an open question. To address this issue, we used one of the Automatic Geophysical Observatories all-sky imagers in Antarctica and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C satellites, which can give solar wind measurements much closer to the subsolar bow shock than by Wind or ACE, to examine if PMAFs occurred in association with IMF orientation changes. We identified 60 PMAFs in conjunction with THEMIS B and C during 2008, 2009, and 2011 and 70% of events show reduction of Bz before PMAF onset indicating that IMF southward turning plays an important role in triggering a majority of PMAFs. In contrast, the magnitude of the IMF Bz reduction in OMNI data was smaller and the reduction occurred in a slightly smaller percentage of events (40-60%). This suggests that solar wind structures that missed the L1 point or evolution of solar wind between the L1 point and THEMIS may be important for identifying IMF changes responsible for transient dayside reconnection. Additionally, 17 PMAFs that did not have substantial IMF southward turnings are correlated well with foreshock events, indicating that foreshock phenomena may also play a role in triggering PMAFs.

  5. Ponderomotive effects on distributions of O(+) ions in the auroral zone

    Science.gov (United States)

    Witt, E.; Hudson, M. K.; Li, X.; Roth, I.; Temerin, M.

    1995-01-01

    Test particle calculations are used to compute the effects of gravity and ponderomotive acceleration by shear Alfven wave oscillations on the distribution function of O(+) ions along auroral field lines, assuming an ionospheric Maxwellian source of the ions at 2000 km altitude with approximately 0.5 eV of thermal energy in the parallel component of velocity. The electric field model corresponds to a standing wave oscillation with a frequency approximately 1 Hz in the azimuthal direction superimposed on the background dipole field, in which the wave amplitude is either increasing or decreasing in time. The electric field is taken to be primarily in the perpendicular direction. The time varying wave produces broad distributions with widths of 2 to 10 times the initial 0.5-eV thermal energy of the Maxwellian source, and the density and flux of upward going O(+) ions at one Earth radius are both enhanced in this model. The oxygen ion distribution functions at 1 R(sub E) altitude resulting from interaction with waves whose amplitudes are increasing in time have a more gradual lower energy cutoff than do the distribution functions resulting from decaying waves. The high-energy part of the distribution functions in growing waves reflects the temperature of the Maxwellian source, while the high-energy part of the distributions resulting from decaying waves steepens with time, independent of the source temperature.

  6. Fine structures and dynamics in auroral initial brightening at substorm onsets

    Directory of Open Access Journals (Sweden)

    K. Sakaguchi

    2009-02-01

    Full Text Available We show four auroral initial brightening events at substorm onsets focusing on fine structures and their longitudinal dynamics, which were observed by all-sky TV cameras (30-Hz sampling on January 2008, in Canada. For two initial brightenings started in the field of views of the cameras, we found that they started at longitudinal segments with a size of less than ~30–60 km. One brightening expanded with wavy structures and the other expanded as a straight arc. Although the two events had different structures, both brightening auroras expanded with an average speed of ~20 km/s in the first 10 s, and ~10 km/s in the following 10 s. The other two events show that brightening auroras developed with periodic structures, with longitudinal wavelengths of ~100–200 km. Assuming that the brightening auroras are mapped to the physical processes occurring in the plasma sheet, we found that the scale size (30–60 km and the expanding speed (20 km/s of brightening auroras correspond to the order of ion gyro radii (~500–1400 km and Alfvén speed or fast ion-flow speed (~400 km/s, respectively, in the plasma sheet.

  7. Ion heating by strong electrostatic ion cyclotron turbulence. [in auroral zone

    Science.gov (United States)

    Lysak, R. L.; Hudson, M. K.; Temerin, M.

    1980-01-01

    A theory of the ion heating due to electrostatic ion cyclotron (EIC) waves in the auroral zone is presented. Due to the slowly convecting nature of the EIC mode, quasi-linear plateau formation cannot stabilize the waves, and growth occurs until the nonlinear mechanisms of ion resonance broadening and electron trapping provide saturation. The large amplitude and coherent nature of the resulting wave imply that quasi-linear theory provides only a lower limit to the ion heating. An upper bound on the heating rate is derived using a time-average model of ion dynamics in the coherent waves. The effects of ion heating in the presence of the magnetic gradient force and parallel electric fields are considered, with the result that perpendicular energies over 100 eV are easily attainable from a 1 eV source plasma. Perpendicular heating in the absence of a parallel electric field yields conical ion distributions, which in the presence of an electric field become field-aligned beams.

  8. Time-Fractional KdV Equation for the plasma in auroral zone using Variational Methods

    CERN Document Server

    El-Wakil, El-Said A; Elshewy, Emad K; Mahmoud, Aber A

    2010-01-01

    The reductive perturbation method has been employed to derive the Korteweg-de Vries (KdV) equation for small but finite amplitude electrostatic waves. The Lagrangian of the time fractional KdV equation is used in similar form to the Lagrangian of the regular KdV equation. The variation of the functional of this Lagrangian leads to the Euler-Lagrange equation that leads to the time fractional KdV equation. The Riemann-Liouvulle definition of the fractional derivative is used to describe the time fractional operator in the fractional KdV equation. The variational-iteration method given by He is used to solve the derived time fractional KdV equation. The calculations of the solution with initial condition A0*sech(cx)^2 are carried out. Numerical studies have been made using plasma parameters close to those values corresponding to the dayside auroral zone. The effects of the time fractional parameter on the electrostatic solitary structures are presented.

  9. Hint of star exoplanet interaction by modelling the stellar auroral radio emission of the M8.5 dwarf TVLM 513-46546

    CERN Document Server

    Leto, P; Buemi, C S; Umana, G; Ingallinera, A; Cerrigone, L

    2016-01-01

    The stellar auroral radio emission has been recognized in some early-type magnetic stars and in many ultra-cool dwarfs. The typical features are the highly polarized pulses explained in terms of Electron Cyclotron Maser emission mechanism. The A0 type star CU Virginis is the prototype of the stars showing this coherent emission; the repeatability and stability of its auroral radio emission allow us to well study this elusive phenomenon. Taking advantage of the CU Vir insights, we built a 3D-model able to reproduce the timing and pulse profile of the auroral radio emission from a dipolar magnetosphere. This model can be applied to stars with an overall symmetric magnetic field topology and showing auroral radio emission, like the ultra-cool dwarfs. In this paper, we simulate the cyclic circularly-polarized pulses of the ultra-cool dwarf TVLM 513-46546, observed with the VLA at 4.88 and 8.44 GHz on May 2006. The auroral radio emission originates in polar rings located at different elevations as a function of th...

  10. An interhemispheric comparison of GPS phase scintillation with auroral emission observed at the South Pole and from the DMSP satellite

    Directory of Open Access Journals (Sweden)

    Paul Prikryl

    2013-06-01

    Full Text Available The global positioning system (GPS phase scintillation caused by high-latitude ionospheric irregularities during an intense high-speed stream (HSS of the solar wind from April 29 to May 5, 2011, was observed using arrays of GPS ionospheric scintillation and total electron content monitors in the Arctic and Antarctica. The one-minute phase-scintillation index derived from the data sampled at 50 Hz was complemented by a proxy index (delta phase rate obtained from 1-Hz GPS data. The scintillation occurrence coincided with the aurora borealis and aurora australis observed by an all-sky imager at the South Pole, and by special sensor ultraviolet scanning imagers on board satellites of the Defense Meteorological Satellites Program. The South Pole (SP station is approximately conjugate with two Canadian High Arctic Ionospheric Network stations on Baffin Island, Canada, which provided the opportunity to study magnetic conjugacy of scintillation with support of riometers and magnetometers. The GPS ionospheric pierce points were mapped at their actual or conjugate locations, along with the auroral emission over the South Pole, assuming an altitude of 120 km. As the aurora brightened and/or drifted across the field of view of the all-sky imager, sequences of scintillation events were observed that indicated conjugate auroras as a locator of simultaneous or delayed bipolar scintillation events. In spite of the greater scintillation intensity in the auroral oval, where phase scintillation sometimes exceeded 1 radian during the auroral break-up and substorms, the percentage occurrence of moderate scintillation was highest in the cusp. Interhemispheric comparisons of bipolar scintillation maps show that the scintillation occurrence is significantly higher in the southern cusp and polar cap.

  11. Stellar wind-magnetosphere interaction at exoplanets: computations of auroral radio powers

    Science.gov (United States)

    Nichols, J. D.; Milan, S. E.

    2016-09-01

    We present calculations of the auroral radio powers expected from exoplanets with magnetospheres driven by an Earth-like magnetospheric interaction with the solar wind. Specifically, we compute the twin cell-vortical ionospheric flows, currents, and resulting radio powers resulting from a Dungey cycle process driven by dayside and nightside magnetic reconnection, as a function of planetary orbital distance and magnetic field strength. We include saturation of the magnetospheric convection, as observed at the terrestrial magnetosphere, and we present power-law approximations for the convection potentials, radio powers and spectral flux densities. We specifically consider a solar-age system and a young (1 Gyr) system. We show that the radio power increases with magnetic field strength for magnetospheres with saturated convection potential, and broadly decreases with increasing orbital distance. We show that the magnetospheric convection at hot Jupiters will be saturated, and thus unable to dissipate the full available incident Poynting flux, such that the magnetic Radiometric Bode's Law (RBL) presents a substantial overestimation of the radio powers for hot Jupiters. Our radio powers for hot Jupiters are ˜5-1300 TW for hot Jupiters with field strengths of 0.1-10 BJ orbiting a Sun-like star, while we find that competing effects yield essentially identical powers for hot Jupiters orbiting a young Sun-like star. However, in particular, for planets with weaker magnetic fields, our powers are higher at larger orbital distances than given by the RBL, and there are many configurations of planet that are expected to be detectable using SKA.

  12. On the collocation between dayside auroral activity and coherent HF radar backscatter

    Directory of Open Access Journals (Sweden)

    J. Moen

    Full Text Available The 2D morphology of coherent HF radar and optical cusp aurora has been studied for conditions of predominantly southward IMF conditions, which favours low-latitude boundary layer reconnection. Despite the variability in shape of radar cusp Doppler spectra, the spectral width criterion of > 220 m s–1 proves to be a robust cusp discriminator. For extended periods of well-developed radar backscatter echoes, the equatorward boundary of the > 220 m s–1 spectral width enhancement lines up remarkably well with the equatorward boundary of the optical cusp aurora. The spectral width boundary is however poorly determined during development and fading of radar cusp backscatter. Closer inspection of radar Doppler profile characteristics suggests that a combination of spectral width and shape may advance boundary layer identification by HF radar. For the two December days studied the onset of radar cusp backscatter occurred within pre-existing 630.0 nm cusp auroral activity and appear to be initiated by sunrise, i.e. favourable radio wave propagation conditions had to develop. Better methods are put forward for analysing optical data, and for physical interpretation of HF radar data, and for combining these data, as applied to detection, tracking, and better understanding of dayside aurora. The broader motivation of this work is to develop wider use by the scientific community, of results of these techniques, to accelerate understanding of dynamic high-latitude boundary-processes. The contributions in this work are: (1 improved techniques of analysis of observational data, yielding meaningfully enhanced accuracy for deduced cusp locations; (2 a correspondingly more pronounced validation of correlation of boundary locations derived from the observational data set; and (3 a firmer physical rationale as to why the good correlation observed should theoretically be expected.

    Key words: Ionosphere (ionospheric

  13. A new type of daytime high-frequency VLF emissions at auroral latitudes ("bird emissions")

    Science.gov (United States)

    Manninen, J.; Turunen, T.; Kleimenova, N. G.; Gromova, L. I.; Kozlovskii, A. E.

    2017-01-01

    This paper is concerned with a new, previously unknown type of high-frequency (above 4 kHz) VLF emissions that were detected during winter VLF campaigns in Kannuslehto ( L 5.5), Finland. These previously unknown emissions have been discovered as a result of the application of special digital filtering: it clears the VLF records from pulse signals of intensive atmospherics, which prevent other kinds of VLF emissions in the same frequency range from being seen on spectrograms. As it appears, aside from wellknown bursts of auroral hisses and discrete quasiperiodic emissions, a previously unknown type of daytime right-hand polarized VLF waves is also present at frequencies above 4 kHz. These emissions can persist for several hours as series of separate short discrete wideband (from 4 to 10 kHz and higher) signals, each with a duration between one and several minutes. It has been found that such signals can be observed almost daily in winter. These emissions sound like bird's chirping to a human ear; for that reason, they were called "bird emissions." The dynamic spectra of individual signals often resemble flying birds. The signals are observed during daytime, more often in magnetically quiet conditions preceded by geomagnetic disturbances. As a rule, the occurrence of these bird emissions is accompanied by a slight increase in electron density in the lower ionosphere, which is evidence of the precipitation of energetic (>30 keV) electrons. This raises a number of questions as to where and how the VLF bird emissions are generated and how such emissions, at frequencies greatly exceeding half the electron equatorial gyrofrequency at L 5.5, can reach the Earth's surface.

  14. Crowd-sourcing, Communicating, and Improving Auroral Science at the Speed of Social Media through Aurorasaurus.org

    Science.gov (United States)

    Patel, K.; MacDonald, E.; Case, N.; Hall, M.; Clayton, J.; Heavner, M.; Tapia, A.; Lalone, N.; McCloat, S.

    2015-12-01

    On March 17, 2015, a geomagnetic storm—the largest of the solar cycle to date— hit Earth and gave many sky watchers around the world a beautiful auroral display. People made thousands of aurora-related tweets and direct reports to Aurorasaurus.org, an interdisciplinary citizen science project that tracks auroras worldwide in real-time through social media and the project's apps and website. Through Aurorasaurus, researchers are converting these crowdsourced observations into valuable data points to help improve models of where aurora can be seen. In this presentation, we will highlight how the team communicates with the public during these global, sporadic events to help drive and retain participation for Aurorasaurus. We will highlight some of the co-produced scientific results and increased media interest following this event. Aurorasaurus uses mobile apps, blogging, and a volunteer scientist network to reach out to aurora enthusiasts to engage in the project. Real-time tweets are voted on by other users to verify their accuracy and are pinned on a map located on aurorasaurus.org to help show the instantaneous, global auroral visibility. Since the project launched in October 2014, hundreds of users have documented the two largest geomagnetic storms of this solar cycle. In some cases, like for the St. Patrick's Day storm, users even reported seeing aurora in areas different than aurora models suggested. Online analytics indicate these events drive users to our page and many also share images with various interest groups on social media. While citizen scientists provide observations, Aurorasaurus gives back by providing tools to help the public see and understand the aurora. When people verify auroral sightings in a specific area, the project sends out alerts to nearby users of possible auroral visibility. Aurorasaurus team members around the world also help the public understand the intricacies of space weather and aurora science through blog articles

  15. Ionospheric feedback effects on the quasi-stationary coupling between LLBL and postnoon/evening discrete auroral arcs

    Directory of Open Access Journals (Sweden)

    M. M. Echim

    2008-05-01

    Full Text Available We discuss a model for the quasi-stationary coupling between magnetospheric sheared flows in the dusk sector and discrete auroral arcs, previously analyzed for the case of a uniform height-integrated Pedersen conductivity (ΣP. Here we introduce an ionospheric feedback as the variation of ΣP with the energy flux of precipitating magnetospheric electrons (εem. One key-component of the model is the kinetic description of the interface between the duskward LLBL and the plasma sheet that gives the profile of Φm, the magnetospheric electrostatic potential. The velocity shear in the dusk LLBL plays the role of a generator for the auroral circuit closing through Pedersen currents in the auroral ionosphere. The field-aligned current density, j||, and the energy flux of precipitating electrons are given by analytic functions of the field-aligned potential drop, ΔΦ, derived from standard kinetic models of the adiabatic motion of particles. The ionospheric electrostatic potential, Φi (and implicitely ΔΦ is determined from the current continuity equation in the ionosphere. We obtain values of ΔΦ of the order of kilovolt and of j|| of the order of tens of μA/m2 in thin regions of the order of several kilometers at 200 km altitude. The spatial scale is significantly smaller and the peak values of ΔΦ, j|| and εem are higher than in the case of a uniform ΣP. Effects on the postnoon/evening auroral arc electrodynamics due to variations of dusk LLBL and solar wind dynamic and kinetic pressure are discussed. In thin regions (of the order of kilometer embedding the maximum of ΔΦ we evidence a non-linear regime of the current-voltage relationship. The model predicts also that visible arcs form when the velocity shear in LLBL is above a threshold value depending on the generator and

  16. Nonlinear coupling of lower hybrid waves to the kinetic low-frequency plasma response in the auroral ionosphere

    Science.gov (United States)

    Sanbonmatsu, K. Y.; Goldman, M. V.; Newman, D. L.

    A hybrid kinetic-fluid model is developed which is relevant to lower hybrid spikelets observed in the topside auroral ionosphere [Vago et al., 1992; Eriksson et al., 1994]. In contrast to previous fluid models [Shapiro et al., 1995; Tam and Chang, 1995; Seyler, 1994; Shapiro et al., 1993] our linear low frequency plasma response is magnetized and kinetic. Fluid theory is used to incorporate the nonlinear wave coupling. Performing a linear stability analysis, we calculate the growth rate for the modulational instability, driven by a lower hybrid wave pump. We find that both the magnetic and kinetic effects inhibit the modulational instability.

  17. A statistical study of the THEMIS satellite data for plasma sheet electrons carrying auroral upward field-aligned currents

    Science.gov (United States)

    Lee, S.; Shiokawa, K.; McFadden, J. P.

    2010-12-01

    The magnetospheric electron precipitation along the upward field-aligned currents without the potential difference causes diffuse aurora, and the magnetospheric electrons accelerated by a field-aligned potential difference cause the intense and bright type of aurora, namely discrete aurora. In this study, we are trying to find out when and where the aurora can be caused with or without electron acceleration. We statistically investigate electron density, temperature, thermal current, and conductivity in the plasma sheet using the data from the electrostatic analyzer (ESA) onboard the THEMIS-D satellite launched in 2007. According to Knight (Planet. Space Sci., 1973) and Lyons (JGR, 1980), the thermal current, jth(∝ nT^(1/2) where n is electron density and T is electron temperature in the plasma sheet), represents the upper limit to field aligned current that can be carried by magnetospheric electrons without field-aligned potential difference. The conductivity, K(∝ nT^(-1/2)), represents the efficiency of the upward field-aligned current (j) that the field-aligned potential difference (V) can produce (j=KV). Therefore, estimating jth and K in the plasma sheet is important in understanding the ability of plasma sheet electrons to carry the field-aligned current which is driven by various magnetospheric processes such as flow shear and azimuthal pressure gradient. Similar study was done by Shiokawa et al. (2000) based on the auroral electron data obtained by the DMSP satellites above the auroral oval and the AMPTE/IRM satellite in the near Earth plasma sheet at 10-18 Re on February-June 1985 and March-June 1986 during the solar minimum. The purpose of our study is to examine auroral electrons with pitch angle information inside 12 Re where Shiokawa et al. (2000) did not investigate well. For preliminary result, we found that in the dawn side inner magnetosphere (source of the region 2 current), electrons can make sufficient thermal current without field

  18. Letter to the EditorOn the use of the sunspot number for the estimation of past solar and upper atmosphere conditions from historical and modern auroral observations

    Directory of Open Access Journals (Sweden)

    J. M Vaquero

    2005-07-01

    Full Text Available In this short contribution the use of different sunspot numbers for the estimation of past solar and upper atmosphere conditions from historical and modern auroral observations realised by Schröder et al. (2004 is analysed. Moreover, some comments are made on the relationships between mean annual visual observations of the auroras at middle latitudes of Europe and the mean annual sunspot number during 1780–1829. Keywords. Atmospheric composition and structure (Airglow and aurora – Magnetospheric physics (Auroral phenomena, solar wind-magnetosphere interactions – History of geophysics (Solar-planetary relationship

  19. The location of the open-closed magnetic field line boundary in the dawn sector auroral ionosphere

    Directory of Open Access Journals (Sweden)

    J. A. Wild

    2004-11-01

    Full Text Available As a measure of the degree of coupling between the solar wind-magnetosphere-ionosphere systems, the rate at which the size of the polar cap (the region corresponding to ionospheric termini of open magnetic flux tubes varies is of prime importance. However, a reliable technique by which the extent of the polar cap might be routinely monitored has yet to be developed. Current techniques provide particularly ambiguous indications of the polar cap boundary in the dawn sector. We present a case study of space- and ground-based observations of the dawn-sector auroral zone and attempt to determine the location of the polar cap boundary using multi-wavelength observations of the ultraviolet aurora (made by the IMAGE FUV imager, precipitating particle measurements (recorded by the FAST, DMSP, and Cluster 1 and 3 satellites, and SuperDARN HF radar observations of the ionospheric Doppler spectral width boundary. We conclude that in the dawn sector, during the interval presented, neither the poleward edge of the wideband auroral UV emission (140-180nm nor the Doppler spectral width boundary were trustworthy indicators of the polar cap boundary location, while narrow band UV emissions in the range 130-140nm appear to be much more reliable.

  20. Auroral radio emission from late L and T dwarfs: A new constraint on dynamo theory in the substellar regime

    CERN Document Server

    Kao, Melodie M; Pineda, J Sebastian; Escala, Ivanna; Burgasser, Adam; Bourke, Stephen; Stevenson, David

    2015-01-01

    We have observed 6 late-L and T dwarfs with the Karl G. Jansky Very Large Array (VLA) to investigate the presence of highly circularly polarized radio emission, associated with large-scale auroral currents. Previous surveys encompassing ~60 L6 or later targets in this spectral range have yielded only one detection. Our sample includes the previously detected T6.5 dwarf 2MASS 10475385+2124234 as well as 5 new targets selected for the presence of H-alpha emission or optical/infrared photometric variability, which are possible manifestations of auroral activity. We detect 2MASS 10475385+2124234, as well as 4 of the 5 targets in our biased sample, including the strong IR variable SIMP J01365662+0933473 and bright H-alpha emitter 2MASS 12373919+6526148, reinforcing the possibility that activity at these disparate wavelengths is related. The radio emission frequency corresponds to a precise determination of the lower-bound magnetic field strength near the surface of each dwarf and this new sample provides robust co...

  1. Electrostatic solitary structures in presence of non-thermal electrons and a warm electron beam on the auroral field lines

    Energy Technology Data Exchange (ETDEWEB)

    Singh, S. V. [Indian Institute of Geomagnetism, Navi Mumbai (India); School of Physics, University of Kwazulu-Natal, Durban (South Africa); Lakhina, G. S. [Indian Institute of Geomagnetism, Navi Mumbai (India); Bharuthram, R. [University of the Western Cape, Bellville (South Africa); Pillay, S. R. [School of Physics, University of Kwazulu-Natal, Durban (South Africa)

    2011-12-15

    Electrostatic solitary waves (ESWs) have been observed by satellites in the auroral region of the Earth's magnetosphere. These ESWs are found to be having both positive and negative electrostatic potentials. Using the Sagdeeev psuedo-potential technique, arbitrary amplitude electron-acoustic solitary waves/double layers are studied in an unmagnetized plasma consisting of non-thermally distributed hot electrons, fluid cold electrons, a warm electron beam, and ions. The inertia of the warm electrons, and not the beam speed, is essential for the existence of positive potential solitary structures. Existence domains for positive as well as negative potential electrostatic solitons/double layers are obtained. For the typical auroral region parameters, the electric field amplitude of the negative potential solitons is found to be in the range {approx}(3-30) mV/m and {approx}(5-80) mV/m for the positive potential solitons. For the negative potential solitons/double layers, the amplitudes are higher when their widths are smaller. On the other hand, the amplitude of the positive potential structures increase with their widths.

  2. Auroral Radio Emission from Late L and T Dwarfs: A New Constraint on Dynamo Theory in the Substellar Regime

    Science.gov (United States)

    Kao, Melodie M.; Hallinan, Gregg; Pineda, J. Sebastian; Escala, Ivanna; Burgasser, Adam; Bourke, Stephen; Stevenson, David

    2016-02-01

    We have observed six late L and T dwarfs with the Karl G. Jansky Very Large Array (VLA) to investigate the presence of highly circularly polarized radio emission, associated with large-scale auroral currents. Previous surveys encompassing ∼60 L6 or later targets have yielded only one detection. Our sample includes the previously detected T6.5 dwarf 2MASS 10475385+2124234, as well as five new targets selected for the presence of Hα emission and/or optical infrared photometric variability, which are possible manifestations of auroral activity. We detect 2MASS 10475385+2124234, as well as four of the five targets in our biased sample, including the strong IR-variable source SIMP J01365662+0933473 and bright Hα emitter 2MASS 12373919+6526148, reinforcing the possibility that activity at these disparate wavelengths is related. The radio emission frequency corresponds to a precise determination of the lower-bound magnetic field strength near the surface of each dwarf, and this new sample provides robust constraints on dynamo theory in the low-mass brown dwarf regime. Magnetic fields ≳ 2.5 kG are confirmed for five of six targets. Our results provide tentative evidence that the dynamo operating in this mass regime may be inconsistent with predicted values from a recently proposed model. Further observations at higher radio frequencies are essential for verifying this assertion.

  3. Plasma flows, Birkeland currents and auroral forms in relation to the Svalgaard-Mansurov effect

    Directory of Open Access Journals (Sweden)

    P. E. Sandholt

    2012-05-01

    Full Text Available The traditional explanation of the polar cap magnetic deflections, referred to as the Svalgaard-Mansurov effect, is in terms of currents associated with ionospheric flow resulting from the release of magnetic tension on newly open magnetic field lines. In this study, we aim at an updated description of the sources of the Svalgaard-Mansurov effect based on recent observations of configurations of plasma flow channels, Birkeland current systems and aurorae in the magnetosphere-ionosphere system. Central to our description is the distinction between two different flow channels (FC 1 and FC 2 corresponding to two consecutive stages in the evolution of open field lines in Dungey cell convection, with FC 1 on newly open, and FC 2 on old open, field lines. Flow channel FC 1 is the result of ionospheric Pedersen current closure of Birkeland currents flowing along newly open field lines. During intervals of nonzero interplanetary magnetic field By component FC 1 is observed on either side of noon and it is accompanied by poleward moving auroral forms (PMAFs/prenoon and PMAFs/postnoon. In such cases the next convection stage, in the form of flow channel FC 2 on the periphery of the polar cap, is particularly important for establishing an IMF By-related convection asymmetry along the dawn-dusk meridian, which is a central element causing the Svalgaard-Mansurov effect. FC 2 flows are excited by the ionospheric Pedersen current closure of the northernmost pair of Birkeland currents in the four-sheet current system, which is coupled to the tail magnetopause and flank low-latitude boundary layer. This study is based on a review of recent statistical and event studies of central parameters relating to the magnetosphere-ionosphere current systems mentioned above. Temporal-spatial structure in the current systems is obtained by ground-satellite conjunction studies. On this point we emphasize the important information derived

  4. The dynamics and relationships of precipitation, temperature and convection boundaries in the dayside auroral ionosphere

    Directory of Open Access Journals (Sweden)

    J. Moen

    2004-06-01

    Full Text Available A continuous band of high ion temperature, which persisted for about 8h and zigzagged north-south across more than five degrees in latitude in the dayside (07:00-15:00MLT auroral ionosphere, was observed by the EISCAT VHF radar on 23 November 1999. Latitudinal gradients in the temperature of the F-region electron and ion gases (Te and Ti, respectively have been compared with concurrent observations of particle precipitation and field-perpendicular convection by DMSP satellites, in order to reveal a physical explanation for the persistent band of high Ti, and to test the potential role of Ti and Te gradients as possible markers for the open-closed field line boundary. The north/south movement of the equatorward Ti boundary was found to be consistent with the contraction/expansion of the polar cap due to an unbalanced dayside and nightside reconnection. Sporadic intensifications in Ti, recurring on ~10-min time scales, indicate that frictional heating was modulated by time-varying reconnection, and the band of high Ti was located on open flux. However, the equatorward Ti boundary was not found to be a close proxy of the open-closed boundary. The closest definable proxy of the open-closed boundary is the magnetosheath electron edge observed by DMSP. Although Te appears to be sensitive to magnetosheath electron fluxes, it is not found to be a suitable parameter for routine tracking of the open-closed boundary, as it involves case dependent analysis of the thermal balance. Finally, we have documented a region of newly-opened sunward convecting flux. This region is situated between the convection reversal boundary and the magnetosheath electron edge defining the open-closed boundary. This is consistent with a delay of several minutes between the arrival of the first (super-Alfvénic magnetosheath electrons and the response in the ionospheric

  5. Origin of type-2 thermal-ion upflows in the auroral ionosphere

    Directory of Open Access Journals (Sweden)

    L. M. Kagan

    2005-01-01

    Full Text Available The origin of thermal ion outflows exceeding 1km/s in the high-latitude F-region has been a subject of considerable debate. For cases with strong convection electric fields, the "evaporation" of the ions due to frictional heating below 400-500km has been shown to provide some satisfactory answers. By contrast, in the more frequent subclass of outflow events observed over auroral arcs, called type-2, there is no observational evidence for ion frictional heating. Instead, an electron temperature increase of up to 6000° K is observed over the outflow region. In this case, field-aligned electric fields have long been suspected to be involved, but this explanation did not seem to agree with expectations from the ion momentum balance. In the present work we provide a consistent scenario for the type-2 ion upflows based on our case study of an event that occurred on 20 February 1990. We introduce, for the first time, the electron energy balance in the analysis. We couple this equation with the ion momentum balance to study the salient features of the observations and conclude that type-2 ion outflows and the accompanying electron heating events are indeed consistent with the existence of a field-aligned electric field. However, for our explanation to work, we have to require that an allowance be made for electron scattering by high frequency turbulence. This turbulence could be generated at first by the very fast response of the electrons themselves to a newly imposed electric field that would be partly aligned with the geomagnetic field. The high frequencies of the waves would make it impossible for the ions to react to the waves. We have found the electron collision frequency associated with scattering from the waves to be rather modest, i.e. comparable to the ambient electron-ion collision frequency. The field-aligned electric field inferred from the observations is likewise of the same order of magnitude as the normal ambipolar field, at least for

  6. Visualizing Space Weather: The Planeterrella Auroral Simulator as a Heliophysics Public Outreach Tool

    Science.gov (United States)

    Masongsong, E. V.; Lilensten, J.; Booth, M. J.; Suri, G.; Heflinger, T. G.; Angelopoulos, V.

    2014-12-01

    The NASA THEMIS and ARTEMIS satellite missions study "space weather," which describes the solar wind influence on Earth's protective magnetic shield, the magnetosphere. Space weather is important to study and predict because it can damage critical GPS and communications satellites, harm space travelers, and even disable our global electrical grid. The Planeterrella is an innovative heliophysics outreach demonstration, expanding public awareness of space weather by visualizing the sun-Earth connection up close and in-person. Using a glass vacuum chamber, two magnetized spheres and a 1kV power supply, the device can simulate plasma configurations of the solar corona, solar wind, Van Allen radiation belts, and auroral ovals, all of which are observable only by satellites. This "aurora in a bottle" is a modernized version of the original Terrella built by Kristian Birkeland in the 1890s to show that the aurora are electrical in nature. Adapted from plans by Lilensten et al. at CNRS-IPAG, the UCLA Planeterrella was completed in Nov. 2013, the second device of its kind in the U.S., and the centerpiece of the THEMIS/ARTEMIS mobile public outreach exhibit. In combination with captivating posters, 3D magnetic field models, dazzling aurora videos and magnetosphere animations, the Planeterrella has already introduced over 1200 people to the electrical link between our sun and the planets. Most visitors had seen solar flare images in the news, however the Planeterrella experience enhanced their appreciation of the dynamic solar wind and its effects on Earth's invisible magnetic field. Most importantly, visitors young and old realized that magnets are not just cool toys or only for powering hybrid car motors and MRIs, they are a fundamental aspect of ongoing life on Earth and are key to the formation and evolution of planets, moons, and stars, extending far beyond our galaxy to other planetary systems throughout the universe. Novel visualizations such as the Planeterrella can

  7. Variation of Jupiter's aurora observed by Hisaki/EXCEED: 1. Observed characteristics of the auroral electron energies compared with observations performed using HST/STIS

    Science.gov (United States)

    Tao, Chihiro; Kimura, Tomoki; Badman, Sarah V.; Murakami, Go; Yoshioka, Kazuo; Tsuchiya, Fuminori; André, Nicolas; Yoshikawa, Ichiro; Yamazaki, Atsushi; Shiota, Daikou; Tadokoro, Hiroyasu; Fujimoto, Masaki

    2016-05-01

    Temporal variation of Jupiter's northern aurora is detected using the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) on board JAXA's Earth-orbiting planetary space telescope Hisaki. The wavelength coverage of EXCEED includes the H2 Lyman and Werner bands at 80-148 nm from the entire northern polar region. The prominent periodic modulation of the observed emission corresponds to the rotation of Jupiter's main auroral oval through the aperture, with additional superposed -50%-100% temporal variations. The hydrocarbon color ratio (CR) adopted for the wavelength range of EXCEED is defined as the ratio of the emission intensity in the long wavelength range of 138.5-144.8 nm to that in the short wavelength range of 126.3-130 nm. This CR varies with the planetary rotation phase. Short- (within one planetary rotation) and long-term (> one planetary rotation) enhancements of the auroral power are observed in both wavelength ranges and result in a small CR variation. The occurrence timing of the auroral power enhancement does not clearly depend on the central meridian longitude. Despite the limitations of the wavelength coverage and the large field of view of the observation, the auroral spectra and CR-brightness distribution measured using EXCEED are consistent with other observations.

  8. Auroral current systems in Saturn's magnetosphere: comparison of theoretical models with Cassini and HST observations

    Directory of Open Access Journals (Sweden)

    S. W. H. Cowley

    2008-09-01

    Full Text Available The first simultaneous observations of fields and plasmas in Saturn's high-latitude magnetosphere and UV images of the conjugate auroral oval were obtained by the Cassini spacecraft and the Hubble Space Telescope (HST in January 2007. These data have shown that the southern auroral oval near noon maps to the dayside cusp boundary between open and closed field lines, associated with a major layer of upward-directed field-aligned current (Bunce et al., 2008. The results thus support earlier theoretical discussion and quantitative modelling of magnetosphere-ionosphere coupling at Saturn (Cowley et al., 2004, that suggests the oval is produced by electron acceleration in the field-aligned current layer required by rotational flow shear between strongly sub-corotating flow on open field lines and near-corotating flow on closed field lines. Here we quantitatively compare these modelling results (the "CBO" model with the Cassini-HST data set. The comparison shows good qualitative agreement between model and data, the principal difference being that the model currents are too small by factors of about five, as determined from the magnetic perturbations observed by Cassini. This is suggested to be principally indicative of a more highly conducting summer southern ionosphere than was assumed in the CBO model. A revised model is therefore proposed in which the height-integrated ionospheric Pedersen conductivity is increased by a factor of four from 1 to 4 mho, together with more minor adjustments to the co-latitude of the boundary, the flow shear across it, the width of the current layer, and the properties of the source electrons. It is shown that the revised model agrees well with the combined Cassini-HST data, requiring downward acceleration of outer magnetosphere electrons through a ~10 kV potential in the current layer at the open-closed field line boundary to produce an auroral oval of ~1° width with UV emission intensities of a few tens of kR.

  9. Physical and Chemical Properties of Jupiter's Polar Vortices and Regions of Auroral Influence Revealed Through High-Resolution Infrared Imaging

    Science.gov (United States)

    Fernandes, Josh; Orton, Glenn S.; Sinclair, James; Kasaba, Yasumasa; Sato, Takao M.; Fujiyoshi, Takuya; Momary, Thomas W.; Yanamandra-Fisher, Padma A.

    2016-10-01

    We report characterization of the physical and chemical properties of Jupiter's polar regions derived from mid-infrared imaging of Jupiter covering all longitudes at unprecedented spatial resolution using the COMICS instrument at the Subaru Telescope on the nights of January 24 and 25, 2016 (UT). Because of Jupiter's slight axial tilt of 3°, the low angular resolution and incomplete longitudinal coverage of previous mid-infrared observations, the physical and chemical properties of Jupiter's polar regions have been poorly characterized. In advance of the Juno mission's exploration of the polar regions, this study focuses on mapping the 3-dimensional structure of Jupiter's polar regions, specifically to characterize the polar vortices and compact regions of auroral influence. Using mid-infrared images taken in the 7.8 - 24.2 µm range, we determined the 3-dimensional temperature field, mapped the para-H2 fraction and aerosol opacity at 700 mbar and lower pressures, and constrained the distribution of gaseous NH3 in Jupiter's northern and southern polar regions. Retrievals of these atmospheric parameters was performed using NEMESIS, a radiative transfer forward model and retrieval code. Preliminary results indicate that there are vortices at both poles, each with very distinct low-latitude boundaries approximately 60° (planetocentric) from the equator, which can be defined by sharp thermal gradients extending at least from the upper troposphere (500 mbar) and into the stratosphere (0.1 mbar). These polar regions are characterized by lower temperatures, lower aerosol number densities, and lower NH3 volume mixing ratios, compared with the regions immediately outside the vortex boundaries. These images also provided the highest resolution of prominent auroral-related stratospheric heating to date, revealing a teardrop-shaped morphology in the north and a sharp-edged oval shape in the south. Both appear to be contained inside the locus of H3+ auroral emission detected

  10. On the lifetime and extent of an auroral westward flow channel (AWFC observed during a magnetospheric substorm

    Directory of Open Access Journals (Sweden)

    M. L. Parkinson

    Full Text Available A -190-nT negative bay in the geomagnetic X component measured at Macquarie Island ( -65° L showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27 February 2000. Signatures of an auroral westward flow channel (AWFC were observed nearly simultaneously in the backscatter power, LOS Doppler velocity, and Doppler spectral width measured using the Tasman International Geospace Environment Radar (TIGER, a Southern Hemisphere HF SuperDARN radar. Many of the characteristics of the AWFC were similar to those occurring during a polarisation jet (PJ, or subauroral ion drift (SAID event, and suggest that it may have been a pre-cursor to a fully developed, intense westward flow channel satisfying all of the criteria defining a PJ/SAID. A beam-swinging analysis showed that the westward drifts (poleward electric field associated with the flow channel were very structured in time and space, but the smoothed velocities grew to ~ 800 ms-1 (47 mVm-1 during the 22-min substorm onset interval 09:56 to 10:18 UT. Maximum west-ward drifts of >1.3 km s-1 (>77 mVm-1 occurred during a ~ 5-min velocity spike, peaking at 10:40 UT during the expansion phase. The drifts decayed rapidly to ~ 300 ms-1 (18 mVm-1 during the 6-min recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of 74 min, and was located near -65° L in the evening sector west of the Harang discontinuity. The large westward drifts were confined to a geographic zonal channel of longitudinal ex-tent >20° (>1.3 h magnetic local time, and latitudinal width ~2° L. Using a half-width of ~ 100 km in latitude, the peak electric potential was >7.7 kV. However, a transient velocity of >3.1 km s-1 with potential >18.4 kV was observed further poleward at the end of the recovery phase. Auroral oval boundaries determined

  11. Intensification of dayside diffuse auroral precipitation: contribution of dayside Whistler-mode chorus waves in realistic magnetic fields

    Directory of Open Access Journals (Sweden)

    R. Shi

    2012-09-01

    Full Text Available Compared to the recently improved understanding of nightside diffuse aurora, the mechanism(s responsible for dayside diffuse aurora remains poorly understood. While dayside chorus has been thought as a potential major contributor to dayside diffuse auroral precipitation, quantitative analyses of the role of chorus wave scattering have not been carefully performed. In this study we investigate a dayside diffuse auroral intensification event observed by the Chinese Arctic Yellow River Station (YRS all-sky imagers (ASI on 7 January 2005 and capture a substantial increase in diffuse auroral intensity at the 557.7 nm wavelength that occurred over almost the entire ASI field-of-view near 09:24 UT, i.e., ~12:24 MLT. Computation of bounce-averaged resonant scattering rates by dayside chorus emissions using realistic magnetic field models demonstrates that dayside chorus scattering can produce intense precipitation losses of plasma sheet electrons on timescales of hours (even approaching the strong diffusion limit over a broad range of both energy and pitch angle, specifically, from ~1 keV to 50 keV with equatorial pitch angles from the loss cone to up to ~85° depending on electron energy. Subsequent estimate of loss cone filling index indicates that the loss cone can be substantially filled, due to dayside chorus driven pitch angle scattering, at a rate of ≥0.8 for electrons from ~500 eV to 50 keV that exactly covers the precipitating electrons for the excitation of green-line diffuse aurora. Estimate of electron precipitation flux at different energy levels, based on loss cone filling index profile and typical dayside electron distribution observed by THEMIS spacecraft under similar conditions, gives a total precipitation electron energy flux of the order of 0.1 erg cm−2 s−1 with ~1 keV characteristic energy (especially when using T01s, which can be very likely to cause intense green-line diffuse aurora activity on the

  12. Measuring the seeds of ion outflow: Auroral sounding rocket observations of low-altitude ion heating and circulation

    Science.gov (United States)

    Fernandes, P. A.; Lynch, K. A.; Zettergren, M.; Hampton, D. L.; Bekkeng, T. A.; Cohen, I. J.; Conde, M.; Fisher, L. E.; Horak, P.; Lessard, M. R.; Miceli, R. J.; Michell, R. G.; Moen, J.; Powell, S. P.

    2016-02-01

    We present an analysis of in situ measurements from the MICA (Magnetosphere-Ionosphere Coupling in the Alfvén Resonator) nightside auroral sounding rocket with comparisons to a multifluid ionospheric model. MICA made observations at altitudes below 325 km of the thermal ion kinetic particle distributions that are the origins of ion outflow. Late flight, in the vicinity of an auroral arc, we observe frictional processes controlling the ion temperature. Upflow of these cold ions is attributed to either the ambipolar field resulting from the heated electrons or possibly to ion-neutral collisions. We measure E→×B→ convection away from the arc (poleward) and downflows of hundreds of m s-1 poleward of this arc, indicating small-scale low-altitude plasma circulation. In the early flight we observe DC electromagnetic Poynting flux and associated ELF wave activity influencing the thermal ion temperature in regions of Alfvénic aurora. We observe enhanced, anisotropic ion temperatures which we conjecture are caused by transverse heating by wave-particle interactions (WPI) even at these low altitudes. Throughout this region we observe several hundred m s-1 upflow of the bulk thermal ions colocated with WPI; however, the mirror force is negligible at these low energies; thus, the upflow is attributed to ambipolar fields (or possibly neutral upwelling drivers). The low-altitude MICA observations serve to inform future ionospheric modeling and simulations of (a) the need to consider the effects of heating by WPI at altitudes lower than previously considered viable and (b) the occurrence of structured and localized upflows/downflows below where higher-altitude heating rocesses are expected.

  13. X-ray Probes of Magnetospheric Interactions with Jupiter's Auroral zones, the Galilean Satellites, and the Io Plasma Torus

    Science.gov (United States)

    Elsner, R. F.; Ramsey, B. D.; Waite, J. H., Jr.; Rehak, P.; Johnson, R. E.; Cooper, J. F.; Swartz, D. A.

    2004-01-01

    Remote observations with the Chandra X-ray Observatory and the XMM-Newton Observatory have shown that the Jovian system is a source of x-rays with a rich and complicated structure. The planet's polar auroral zones and its disk are powerful sources of x-ray emission. Chandra observations revealed x-ray emission from the Io Plasma Torus and from the Galilean moons Io, Europa, and possibly Ganymede. The emission from these moons is certainly due to bombardment of their surfaces of highly energetic protons, oxygen and sulfur ions from the region near the Torus exciting atoms in their surfaces and leading to fluorescent x-ray emission lines. Although the x-ray emission from the Galilean moons is faint when observed fiom Earth orbit, an imaging x-ray spectrometer in orbit around these moons, operating at 200 eV and above with 150 eV energy resolution, would provide a detailed mapping (down to 40 m spatial resolution) of the elemental composition in their surfaces. Here we describe the physical processes leading to x-ray emission fiom the surfaces of Jupiter's moons and the instrumental properties, as well as energetic ion flux models or measurements, required to map the elemental composition of their surfaces. We discuss the proposed scenarios leading to possible surface compositions. For Europa, the two most extreme are (1) a patina produced by exogenic processes such as meteoroid bombardment and ion implantation, and (2) upwelling of material fiom the subsurface ocean. We also describe the characteristics of X - m , an imaging x-ray spectrometer under going a feasibility study for the JIM0 mission, with the ultimate goal of providing unprecedented x-ray studies of the elemental composition of the surfaces of Jupiter's icy moons and Io, as well as of Jupiter's auroral x-ray emission.

  14. The aurora as a source of planetary-scale waves in the middle atmosphere. [atmospheric turbulence caused by auroral energy absorption

    Science.gov (United States)

    Chiu, Y. T.; Straus, J. M.

    1974-01-01

    Photographs of global scale auroral forms taken by scanning radiometers onboard weather satellites in 1972 show that auroral bands exhibit well organized wave motion with typical zonal wave number of 5 or so. The scale size of these waves is in agreement with that of well organized neutral wind fields in the 150- to 200-km region during the geomagnetic storm of May 27, 1967. Further, the horizontal scale size revealed by these observations are in agreement with that of high altitude traveling ionospheric disturbances. It is conjectured that the geomagnetic storm is a source of planetary and synoptic scale neutral atmospheric waves in the middle atmosphere. Although there is, at present, no observation of substorm related waves of this scale size at mesospheric and stratospheric altitudes, the possible existence of a new source of waves of the proper scale size to trigger instabilities in middle atmospheric circulation systems may be significant in the study of lower atmospheric response to geomagnetic activity.

  15. Focused electrojetting for nanoscale 3-D fabrication

    Science.gov (United States)

    Lee, Minhee; Kim, Ho-Young

    2012-11-01

    Although extreme miniaturization of components in integrated circuits and biochemical chips has driven the development of various nanofabrication technologies, three-dimensional fabrication of nanoscale objects is still in its infancy. Here we propose a novel method to fabricate a free-standing nanowall by the line-by-line deposition of electrospun polymer nanofibers. We show that the electrified nanojet, which tends to get unstable as traveling in free space due to the Coulombic repulsion, can be stably focused onto a narrow line of metal electrode. On the conducting line, the polymer nanojet is spontaneously folded successively to form a wall-like structure. We rationalize the period of spontaneous folding by balancing the tension in the polymer fiber with the electrostatic interaction of the fiber with the metal ground. This novel fabrication scheme can be applied for the development of three-dimensional bioscaffolds, nanofilters and nanorobots.

  16. External production and control of electrojet irregularities.

    Science.gov (United States)

    Lee, K.; Kaw, P. K.; Kennel, C. F.

    1972-01-01

    Analytical investigation of parametric coupling of a large-amplitude 'pump' wave to a natural plasma mode of the ionospheric E layer. It is shown that the E layer plasma mode can be either stabilized or destabilized by the parametric process. Two necessary conditions for parametric interaction are (1) near frequency matching (i.e., the pump wave frequency should be near the local upper hybrid frequency) and (2) a finite electric field component of the pump wave perpendicular to the background static magnetic field. An investigation of the propagation characteristics of the pump wave in the magnetic equatorial region indicates that an obliquely propagating O mode in the magnetic meridian plane meets the two necessary conditions in an optimal manner. From typical values of ionospheric parameters it is estimated that the required incident energy flux of the pump wave for parametric stabilization or destabilization of the E layer plasma mode (near its natural marginal stability) is much less than 1 mW/sq m. Thus parametric coupling experiments for the ionospheric E layer are technically feasible.

  17. Plasma structure within poleward-moving cusp/cleft auroral transients: EISCAT Svalbard radar observations and an explanation in terms of large local time extent of events

    Directory of Open Access Journals (Sweden)

    M. Lockwood

    Full Text Available We report high-resolution observations of the southward-IMF cusp/cleft ionosphere made on December 16th 1998 by the EISCAT (European incoherent scatter Svalbard radar (ESR, and compare them with observations of dayside auroral luminosity, as seen at a wavelength of 630 nm by a meridian scanning photometer at Ny Ålesund, and of plasma flows, as seen by the CUTLASS (co-operative UK twin location auroral sounding system Finland HF radar. The optical data reveal a series of poleward-moving transient red-line (630 nm enhancements, events that have been associated with bursts in the rate of magnetopause reconnection generating new open flux. The combined observations at this time have strong similarities to predictions of the effects of soft electron precipitation modulated by pulsed reconnection, as made by Davis and Lockwood (1996; however, the effects of rapid zonal flow in the ionosphere, caused by the magnetic curvature force on the newly opened field lines, are found to be a significant additional factor. In particular, it is shown how enhanced plasma loss rates induced by the rapid convection can explain two outstanding anomalies of the 630 nm transients, namely how minima in luminosity form between the poleward-moving events and how events can re-brighten as they move poleward. The observations show how cusp/cleft aurora and transient poleward-moving auroral forms appear in the ESR data and the conditions which cause enhanced 630 nm emission in the transients: they are an important first step in enabling the ESR to identify these features away from the winter solstice when supporting auroral observations are not available.

    Key words: Ionosphere (polar ionosphere - Magnetospheric physics (magnetopause; cusp and boundary layers; solar wind-magnetosphere interactions

  18. Ion temperature anisotropy effects on threshold conditions of a shear-modified current driven electrostatic ion-acoustic instability in the topside auroral ionosphere

    OpenAIRE

    Perron, P. J. G.; J.-M. A. Noël; Kabin, K.; St-Maurice, J.-P.

    2013-01-01

    Temperature anisotropies may be encountered in space plasmas when there is a preferred direction, for instance, a strong magnetic or electric field. In this paper, we study how ion temperature anisotropy can affect the threshold conditions of a shear-modified current driven electrostatic ion-acoustic (CDEIA) instability. In particular, this communication focuses on instabilities in the context of topside auroral F-region situations and in the limit where finite Larmor radius...

  19. Formation and Identification of Counter Electrojet (CEJ) 1. Department of Physics and Astronomy, University of Nigeria, Nsukka, Nigeria. 2. Centre for Basic Space Science, University of Nigeria, Nsukka, Nigeria. 3. Department of Physics, University of Agriculture, Makurdi, Nigeria 1.Corresponding Author: franciscaokeke@yahoo.com OR francisca.okeke@unn.edu.ng

    Science.gov (United States)

    Okeke, F. N.; Okoro, E. C.; Isikwue, B. C.; Hanson, E.

    2012-12-01

    This study investigates the possible occurrence of counter equatorial electrojet (CEJ) and a quicker method for identification of CEJ. Data from a chain of magnetic observatories of World Data Center for Geomagnetism in Tokyo, Japan, was employed. It is strikingly interesting to observe that most CEJ occurred from morning through nighttime, with almost the same pattern of dHin depression. In Ascension Island [ASC], Huancayo [HUA] and Pondicherry [PND], most changes in horizontal component were found to be less than zero, which reveals an indication of full CEJ. Partial CEJ occurrences were observed during some hours at these stations where changes in horizontal component were found to be greater than zero. It is suggested that IMF turning north indicates CEJ, hence storm effects could also be attributed to CEJ existence. Some of our new findings are at variance with results of some previous workers; hence further work is suggested for further clarification. A quick method of easy identification of CEJ is suggested.

  20. Detailed dayside auroral morphology as a function of local time for southeast IMF orientation: implications for solar wind-magnetosphere coupling

    Directory of Open Access Journals (Sweden)

    P. E. Sandholt

    2004-11-01

    Full Text Available In two case studies we elaborate on spatial and temporal structures of the dayside aurora within 08:00-16:00 magnetic local time (MLT and discuss the relationship of this structure to solar wind-magnetosphere interconnection topology and the different stages of evolution of open field lines in the Dungey convection cycle. The detailed 2-D auroral morphology is obtained from continuous ground observations at Ny Ålesund (76° magnetic latitude (MLAT, Svalbard during two days when the interplanetary magnetic field (IMF is directed southeast (By>0; Bz<0. The auroral activity consists of the successive activations of the following forms: (i latitudinally separated, sunward moving, arcs/bands of dayside boundary plasma sheet (BPS origin, in the prenoon (08:00-11:00 MLT and postnoon (12:00-16:00 MLT sectors, within 70-75° MLAT, (ii poleward moving auroral forms (PMAFs emanating from the pre- and postnoon brightening events, and (iii a specific activity appearing in the 07:00-10:00 MLT/75-80° MLAT during the prevailing IMF By>0 conditions. The pre- and postnoon activations are separated by a region of strongly attenuated auroral activity/intensity within the 11:00-12:00 MLT sector, often referred to as the midday gap aurora. The latter aurora is attributed to the presence of component reconnection at the subsolar magnetopause where the stagnant magnetosheath flow lead to field-aligned currents (FACs which are of only moderate intensity. The much more active and intense aurorae in the prenoon (07:00-11:00 MLT and postnoon (12:00-16:00 MLT sectors originate in magnetopause reconnection events that are initiated well away from the subsolar point. The high-latitude auroral activity in the prenoon sector (feature iii is found to be accompanied by a convection channel at the polar cap boundary. The associated ground magnetic deflection (DPY is a Svalgaard-Mansurov effect. The convection channel is

  1. MITHRAS studies of the auroral oval and polar cap. Final report, 1 May 87-31 Dec 90

    Energy Technology Data Exchange (ETDEWEB)

    De la Beaujardiere, O.; Watermann, J.; Johnson, R.M.

    1991-01-01

    MITHRAS is a program of coordinated experiments dedicated to studying the coupling between the magnetosphere, the ionosphere, and the thermosphere. MITHRAS observations mostly involve the Sondrestrom radar in Greenland, but other incoherent scatter radars around the world were also used. Contract highlights include: (1) The most extensive comparisons ever made between incoherent scatter radar data and numerical simulation models were performed. These comparisons were based on both individual case studies and averaged data, and included observations from all the incoherent scatter radars. The comparisons showed general agreement between observations and model calculations but they also showed significant differences. (2) During solar-maximum conditions, the contribution to the height integrated Pederson conductivity from solar-produced F-region ionization can be as large as 60% of the total. (3) Under certain geophysical conditions it appears possible to identify the low-altitude cusp and distinguish it from the cleft. The cusp proper appears to be characterized by enhanced F region plasma density collocated with elevated F region electron temperature; it does not appear to be associated with a particular plasma flow pattern signature. (4) A new mechanism was proposed to explain how auroral surges might be formed. It was suggested that the surge was associated with a distortion of the poleward boundary of the aurora, and that this distortion was caused by the field aligned currents within the head of the surge.

  2. Observations of a gradual transition between Ps 6 activity with auroral torches and surgelike pulsations during strong geomagnetic disturbances

    Energy Technology Data Exchange (ETDEWEB)

    Steen, A.; Collis, P.N.; Evans, D.; Kremser, G.; Capelle, S.; Rees, D.; Tsurutani, B.T.

    1988-08-01

    A long-lasting large-amplitude pulsation event was observed on January 10, 1983, 0200--0600 UT (0411--0745 MLT) in the ionosphere and in the magnetosphere. In the ionosphere the characteristics of the pulsations changed from being Ps 6/auroral torches toward substorms and back to Ps 6 over the 4-hour period. At the geostationary orbit (6.6 Re) the corresponding characteristics were a modulation of the high-energy (greater than or equal to20 keV) particle intensity and plasma dropouts. Following the work by Rostoker and Samson (1984), we propose an interpretation of the event in which the pulsations are caused by the Kelvin-Helmholtz instability, during an interval of strong magnetospheric convection. The gradual transition between Ps 6 pulsations and substorm structures is interpreted as being different results of the Kelvin-Helmholtz instability, caused by different states of the magnetospheric convection. The proposed explanation forms the basis for a discussion on a simplified scheme of the substorm sequence. copyright American Geophysical Union 1988

  3. A Simulation Study of Ionization Depletion in the Auroral Ionospheric F-Region Caused by Strong Convection Electric Field

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The effects of strong convection electric field on the electron density in the auroral ionospheric F region have been simulated numerically by means of a physical model. It is found that an enhancement of electric field directed west-northward in post-noon or west-southward in pre-noon results in an ionization de pletion with its maximum at altitudes 40-50 km higher than that of the F2 peak. When the enhanced electric field lasts for 45 min and has a maximum about 32 mV/m, the resulted ionization depletions reach their max imum at the time just ~ 10 min behind the time when the convection electric field and ion temperature en hancements reach their maximum. This is consistent well with EISCAT observations. The magnitudes of thepercentage ionization depletions and their recovery time are dependent not only on the intensity of the electric field, but also on the diurnal variation phase of the background electron density.

  4. Effect of upflowing field-aligned electron beams on the electron cyclotron waves in the auroral magnetosphere

    Indian Academy of Sciences (India)

    Sushil Kumar; S K Singh; A K Gwal

    2007-04-01

    The role of low density upflowing field-aligned electron beams (FEBs) on the growth rate of the electron cyclotron waves at the frequencies r < ­e, propagating downward in the direction of the Earth's magnetic field, has been analysed in the auroral region at e/e < 1 where e is the plasma frequency and ­e is the gyrofrequency. The FEBs with low to high energy (b) but with low temperature (∥b) have no effect on these waves. The FEBs with b < 1 keV and ∥b (> 1.5 keV) have been found to have significant effect on the growth rate. Analysis has revealed that it is mainly the ∥b which inhibits the growth rate (magnitude) and the range of frequency (bandwidth) of the instability mainly in the higher frequency spectrum. The inhibition in the growth rate and bandwidth increases with increase in ∥b. The FEBs with less b (giving drift velocity) reduce growth rate more than the beams with larger b. The inhibition of growth rate increases with the increase in the ratio e/e indicating that the beams are more effective at higher altitudes.

  5. Introduction to the special issue on history development of solar terrestrial sciences including auroral sub-storms

    Science.gov (United States)

    Balan, N.; Parks, G.; Svalgaard, L.; Kamide, Y.; Lui, T.

    2016-12-01

    Solar terrestrial (ST) sciences started centuries ago and branched into different disciplines. Starting with naked eye to highly sophisticated novel experimental techniques, observations have revealed the secrets of the Sun, heliosphere, magnetosphere, plasmasphere, and ionosphere-atmosphere components of the ST system. Theories and theoretical models have been developed for the different components independently and together. World-wide efforts under different umbrella are being persuaded to understand the challenges of the ST system. The onset problem and role of O+ ions in sub-storm physics are two issues that are hotly debated. The onset problem is whether sub-storm is triggered by magnetic reconnection in the tail region at 15-20 Re or by a current disruption at ~12 Re. The issue on O+ role is whether O+ ions affect the dynamics of sub-storms under magnetic storm and non-storm conditions differently. This special issue of Geoscience Letters contains a collection of 15 papers on the history and development of solar terrestrial sciences including auroral sub-storms. Over half of the papers are based on the presentations in a session on the same topic organized at the AOGS (Asia Oceania geosciences Society) General Assembly held in Singapore during 02-07 August 2015. The rest of the papers from outside the assembly also falls within the theme of the special issue. The papers are organized in the order of history and development of ST coupling, sub-storms, and outer heliosphere.

  6. D- and E-region effects in the auroral zone during a moderately active 24-h period in July 2005

    Directory of Open Access Journals (Sweden)

    J. K. Hargreaves

    2007-08-01

    Full Text Available The effects of energetic electron precipitation into the auroral region at a time of enhanced solar wind have been investigated during a continuous period of 24 h, using the European Incoherent Scatter (EISCAT radar, an imaging riometer, and particle measurements on an orbiting satellite. The relative effects in the E region (120 km and D region (90 km are found to vary during the day, consistent with a gradual hardening of the incoming electron spectrum from pre-midnight to morning. Whereas the night spectra are single peaked, the daytime spectra are found to be double peaked, suggesting the presence of two distinct populations.

    A comparison between the radiowave absorption observed with the riometer and values estimated from the radar data shows generally good agreement, but with some discrepancies suggesting the occurrence of some small-scale features. The height and thickness of the absorbing region are estimated. Two periods of enhanced precipitation and the related radio absorption, one near magnetic midnight and one in the early morning, are studied in detail, including their horizontal structure and movement of the absorption patches.

    A sharp reduction of electron flux recorded on a POES satellite is related to the edge of an absorption region delineated by the imaging riometer. The observed particle flux is compared with a value deduced from the radar data during the overpass, and found to be in general agreement.

  7. Eastward-expanding auroral surges observed in the post-midnight sector during a multiple-onset substorm

    CERN Document Server

    Tanaka, Yoshimasa; Kadokura, Akira; Partamies, Noora; Whiter, Daniel; Enell, Carl-Fredrik; Brändström, Urban; Sergienko, Tima; Gustavsson, Björn; Kozlovsky, Alexander; Miyaoka, Hiroshi; Yoshikawa, Akimasa

    2016-01-01

    We present three eastward-expanding auroral surge (EEAS) events that were observed intermittently at intervals of about 15 min in the post-midnight sector (01:55-02:40 MLT) by all-sky imagers and magnetometers in northern Europe. It was deduced that each surge occurred just after each onset of a multiple-onset substorm, which was small-scale and did not clearly expand westward, because they were observed almost simultaneously with Pi 2 pulsations at the magnetic equator and magnetic bay variations at middle-to-high latitudes associated with the DP-1 current system. The EEASs showed similar properties to omega bands or torches reported in previous studies, such as recurrence intervals of about 15 min, concurrence with magnetic pulsations with amplitudes of several tens of nanotesla, horizontal scales of 300-400 km, and occurrence of a pulsating aurora in a diffuse aurora after the passage of the EEASs. Furthermore, the EEASs showed similar temporal evolution to the omega bands, during which eastward-propagatin...

  8. Simulations of resonant Alfvén waves generated by artificial HF heating of the auroral ionosphere

    Directory of Open Access Journals (Sweden)

    D. Pokhotelov

    2004-09-01

    Full Text Available Numerical two-dimensional two-fluid MHD simulations of dynamic magnetosphere-ionosphere (MI coupling have been performed to model the effects imposed on the auroral ionosphere by a powerful HF radio wave transmitter. The simulations demonstrate that modifications of the ionospheric plasma temperature and recombination due to artificial heating may trigger the ionospheric feedback instability when the coupled MI system is close to the state of marginal stability. The linear dispersion analysis of MI coupling has been performed to find the favorable conditions for marginal stability of the system. The development of the ionospheric feedback instability leads to the generation of shear waves which resonate in the magnetosphere between the heated ionospheric E-region and the strong gradient in the speed at altitudes of 1-2 RE. The application of the numerical results for the explanation of observations performed by low-orbiting satellites above the high-latitude ionosphere heated with a high power ground-based HF transmitter is discussed.

  9. Radar detection of a localized 1.4 Hz pulsation in auroral plasma, simultaneous with pulsating optical emissions, during a substorm

    Directory of Open Access Journals (Sweden)

    R. Cosgrove

    2010-10-01

    Full Text Available Many pulsating phenomena are associated with the auroral substorm. It has been considered that some of these phenomena involve kilometer-scale Alfvén waves coupling the magnetosphere and ionosphere. Electric field oscillations at the altitude of the ionosphere are a signature of such wave activity that could distinguish it from other sources of auroral particle precipitation, which may be simply tracers of magnetospheric activity. Therefore, a ground based diagnostic of kilometer-scale oscillating electric fields would be a valuable tool in the study of pulsations and the auroral substorm. In this study we attempt to develop such a tool in the Poker Flat incoherent scatter radar (PFISR. The central result is a statistically significant detection of a 1.4 Hz electric field oscillation associated with a similar oscillating optical emission, during the recovery phase of a substorm. The optical emissions also contain a bright, lower frequency (0.2 Hz pulsation that does not show up in the radar backscatter. The fact that higher frequency oscillations are detected by the radar, whereas the bright, lower frequency optical pulsation is not detected by the radar, serves to strengthen a theoretical argument that the radar is sensitive to oscillating electric fields, but not to oscillating particle precipitation. Although it is difficult to make conclusions as to the physical mechanism, we do not find evidence for a plane-wave-like Alfvén wave; the detected structure is evident in only two of five adjacent beams. We emphasize that this is a new application for ISR, and that corroborating results are needed.

  10. Characteristics of field-aligned density depletion irregularities in the auroral ionosphere that duct Z- and X-mode waves

    Science.gov (United States)

    James, H. G.

    2006-09-01

    The small-scale and two-point nature of the Observations of Electric-field Distributions in the Ionospheric Plasma—A Unique Strategy C (OEDIPUS-C, OC) dual-payload propagation experiment in the auroral ionosphere in 1995 has permitted improved measurements of the parameters of magnetic field-aligned density irregularities. Comparatively strong and dispersed pulses were observed at frequencies f just above the electron plasma frequency fp when the electron gyrofrequency fc was less than fp. The waves are interpreted as quasielectrostatic Z-mode propagation with dispersion surfaces close to those of the Langmuir solutions in wave vector space, albeit at somewhat lower refractive indices of about 50. If mission length surveys of the Z-wave intensities are aligned with histories of fp at the payload and of the strength of X- and fast Z-mode ionospheric reflection echoes, a strong positive correlation is found at momentary relative depletions of the ambient density. These observations are taken as evidence of ducting in the field-aligned depletions. The spectra of these strong Z-mode transmissions are similar to those of slow Z ducted spectra observed at similar f, fp, and fc values in the OEDIPUS-A experiment in 1989. The magnitudes of the density depletions are found to lie in the range 7-21% and to have cross-field dimensions of a few kilometers. The present duct dimensions are of the same order as the previous findings from ionospheric X-mode electromagnetic echoes on OC, but the depletions are up to 10 times deeper. Measurements of ducting irregularities can lead to insights into their formation. This will be important for our understanding of the interfaces of the ionospheric or magnetospheric topologies where irregularity formation is an important link in the large-scale flow of energy.

  11. Particle Signatures Observed by Geotail at 9-30 Re and Mapping of Auroral Regions to the Magnetosphere Without Field-Line Models

    Science.gov (United States)

    Shirai, H.; Hori, T.; Mukai, T.

    2004-12-01

    The Geotail spacecraft has often observed a rapid change of particle signatures at a geocentric distance around 10-15 Re. As the spacecraft approached the near-Earth region, particle spectra showing a low temperature, a small particle flux, and a large fluctuation in the magnetotail changed to those with a high temperature, a large flux, and a small fluctuation in the near-Earth region. This change often occurred rapidly as if there was a sharp boundary between the tail plasma sheet and the near-Earth plasma sheet. In the present paper, we call this boundary "near-Earth PS boundary (NEPS boundary)." As pointed out by recent studies, the region between the tail plasma sheet and the near-Earth plasma sheet may be a key to solving problems on dynamics of the magnetosphere [Shiokawa et al., 1998] and to studying chaotic behavior of magnetospheric particles [Zelenyi et al., 2000, 2002]. In this paper, we investigate the position of the NEPS boundary in detail and present a map showing its occurrence on the equatorial plane. We also examine characteristics of the NEPS boundary and indicate that they are very similar to characteristics of the equatorward boundary of the so-called "Wall Region" [Ashour-Abdalla et al, 1992] or "Ion Gap" [Bosqued et al, 1993; Delcourt et al., 1996], which has been observed at low altitudes. We compare the NEPS boundary with the equatorward boundary of the Wall Region (Ion Gap) identified by the low-altitude satellite Akebono. It is concluded that the boundary of the Wall Region (Ion Gap) is the field-aligned projection of the NEPS boundary detected by Geotail in the magnetosphere. This conclusion enables us to map the key region (10-15 Re) to the auroral altitudes. The result of the mapping demonstrates that the key region is projected on the latitudes of 65-70 degrees at auroral altitudes. Finally, we discuss a new method to map auroral regions to the magnetosphere without using field line models but using observed boundaries. It is

  12. Case studies of the propagation characteristics of auroral TIDS with EISCAT CP2 data using maximum entropy cross-spectral analysis

    Directory of Open Access Journals (Sweden)

    S. Y. Ma

    Full Text Available In this paper case studies of propagation characteristics of two TIDs are presented which are induced by atmospheric gravity waves in the auroral F-region on a magnetic quiet day. By means of maximum entropy cross-spectral analysis of EISCAT CP2 data, apparent full wave-number vectors of the TIDs are obtained as a function of height. The analysis results show that the two events considered can be classified as moderately large-scale TID and medium-scale TID, respectively. One exhibits a dominant period of about 72 min, a mean horizontal phase speed of about 180 m/s (corresponding to a horizontal wavelength of about 780 km directed south-eastwards and a vertical phase speed of 55 m/s for a height of about 300 km. The other example shows a dominant period of 44 min, a mean horizontal phase velocity of about 160 m/s (corresponding to a horizontal wavelength of about 420 km directed southwestwards, and a vertical phase velocity of about 50 m/s at 250 km altitude.

    Key words. Ionosphere · Auroral ionosphere · Ionosphere-atmosphere interactions · Wave propagation

  13. Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection

    Directory of Open Access Journals (Sweden)

    J. A. Davies

    Full Text Available Observations from the EISCAT VHF incoherent scatter radar system in northern Norway, during a run of the common programme CP-4, reveal a series of poleward-propagating F-region electron density enhancements in the pre-noon sector on 23 November 1999. These plasma density features, which are observed under conditions of a strongly southward interplanetary magnetic field, exhibit a recurrence rate of under 10 min and appear to emanate from the vicinity of the open/closed field-line boundary from where they travel into the polar cap; this is suggestive of their being an ionospheric response to transient reconnection at the day-side magnetopause (flux transfer events. Simultaneous with the density structures detected by the VHF radar, poleward-moving radar auroral forms (PMRAFs are observed by the Finland HF coherent scatter radar. It is thought that PM-RAFs, which are commonly observed near local noon by HF radars, are also related to flux transfer events, although the specific mechanism for the generation of the field-aligned irregularities within such features is not well understood. The HF observations suggest, that for much of their existence, the PMRAFs trace fossil signatures of transient reconnection rather than revealing the footprint of active reconnection itself; this is evidenced not least by the fact that the PMRAFs become narrower in spectral width as they evolve away from the region of more classical, broad cusp scatter in which they originate. Interpretation of the HF observations with reference to the plasma parameters diagnosed by the incoherent scatter radar suggests that as the PMRAFs migrate away from the reconnection site and across the polar cap, entrained in the ambient antisunward flow, the irregularities therein are generated by the presence of gradients in the electron density, with these gradients having been formed through structuring of the ionosphere in the cusp region in response to transient reconnection

  14. A proposal to the dissipated energy budget in the auroral ionosphere at the substorm recovery phase: Challenge from thermospheric wind variations in the pulsating aurora

    Science.gov (United States)

    Oyama, S. I.; Hosokawa, K.; Miyoshi, Y.; Shiokawa, K.; Kurihara, J.; Tsuda, T. T.; Watkins, B. J.

    2014-12-01

    Pulsating aurora is a typical phenomenon of the recovery phase of magnetic substorm and is frequently observed in the morning sector. The widely accepted generation mechanism of pulsations in precipitating electrons is related to wave-particle interactions around the equatorial plane in the magnetospheric tail. This mechanism is completely different from the discrete-arc case, which generates high-energy auroral electrons by the inverted-V type potential structure in the magnetospheric acceleration region. This potential structure induces the perpendicular electric field. The electric field is mapped down to the ionosphere, and enhances the Pedersen current as the ionospheric closure current. Since the perpendicular electric field directly relates to the Joule heating rate and the Lorentz force, thermal and kinetic energies in the thermosphere are locally increased in the vicinity of the arc rather than the inside, resulting in wind variations in the thermosphere. However, this scenario cannot be simply applied to the pulsating-auroral case because of the completely different mechanism of the auroral-electron generation, and we have believed that large energies are not dissipated in the pulsating aurora and there should be no obvious wind variations in the thermosphere. However, we found thermospheric-wind variations in the pulsating aurora during simultaneous observations with a Fabry-Perot Interferometer (557.7 nm), several cameras, and incoherent-scatter radars. This is a significantly important finding in evaluating our understanding of the energy budget in the substorm recovery phase. As mentioned above, the Joule heating process and the Lorentz force play important roles for thermospheric-wind variations. While the both cases need enhancements of the perpendicular electric field, we well know that a typical level of the convection electric field is too low to generate the wind variations in a same level as the observed in the pulsating aurora. Thus the

  15. Statistics of a parallel Poynting vector in the auroral zone as a function of altitude using Polar EFI and MFE data and Astrid-2 EMMA data

    Directory of Open Access Journals (Sweden)

    P. Janhunen

    2005-07-01

    Full Text Available We study the wave-related (AC and static (DC parallel Poynting vector (Poynting energy flux as a function of altitude in auroral field lines using Polar EFI and MFE data. The study is statistical and contains 5 years of data in the altitude range 5000–30000 km. We verify the low altitude part of the results by comparison with earlier Astrid-2 EMMA Poynting vector statistics at 1000 km altitude. The EMMA data are also used to statistically compensate the Polar results for the missing zonal electric field component. We compare the Poynting vector with previous statistical DMSP satellite data concerning the electron precipitation power. We find that the AC Poynting vector (Alfvén-wave related Poynting vector is statistically not sufficient to power auroral electron precipitation, although it may, for Kp>2, power 25–50% of it. The statistical AC Poynting vector also has a stepwise transition at R=4 RE, so that its amplitude increases with increasing altitude. We suggest that this corresponds to Alfvén waves being in Landau resonance with electrons, so that wave-induced electron acceleration takes place at this altitude range, which was earlier named the Alfvén Resonosphere (ARS. The DC Poynting vector is ~3 times larger than electron precipitation and corresponds mainly to ionospheric Joule heating. In the morning sector (02:00–06:00 MLT we find that the DC Poynting vector has a nontrivial altitude profile such that it decreases by a factor of ~2 when moving upward from 3 to 4 RE radial distance. In other nightside MLT sectors the altitude profile is more uniform. The morning sector nontrivial altitude profile may be due to divergence of the perpendicular Poynting vector field at R=3–4 RE.

    Keywords. Magnetospheric physics (Auroral phenomena; Magnetosphere-ionosphere interactions – Space plasma physics (Wave-particle interactions

  16. Auroral Data Analysis.

    Science.gov (United States)

    1978-01-04

    3.2 s required to complete NCY Mexico 87545. a Stepping sequence. “Space Environment Laboratory, National Oceanic The energy band pass of the SPS was...assumed Maxwe1~ tan p l asma . The O.N7 ±0.25 cm and a ~empe rattsre of 117 ± 24 accelerating potential is then varied , producing eV , the solid curve

  17. Comparison study between coherent echoes at VHF range and electron density estimated by Ionosphere Model for Auroral Zone

    Science.gov (United States)

    Nishiyama, Takanori; Nakamura, Takuji; Tsutsumi, Masaki; Tanaka, Yoshi; Nishimura, Koji; Sato, Kaoru; Tomikawa, Yoshihiro; Kohma, Masashi

    2016-07-01

    Polar Mesosphere Winter Echo (PMWE) is known as back scatter echo from 55 to 85 km in the mesosphere, and it has been observed by MST and IS radar in polar region during non-summer period. Since density of free electrons as scatterer is low in the dark mesosphere during winter, it is suggested that PMWE requires strong ionization of neutral atmosphere associated with Energetic Particles Precipitations (EPPs) during Solar Proton Events [Kirkwood et al., 2002] or during geomagnetically disturbed periods [Nishiyama et al., 2015]. However, studies on relationship between occurrence of PMWE and background electron density has been limited yet [Lübken et al., 2006], partly because the PMWE occurrence rate is known to be quite low (2.9%) [Zeller et al., 2006]. The PANSY (Program of the Antarctic Syowa MST/IS) radar, which is the largest MST radar in Antarctica, observed many PMWE events since it has started mesosphere observations in June 2012. We established an application method of the PANSY radar as riometer, which makes it possible to estimate Cosmic Noise Absorptions (CNA) as proxy of relative variations on background electron density. In addition, electron density profiles from 60 to 150 km altitude are calculated by Ionospheric Model for the Auroral Zone (IMAZ) [McKinnell and Friedrich, 2007] and CNA estimated by the PANSY radar. In this presentation, we would like to focus on strong PMWE during two big geomagnetic storm events, St. Patrick's Day and the Summer Solstice 2015 Event, in order to compare observed PMWE characteristics to model background electron density. On March 19 and 22, recovery phase of St. Patrick's Day Storm, sudden PMWE intensification was detected near 60 km by the PANSY radar. At the same time, strong Cosmic Noise Absorptions (CNA) of 0.8 dB and 1.0 dB were measured, respectively. However, calculated electron density profiles did not show high electron density at the altitude where the PMWE intensification were observed. On June 22, the

  18. Analytic representations of high-altitude auroral H^+ and O^+ densities, flow velocities and temperatures in terms of drivers for incorporation into global magnetospheric models

    Science.gov (United States)

    Horwitz, James; Zeng, Wen

    2008-10-01

    As new methods of describing multiple fluid species and other advances enhance the capability of global magnetospheric models to simulate the dynamics of multiple ion species, they also allow more accurate incorporation of ionospheric plasma outflows as source populations into these large scale models. Here, we shall describe the distilled results of numerous physics-based simulations of ionospheric plasma outflows influenced by auroral driving agents in terms of compact analytic expressions in terms of precipitation electron energy flux levels, characteristic energy levels of the precipitating electrons, the peak spectral wave densities for low-frequency electrostatic waves which transversely heat ionospheric ions, and solar zenith angle. The simulations are conducted with the UT Arlington Dynamic Fluid Kinetic (DyFK) ionospheric plasma transport code. We present these analytic expressions for ionospheric origin O^+ and H^+ densities, temperatures and field-aligned flow velocities at the 3 RE altitude inner boundaries of typical magnetospheric models.

  19. Observation of the June 22, 2015 G4 storm by HiT&MiS: an Echelle Spectrograph for Auroral and Airglow Studies

    Science.gov (United States)

    Aryal, S.; Hewawasam, K.; Maguire, R.; Chakrabarti, S.; Cook, T.; Martel, J.; Baumgardner, J. L.

    2015-12-01

    Observation of the June 22, 2015 G4 storm by HiT&MiS: an Echelle Spectrograph for Auroral and Airglow Studies Saurav Aryal1 , Kuravi Hewawasam1, Ryan Maguire1, Supriya Chakrabarti1, Timothy Cook1, Jason Martel1 and Jeffrey L Baumgardner2, (1) University of Massachusetts Lowell, Lowell, MA, United States, (2)Boston University, Boston, MA, United StatesA High-Throughput and Multi-slit Imaging Spectrograph (HiT&MIS) has been developed by our group. The spectrograph uses an echelle grating that operates at high dispersion orders (28-43) such that extended sources for airglow and auroral emissions can be observed at high resolution (about 0.02 nm). By using four slits (instead of the conventional one slit setup), with the appropriate foreoptics it images extended emissions along a long field of view of about 0.1° × 50°. It observes spectral regions around six prominent atmospheric emission lines (HI 656.3 nm, HI 486.1 nm, OI 557.7 nm, OI 630.0 nm, OI 777.4 nm and N+2 427.8 nm) using order sorting interference filters at the entrance slits and a filter mosaic on an image plane. We present observations from the instrument during the June 22, 2015 G4 storm. OI 557.7 nm (green line) and OI 630.0 nm (red line) showed strong brightness enhancements that lasted throughout the night from 8 P.M June 22, 2015 to 3 AM June 23,2015 when compared to the same times after the storm had passed.

  20. M-I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

    Science.gov (United States)

    Sandholt, P. E.; Farrugia, C. J.; Denig, W. F.

    2014-04-01

    We study substorms from two perspectives, i.e., magnetosphere-ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostrøm type I centered at midnight and Bostrøm type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) "snapshot" satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δ Bz/δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50-100 kV enhancements of the cross

  1. Ground-based observations of Saturn's auroral ionosphere over three days: Trends in H3+ temperature, density and emission with Saturn local time and planetary period oscillation

    Science.gov (United States)

    O'Donoghue, James; Melin, Henrik; Stallard, Tom S.; Provan, G.; Moore, Luke; Badman, Sarah V.; Cowley, Stan W. H.; Baines, Kevin H.; Miller, Steve; Blake, James S. D.

    2016-01-01

    On 19-21 April 2013, the ground-based 10-m W.M. Keck II telescope was used to simultaneously measure H3+ emissions from four regions of Saturn's auroral ionosphere: (1) the northern noon region of the main auroral oval; (2) the northern midnight main oval; (3) the northern polar cap and (4) the southern noon main oval. The H3+ emission from these regions was captured in the form of high resolution spectral images as the planet rotated. The results herein contain twenty-three H3+ temperatures, column densities and total emissions located in the aforementioned regions - ninety-two data points in total, spread over timescales of both hours and days. Thermospheric temperatures in the spring-time northern main oval are found to be cooler than their autumn-time southern counterparts by tens of K, consistent with the hypothesis that the total thermospheric heating rate is inversely proportional to magnetic field strength. The main oval H3+ density and emission is lower at northern midnight than it is at noon, in agreement with a nearby peak in the electron influx in the post-dawn sector and a minimum flux at midnight. Finally, when arranging the northern main oval H3+ parameters as a function of the oscillation period seen in Saturn's magnetic field - the planetary period oscillation (PPO) phase - we see a large peak in H3+ density and emission at ∼115° northern phase, with a full-width at half-maximum (FWHM) of ∼44°. This seems to indicate that the influx of electrons associated with the PPO phase at 90° is responsible at least in part for the behavior of all H3+ parameters. A combination of the H3+ production and loss timescales and the ±10° uncertainty in the location of a given PPO phase are likely, at least in part, to be responsible for the observed peaks in H3+ density and emission occurring at a later time than the peak precipitation expected at 90° PPO phase.

  2. M-I coupling across the auroral oval at dusk and midnight. Repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

    Energy Technology Data Exchange (ETDEWEB)

    Sandholt, P.E. [Oslo Univ. (Norway). Dept. of Physics; Farrugia, C.J. [New Hampshire Univ., Durham (United Kingdom). Space Science Center; Denig, W.F. [NOAA, Boulder, CO (United States)

    2014-07-01

    We study substorms from two perspectives, i.e., magnetosphere-ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostroem type I centered at midnight and Bostroem type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) 'snapshot' satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δB{sub z}/δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50-100 kV enhancements of the

  3. Field-aligned particle acceleration on auroral field lines by interaction with transient density cavities stimulated by kinetic Alfvén waves

    Directory of Open Access Journals (Sweden)

    P. A. Bespalov

    2006-09-01

    Full Text Available We consider the field-aligned acceleration of energetic ions and electrons which takes place on auroral field lines due to their interaction with time-varying density cavities stimulated by the strong oscillating field-aligned currents of kinetic Alfvén waves. It is shown that when the field-aligned current density of these waves increases, such that the electron drift speed exceeds the electron thermal speed, ion acoustic perturbations cease to propagate along the field lines and instead form purely-growing density perturbations. The rarefactions in these perturbations are found to grow rapidly to form density cavities, limited by the pressure of the bipolar electric fields which occur within them. The time scale for growth and decay of the cavities is much shorter than the period of the kinetic Alfvén waves. Energetic particles traversing these growing and decaying cavities will be accelerated by their time-varying field-aligned electric fields in a process that is modelled as a series of discrete random perturbations. The evolution of the particle distribution function is thus determined by the Fokker-Planck equation, with an energy diffusion coefficient that is proportional to the square of the particle charge, but is independent of the mass and energy. Steady-state solutions for the distribution functions of the accelerated particles are obtained for the case of an arbitrary energetic particle population incident on a scattering layer of finite length along the field lines, showing how the reflected and transmitted distributions depend on the typical "random walk" energy change of the particles within the layer compared to their initial energy. When this typical energy change is large compared to the initial energy, the reflected population is broadly spread in energy about a mean which is comparable with the initial energy, while the transmitted population has the form of a strongly accelerated field-aligned beam. We suggest that these

  4. An auroral westward flow channel (AWFC and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

    Directory of Open Access Journals (Sweden)

    M. L. Parkinson

    2007-02-01

    Full Text Available An auroral westward flow channel (AWFC is a latitudinally narrow channel of unstable F-region plasma with intense westward drift in the dusk-to-midnight sector ionosphere. AWFCs tend to overlap the equatorward edge of the auroral oval, and their life cycle is often synchronised to that of substorms: they commence close to substorm expansion phase onset, intensify during the expansion phase, and then decay during the recovery phase. Here we define for the first time the relationship between an AWFC, large-scale field-aligned current (FAC, the ring current, and plasmapause location. The Tasman International Geospace Environment Radar (TIGER, a Southern Hemisphere HF SuperDARN radar, observed a jet-like AWFC during ~08:35 to 13:28 UT on 7 April 2001. The initiation of the AWFC was preceded by a band of equatorward expanding ionospheric scatter (BEES which conveyed an intense poleward electric field through the inner plasma sheet. Unlike previous AWFCs, this event was not associated with a distinct substorm surge; rather it occurred during an interval of persistent, moderate magnetic activity characterised by AL~−200 nT. The four Cluster spacecraft had perigees within the dusk sector plasmasphere, and their trajectories were magnetically conjugate to the radar observations. The Waves of High frequency and Sounder for Probing Electron density by Relaxation (WHISPER instruments on board Cluster were used to identify the plasmapause location. The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE EUV experiment also provided global-scale observations of the plasmapause. The Cluster fluxgate magnetometers (FGM provided successive measurements specifying the relative location of the ring current and filamentary plasma sheet current. An analysis of Iridium spacecraft magnetometer measurements provided estimates of large-scale ionospheric FAC in relation to the AWFC evolution. Peak flows in the AWFC were located close to the peak of a Region 2

  5. Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: effect of magnetosphere-ionosphere decoupling by field-aligned auroral voltages

    Directory of Open Access Journals (Sweden)

    J. D. Nichols

    2005-03-01

    Full Text Available We consider the effect of field-aligned voltages on the magnetosphere-ionosphere coupling current system associated with the breakdown of rigid corotation of equatorial plasma in Jupiter's middle magnetosphere. Previous analyses have assumed perfect mapping of the electric field and flow along equipotential field lines between the equatorial plane and the ionosphere, whereas it has been shown that substantial field-aligned voltages must exist to drive the field-aligned currents associated with the main auroral oval. The effect of these field-aligned voltages is to decouple the flow of the equatorial and ionospheric plasma, such that their angular velocities are in general different from each other. In this paper we self-consistently include the field-aligned voltages in computing the plasma flows and currents in the system. A third order differential equation is derived for the ionospheric plasma angular velocity, and a power series solution obtained which reduces to previous solutions in the limit that the field-aligned voltage is small. Results are obtained to second order in the power series, and are compared to the original zeroth order results with no parallel voltage. We find that for system parameters appropriate to Jupiter the effect of the field-aligned voltages on the solutions is small, thus validating the results of previously-published analyses.

  6. Ion temperature anisotropy effects on threshold conditions of a shear-modified current driven electrostatic ion-acoustic instability in the topside auroral ionosphere

    Directory of Open Access Journals (Sweden)

    P. J. G. Perron

    2013-03-01

    Full Text Available Temperature anisotropies may be encountered in space plasmas when there is a preferred direction, for instance, a strong magnetic or electric field. In this paper, we study how ion temperature anisotropy can affect the threshold conditions of a shear-modified current driven electrostatic ion-acoustic (CDEIA instability. In particular, this communication focuses on instabilities in the context of topside auroral F-region situations and in the limit where finite Larmor radius corrections are small. We derived a new fluid-like expression for the critical drift which depends explicitly on ion anisotropy. More importantly, for ion to electron temperature ratios typical of F-region, solutions of the kinetic dispersion relation show that ion temperature anisotropy may significantly lower the drift threshold required for instability. In some cases, a perpendicular to parallel ion temperature ratio of 2 and may reduce the relative drift required for the onset of instability by a factor of approximately 30, assuming the ion-acoustic speed of the medium remains constant. Therefore, the ion temperature anisotropy should be considered in future studies of ion-acoustic waves and instabilities in the high-latitude ionospheric F-region.

  7. Electron-impact excitation of the singlet states of N2. I - The Birge-Hopfield system /b 1 pi u - X 1 Sigma g +/. [in auroral zones

    Science.gov (United States)

    Zipf, E. C.; Gorman, M. R.

    1980-01-01

    Results of a study of the electron-impact excitation of the b 1 pi u state of N2, one of the singlet states thought to be excited by precipitating electrons in the auroral zones, and of its predissociation and radiative relaxation through the emission of the Birge-Hopfield band system (b 1 pi u - X 1 Sigma g +) are presented. A collimated electron beam was passed through N2 gas producing a variety of atomic states through dissociative excitation, and the radiation resulting from relaxation of these states was observed by VUV and visible-IR monochromators. Absolute emission cross sections for 11 Birge-Hopfield bands are obtained for energies from threshold to 500 eV, and used to calculate the absolute transition probabilities for BH(1, v-prime) bands and the variation of the electric dipole moment with internuclear distance. With the exception of the v-prime equals 1, 5 and 6 vibrational levels, all b 1 pi u levels are found to predissociate with a specific predissociation branching ratio greater than 0.99, representing a major source of nitrogen atoms.

  8. A statistical study of the spatial distribution of Co-operative UK Twin Located Auroral Sounding System (CUTLASS) backscatter power during EISCAT heater beam-sweeping experiments

    Science.gov (United States)

    Shergill, H.; Robinson, T. R.; Dhillon, R. S.; Lester, M.; Milan, S. E.; Yeoman, T. K.

    2010-05-01

    High-power electromagnetic waves can excite a variety of plasma instabilities in Earth's ionosphere. These lead to the growth of plasma waves and plasma density irregularities within the heated volume, including patches of small-scale field-aligned electron density irregularities. This paper reports a statistical study of intensity distributions in patches of these irregularities excited by the European Incoherent Scatter (EISCAT) heater during beam-sweeping experiments. The irregularities were detected by the Co-operative UK Twin Located Auroral Sounding System (CUTLASS) coherent scatter radar located in Finland. During these experiments the heater beam direction is steadily changed from northward to southward pointing. Comparisons are made between statistical parameters of CUTLASS backscatter power distributions and modeled heater beam power distributions provided by the EZNEC version 4 software. In general, good agreement between the statistical parameters and the modeled beam is observed, clearly indicating the direct causal connection between the heater beam and the irregularities, despite the sometimes seemingly unpredictable nature of unaveraged results. The results also give compelling evidence in support of the upper hybrid theory of irregularity excitation.

  9. A fresh look at the mechanisms behind auroral E region irregularities, based on interferometry results from the March 17 storm of 2015.

    Science.gov (United States)

    St-Maurice, Jean-Pierre; Chau, Jorge

    2016-07-01

    During the strong magnetic storm of March 17, 2015, auroral echoes were detected by mid latitude radars operating at 32.5MHz and 36.2 MHz in Northern Germany. As shown in a separate presentation, thanks to several interferometry links, the retrieved spectra could be localized and superposed spectra could be separated in the presence of multiple spectral signatures from different locations with similar ranges. The radars detected four types of spectra. The first type consisted of spectra with moderate widths with a mean Doppler shift comparable to the expected ion-acoustic speed. Those are the often observed so-called Type I waves. They are Farley-Buneman waves at their peak amplitude. The second type had broad spectra with mean Doppler shifts typically less than 200 m/s. Such so-called Type II waves are routinely observed in auroral and equatorial E regions. Those waves are from Farley-Buneman waves observed from a direction perpendicular to their leading wave fronts and are therefore seen at large flow angles. The third class of echoes observed during the storm consisted of very narrow spectra with a Doppler shift that varied little from 180 m/s. These have been described as Type III waves in the literature and were never fully understood, in large part owing to a lack of localization technique. For our observations, interferometry revealed that they came from altitudes well below 100 km, with a target motion of 800 m/s or more in spite of the small Doppler shift. This contrasted with the fourth type, which came from the upper part of the unstable E region and was made once again of very narrow spectra moving at close to the line-of-sight velocity (as found through target motion) when the plasma drift was particularly large, of the order of 1400 m/s. This presentation will show that the Type III waves were in great agreement with the notion of maximum amplitude unstable Farley-Buneman waves excited by very large electric fields in a region strongly affected by non

  10. Overview of the Equatorial Electrojet and Related Ionospheric Current Systems

    Science.gov (United States)

    2007-11-02

    movement of the EEJ. 39 100 ABz 1000 0 1000 26000 DIP DISTANCE (kin) Figure 3-11. Latitudinal Profiles of the Daily Ranges of Northward Magnetic Field ABx...times larger than that of the EEJ. ISO -INTENSITY CONTOURS OF HORIZONTAL CURRENT DENSITY C.. , I, . I -" -- UNIT: KTFA/m= 180- 70- (j V vI 160 i (. % Eý

  11. French participation in the International Equatorial Electrojet Year

    Directory of Open Access Journals (Sweden)

    Y. Cohen

    Full Text Available Without abstract

    Acknowledgements. The IEEY studies in the African sector were made possible by the participation of a large number of institutes. Funding was provided by the Ministère Français de la Coopération (Département de la Recherche et des Formations, and Département Télécommunications; ORSTOM (Département Terre Océan Atmosphère; CNET (France-Telecom Centre Lannion; the Ministère Français de la Recherche et de la Technologie; Centre National de la Recherche Scientifique (Département Sciences de l'Univers; the Centre à l'Energie Atomique; the Université Paris-Sud; Abidjan University, Ivory Coast; Dakar University, Senegal. We would like to express our deep gratitude to the many colleagues who have participated in the success of this experiment through their enormous personal commitment, to the Editorial Board of Annales Geophysicae and particularly to Sylviane Perret for producing this special issue.

  12. Observations of ULF wave related equatorial electrojet and density fluctuations

    Science.gov (United States)

    Yizengaw, E.; Zesta, E.; Biouele, C. M.; Moldwin, M. B.; Boudouridis, A.; Damtie, B.; Mebrahtu, A.; Anad, F.; Pfaff, R. F.; Hartinger, M.

    2013-10-01

    We report on Pc5 wave related electric field and vertical drift velocity oscillations at the equator as observed by ground magnetometers for an extended period on 9 August 2008. We show that the magnetometer-estimated equatorial E×B drift oscillates with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. We also show ionospheric density fluctuations during the period when we observed ULF wave activity. At the same time, we detect the ULF activity on the ground using ground-based magnetometer data from the African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Upstream solar wind conditions are provided by the ACE spacecraft. We find that the wave power observed on the ground also occurs in the upstream solar wind and in the magnetosphere. All these observations demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. While no direct drift measurements from equatorial radars exist for the 9 August 2008 event, we used JULIA 150 km radar drift velocities observed on 2 May 2010 and found similar fluctuations with the period of 5-8 min, as a means of an independent confirmation of our magnetometer derived drift dynamics.

  13. Dependence of the open-closed field line boundary in Saturn's ionosphere on both the IMF and solar wind dynamic pressure: comparison with the UV auroral oval observed by the HST

    Directory of Open Access Journals (Sweden)

    E. S. Belenkaya

    2008-02-01

    Full Text Available We model the open magnetic field region in Saturn's southern polar ionosphere during two compression regions observed by the Cassini spacecraft upstream of Saturn in January 2004, and compare these with the auroral ovals observed simultaneously in ultraviolet images obtained by the Hubble Space Telescope. The modelling employs the paraboloid model of Saturn's magnetospheric magnetic field, whose parameters are varied according to the observed values of both the solar wind dynamic pressure and the interplanetary magnetic field (IMF vector. It is shown that the open field area responds strongly to the IMF vector for both expanded and compressed magnetic models, corresponding to low and high dynamic pressure, respectively. It is also shown that the computed open field region agrees with the poleward boundary of the auroras as well as or better than those derived previously from a model in which only the variation of the IMF vector was taken into account. The results again support the hypothesis that the auroral oval at Saturn is associated with the open-closed field line boundary and hence with the solar wind interaction.

  14. IMF dependence of the open-closed field line boundary in Saturn's ionosphere, and its relation to the UV auroral oval observed by the Hubble Space Telescope

    Directory of Open Access Journals (Sweden)

    E. S. Belenkaya

    2007-06-01

    Full Text Available We study the dependence of Saturn's magnetospheric magnetic field structure on the interplanetary magnetic field (IMF, together with the corresponding variations of the open-closed field line boundary in the ionosphere. Specifically we investigate the interval from 8 to 30 January 2004, when UV images of Saturn's southern aurora were obtained by the Hubble Space Telescope (HST, and simultaneous interplanetary measurements were provided by the Cassini spacecraft located near the ecliptic ~0.2 AU upstream of Saturn and ~0.5 AU off the planet-Sun line towards dawn. Using the paraboloid model of Saturn's magnetosphere, we calculate the magnetospheric magnetic field structure for several values of the IMF vector representative of interplanetary compression regions. Variations in the magnetic structure lead to different shapes and areas of the open field line region in the ionosphere. Comparison with the HST auroral images shows that the area of the computed open flux region is generally comparable to that enclosed by the auroral oval, and sometimes agrees in detail with its poleward boundary, though more typically being displaced by a few degrees in the tailward direction.

  15. Polyarnye siyaniya sistemy avroral'nogo ovala kak kosmoloficheskij obraz drevnej mifologii %t The northern light of the auroral oval system as a cosmological concept of the archaic mythology

    Science.gov (United States)

    Alekseeva, L. M.

    Since archaic epochs people attentively observe the sky. They used to associate the sky phenomena with gods, heroes, spirits, etc. People interpreted the regularities in the motion of celestial objects in terms of their mythological model of the Universe. These observations and interpretations were first steps of the archaeoastronomy. Many remarkable features are inherent in the patterns of northern lights of the auroral oval system. Their manifestations are fairly regular. Did the ancients observe and some how classify these northern light phenomena? If yes, with which mythological personages were they associated? When were studies of the polar lights initiated? The present work is an attempt to answer these questions. We shall see that the ancient people assumed the spirit-world to be situated on the North. If so, it should manifest itself in spectacular polar aurorae. The specifically northern mythic cosmology formed the basis for Slavic fairy tales (theme of the Serpent and Serpent Fighter) and folk-beliefs. Other inhabitants of snowy latitudes should also manifest similar views. Studying the mythological reflections of typical auroral phenomena, it is possible to trace up long-standing ideological trends from the late glaciation epoch to the present time. Our results can help geophysicists in studying paleoauroral phenomena.

  16. Ionospheric Response to Solar Wind Pressure Pulses Under Northward IMF Conditions

    Directory of Open Access Journals (Sweden)

    Kan Liou

    2013-01-01

    Full Text Available Enhancements of aurora and auroral electrojets in response to sudden compression of the magnetosphere by shocks/pressure pulses are well known and have been attributed by some to compression-enhanced magnetic field reconnection. To examine such a view, we analyze a fortuitous event that is comprised of a series of pressure pulses (< 20 min on November 8, 2000. These pressure pulses were preceded by a large, northward interplanetary magnetic field (IMF that lasted more than 15 hours such that effects from reconnection can be minimized. Auroral images acquired by ultraviolet imager on board the Polar satellite clearly show intensifications of the aurora that occurred first near local noon and progressively extended from dayside to nightside. The area-integrated global auroral power reached ~30 gigawatts (GW. It is also found that the global auroral power is well correlated with the solar wind dynamic pressure (correlation coefficient r ~0.90, rather than the change in the solar wind dynamic pressure. In-situ measurements of particle data from the Defense Meteorological Satellite Program satellite indicate that the magnetospheric source for the pressure-enhanced auroras is most likely the central plasma sheet. Other ionospheric parameters such as the auroral electrojet (AE index, magnetic storm index (Sym-H, and the cross polarcap potential drop also show a one-to-one correspondence to the pressure pulses. In one instance the auroral electrojets AE index reached more than 200 nT, the cross polar-cap potential drop (ÎŚpc inferred from the SuperDARN radar network ionospheric plasma convection increased to ~60 kV. The observed increases in the auroral emissions, AE, and polar cap potential were not associated with substorms. Our result strongly suggests that solar wind pressure pulses are an important source of geomagnetic activity during northward IMF periods.

  17. Anne-Aurore Inquimbert, Un officier français dans la guerre d’Espagne. Carrière et écrits d’Henri Morel (1919-1944

    Directory of Open Access Journals (Sweden)

    Antoine Fraile

    2010-07-01

    Full Text Available L’ouvrage d’Anne-Aurore Inquimbert est une biographie de la carrière militaire d’Henri Morel depuis la fin de la Première Guerre Mondiale jusqu’à sa mort en déportation en 1944. Il retrace la trajectoire d’un militaire atypique que l’auteur définit commereprésentatif d’une certaine élite française, romantique, érudite et bourgeoise pour laquelle la liberté intellectuelle est partie intégrante d’un système de valeurs. En optant pour une carrière militaire, Henri Morel s’est volontairement excl...

  18. A parameter model of auroral emissions and particle precipitation near magnetic noon%磁正午附近极光强度与沉降粒子能量关系的参数模型

    Institute of Scientific and Technical Information of China (English)

    邢赞扬; 杨惠根; 吴振森; 胡泽骏; 刘俊明; 张清和; 胡红桥

    2013-01-01

    极光是日地能量耦合过程中粒子沉降到极区电离层的最直观表现,对于理解地球空间环境及预测空间天气具有重要作用.本文利用2003-2009年的北极黄河站的多波段地面极光观测,结合DMSP卫星粒子沉降探测,对磁正午附近的极光强度与沉降粒子沉降能量之间的关系进行了定量研究.统计结果表明,在10-13磁地方时(MLT)630.0 nm的极光发光占主导,以低能粒子沉降为主;而在13-14MLT,630.0 nm/427.8 nm极光强度比值降低,沉降粒子能量较高.另外,利用极光强度与沉降电子的能通量以及极光强度比值与平均能量之间的函数关系,初步建立了北极黄河站磁正午附近极光强度与沉降粒子能量关系的反演参数模型,为将来空间天气的监测服务.%The aurora is one of the most significant visible manifestations of the dynamic processes associated with the precipitation of particles into the polar ionosphere generated by the solar-terrestrial interactions,which has played an important role in understanding our Earth's environment and predicting the space weather.Using high temporal resolution optical data obtained from the three-wavelength all-sky imagers at Yellow River Station (YRS) in the Arctic,together with the particle precipitation data measured by the DMSP satellites,we investigated the quantitative relationship between the auroral intensities and the energy features of the precipitated particles near magnetic noon.The statistical results indicated that the soft auroral electron precipitation was dominated near magnetic noon during 10-13MLT with 630.0 nm auroral emissions.The I(630.0 nm)/I(427.8 nm) ratio decreased as the intensity of 427.8 nm increasedin the 13-14MLT sector,suggesting the energy of the precipitated particles was getting higher.In addition,the intensity of 427.8 nm was dependent on the total energy flux of the precipitating electrons and the I(630.0 nm)/I(427.8 nm) ratio was related to the

  19. Magnetic local time dependence of geomagnetic disturbances contributing to the AU and AL indices

    DEFF Research Database (Denmark)

    Tomita, S; Nose´, M; Iyemori, T;

    2010-01-01

    The Auroral Electrojet (AE) indices, which are composed of four indices (AU, AL, AE, and AO), are calculated from the geomagnetic field data obtained at 12 geomagnetic observatories that are located in geomagnetic latitude (GMLAT) of 61.7°-70°. The indices have been widely used to study magnetic...... activity in the auroral zone. In the present study, we examine magnetic local time (MLT) dependence of geomagnetic field variations contributing to the AU and AL indices. We use 1-min geomagnetic field data obtained in 2003. It is found that both AU and AL indices have two ranges of MLT (AU: 15:00-22:00MLT...

  20. Dayside and nightside contributions to cross-polar cap potential variations: the 20 March 2001 ICME case

    Directory of Open Access Journals (Sweden)

    Y. L. Andalsvik

    2011-11-01

    Full Text Available We investigate the association between temporal-spatial structure of polar cap convection and auroral electrojet intensifications during a 5-h-long interval of strong forcing of the magnetosphere by an ICME/Magnetic cloud on 20 March 2001. We use data from coordinated ground-satellite observations in the 15:00–20:00 MLT sector. We take advantage of the good latitudinal coverage in the polar cap and in the auroral zone of the IMAGE chain of ground magnetometers in Svalbard – Scandinavia – Russia and the stable magnetic field conditions in ICMEs. The electrojet events are characterized by a sequence of 10 min-long AL excursions to −1000/−1500 nT followed by poleward expansions and auroral streamers. These events are superimposed on a high disturbance level when the AL index remains around −500 nT for several hours. These signatures are different from those appearing in classical substorms, most notably the absence of a complete recovery phase when AL usually reaches above −100 nT. We concentrate on polar cap convection in both hemispheres (DMSP F13 data in relation to the ICME By conditions, electrojet intensifications, and the global UV auroral configuration obtained from the IMAGE spacecraft. The temporal evolution of convection properties such as the cross-polar cap potential (CPCP drop and flow channels at the dawn/dusk polar cap (PC boundaries around the time of the electrojet events are investigated. This approach allows us to distinguish between dayside (magnetopause reconnection and nightside (magnetotail reconnection sources of the PC convection events within the context of the expanding-contracting model of high-latitude convection in the Dungey cycle. Inter-hemispheric symmetries/asymmetries in the presence of newly-discovered convection channels at the dawn or dusk side PC boundaries are determined.

  1. Magnetosheath control of solar wind-magnetosphere coupling efficiency

    Science.gov (United States)

    Pulkkinen, T. I.; Dimmock, A. P.; Lakka, A.; Osmane, A.; Kilpua, E.; Myllys, M.; Tanskanen, E. I.; Viljanen, A.

    2016-09-01

    We examine the role of the magnetosheath in solar wind-magnetosphere-ionosphere coupling using the Time History of Events and Macroscale Interactions during Substorms plasma and magnetic field observations in the magnetosheath together with OMNI solar wind data and auroral electrojet recordings from the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer chain. We demonstrate that the electric field and Poynting flux reaching the magnetopause are not linear functions of the electric field and Poynting flux observed in the solar wind: the electric field and Poynting flux at the magnetopause during higher driving conditions are lower than those predicted from a linear function. We also show that the Poynting flux normal to the magnetopause is linearly correlated with the directly driven part of the auroral electrojets in the ionosphere. This indicates that the energy entering the magnetosphere in the form of the Poynting flux is directly responsible for driving the electrojets. Furthermore, we argue that the polar cap potential saturation discussed in the literature is associated with the way solar wind plasma gets processed during the bow shock crossing and motion within the magnetosheath.

  2. M-I coupling across the Harang reversal during storm--substorm activity driven by an interplanetry ICMEs

    Science.gov (United States)

    Farrugia, C. J.; Sandholt, P. E.; Denig, W. F.

    2013-12-01

    By ground - satellite conjunctions across the auroral oval at dusk we study events of dynamical magnetosphere--ionosphere (M-I) coupling from the plasma sheet - ring current system via R1 and R2 field-aligned currents (FACs) during auroral electrojet activations appearing on the poleward and equatorward sides of the Harang reversal (HR), respectively. The interval of ICME passage at Earth we study is characterized by repetitive substorm activity appearing as a series of westward expansions--eastward retreats of the westward electrojet (WEJ) across the 1800 MLT meridian. Harang region-north (HR-N) is characterized by R1 FAC closure, WEJ activity, poleward boundary intensifications (PBIs) - equatorward - moving auroral streamers (inverted V - arcs), and (at different times) poleward auroral expansions. Harang region-south (HR-S) is characterized by R2 FAC closure leading to eastward electrojet (EEJ) activity and precipitation in the southern auroral branch. Using this approach we documented the detailed temporal evolution of polar cap convection, as derived from the PCN index, in relation to direct observations of the dynamical behaviour of the two basic branches of the substorm current system, i. e. the R2 FAC coupling from the partial ring current (PRC) and the R1 FAC coupling from the plasma sheet. We distinguish between two activity levels: (i) major AL-excursions beyond -1000 nT (accompanied by large-scale field dipolarizations in the inner magnetotail), followed by SYM-H dips (plasma injections enhancing the PRC) and R2 FAC - EEJ enhancements, and (ii) partial AL - recovery (AL within -300 to -600 nT) characterized by a series of M - I coupling events with manifestations on both sides of the HR, including streamer events in HR-N, leading to equatorward/poleward motions of the HR boundary.

  3. Intermittency of the turbulent processes in the Earth's magnetosphere detected from the ground-based measurements

    Science.gov (United States)

    Stepanova, Marina; Foppiano, Alberto; Ovalle, Elias; Antonova, Elizavieta; Troshichev, Oleg

    2008-11-01

    Turbulent processes in the Earth's magnetosphere are reflected in the dynamical behavior of the geomagnetic indices and other parameters determined from ground based observations. Intermittent properties of one minute Polar Cap (PC) index and auroral radio wave absorption are studied using 1995-2000 data sets. It was found that the probability distribution functions (PDFs) of both PC-index and absorption fluctuations display a strong non-Gaussian shape. This indicates that they are not characterized by a global time self-similarity but rather exhibit intermittency, as previously reported for solar wind velocity and auroral electrojet index values. In the case of the auroral absorption it was also found that intermittency strongly depends on the magnetic local time, being largest in the nighttime sector. This shows that the acceleration of precipitating particles is intermittent, especially near the substorm eye, where the level of turbulence increases. Application of the Local Intermittency Measure (LIM) technique confirms the aforementioned results to a better precision.

  4. What is the appropriate coordinate system for magnetometer data when analyzing ionospheric currents?

    CERN Document Server

    Laundal, K M

    2016-01-01

    In this paper we investigate which coordinate representation is most appropriate when analyzing ground magnetometer data in terms of ionospheric currents, in particular the westward electrojet. The $\\textit{AL}$ and the recently introduced $\\textit{SML}$ index are frequently used as monitors of the westward electrojet. Both indices are based on ground magnetometers at auroral latitudes. From these magnetometers, the largest perturbation in the southward direction is selected as the $\\textit{ AL/SML }$ index at 1 min cadence. The southward component is defined as antiparallel to the orientation of the horizontal part of the Earths' main field, $\\textbf{B}_{0, \\textit{H}}$. The implicit assumption when using these indices as a monitor of the westward electrojet is that the electrojet flows perpendicular to $\\textbf{B}_{0, \\textit{H}}$. However, $\\textbf{B}_{0, \\textit{H}}$ is, in general, not perpendicular to the westward direction in coordinate systems that take nondipole terms of the Earth's magnetic field in...

  5. Westward moving dynamic substorm features observed with the IMAGE magnetometer network and other ground-based instruments

    Directory of Open Access Journals (Sweden)

    H. Lühr

    Full Text Available We present the ground signatures of dynamic substorm features with particular emphasis on the event interpretation capabilities provided by the IMAGE magnetometer network. This array covers the high latitudes from the sub-auroral to the cusp/cleft region. An isolated substorm on 11 Oct. 1993 during the late evening hours exhibited many of well-known features such as the Harang discontinuity, westward travelling surge and poleward leap, but also discrete auroral forms, known as auroral streamers, appeared propagating westward along the centre of the electrojet. Besides the magnetic field measurements, there were auroral observations and plasma flow and conductivity measurements obtained by EISCAT. The data of all three sets of instruments are consistent with the notion of upward field-aligned currents associated with the moving auroral patches. A detailed analysis of the electrodynamic parameters in the ionosphere, however, reveals that they do not agree with the expectations resulting from commonly used simplifying approximations. For example, the westward moving auroral streamers which are associated with field-aligned current filaments, are not collocated with the centres of equivalent current vortices. Furthermore, there is a clear discrepancy between the measured plasma flow direction and the obtained equivalent current direction. All this suggests that steep conductivity gradients are associated with the transient auroral forms. Also self-induction effects in the ionosphere may play a role for the orientation of the plasma flows. This study stresses the importance of multi-instrument observation for a reliable interpretation of dynamic auroral processes.

    Keywords. Ionosphere (Auroral ionosphere; Electric fields and currents; Ionosphere-magnetosphere interactions.

  6. Electric currents of a substorm current wedge on 24 February 2010

    Science.gov (United States)

    Connors, Martin; McPherron, Robert L.; Anderson, Brian J.; Korth, Haje; Russell, Christopher T.; Chu, Xiangning

    2014-07-01

    The three-dimensional "substorm current wedge" (SCW) was postulated by McPherron et al. (1973) to explain substorm magnetic perturbations. The origin and coherence as a physical system of this important paradigm of modern space physics remained unclear, however, with progress hindered by gross undersampling, and uniqueness problems in data inversion. Complementing AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment) space-derived radial electric currents with ground magnetic data allowing us to determine currents from the ionosphere up, we overcome problems of uniqueness identified by Fukushima (1969, 1994). For a substorm on 24 February 2010, we quantify SCW development consistently from ground and space data. Its westward electrojet carries 0.5 MA in the more poleward part of the auroral oval, in Region 1 (R1) sense spanning midnight. The evening sector electrojet also feeds into its upward current. We thus validate the SCW concept and obtain parameters needed for quantitative study of substorms.

  7. Artificial periodic irregularities in the auroral ionosphere

    Directory of Open Access Journals (Sweden)

    M.T. Rietveld

    Full Text Available Artificial periodic irregularities (API are produced in the ionospheric plasma by a powerful standing electromagnetic wave reflected off the F region. The resulting electron-density irregularities can scatter other high-frequency waves if the Bragg scattering condition is met. Such measurements have been performed at mid-latitudes for two decades and have been developed into a useful ionospheric diagnostic technique. We report here the first measurements from a high-latitude station, using the EISCAT heating facility near Tromsø, Norway. Both F-region and lower-altitude ionospheric echoes have been obtained, but the bulk of the data has been in the E and D regions with echoes extending down to 52-km altitude. Examples of API are shown, mainly from the D region, together with simultaneous VHF incoherent-scatter-radar (ISR data. Vertical velocities derived from the rate of phase change during the irregularity decay are shown and compared with velocities derived from the ISR. Some of the API-derived velocities in the 75–115-km height range appear consistent with vertical neutral winds as shown by their magnitudes and by evidence of gravity waves, while other data in the 50–70-km range show an unrealistically large bias. For a comparison with ISR data it has proved difficult to get good quality data sets overlapping in height and time. The initial comparisons show some agreement, but discrepancies of several metres per second do not yet allow us to conclude that the two techniques are measuring the same quantity. The irregularity decay time-constants between about 53 and 70 km are compared with the results of an advanced ion-chemistry model, and height profiles of recorded signal power are compared with model estimates in the same altitude range. The calculated amplitude shows good agreement with the data in that the maximum occurs at about the same height as that of the measured amplitude. The calculated time-constant agrees very well with the data below 60 km but is larger above 60 km by a factor of up to 2 at 64 km. The comparisons with the model are considered to be a good basis for more refined comparisons.

  8. Variation of surface electric field during geomagnetic disturbed period at Maitri, Antarctica

    Indian Academy of Sciences (India)

    N Jeni Victor; C Panneerselvam; C P Anil Kumar

    2015-12-01

    The paper discusses on the variations of the atmospheric vertical electric field measured at sub-auroral station Maitri (70°75′S, 11°75′E), and polar station Vostok (78.5°S, 107°E) during the geomagnetic disturbances on 25–26 January 2006. Diurnal variation of surface electric field measured at Maitri shows a similar variation with worldwide thunderstorm activity, whereas the departure of the field is observed during disturbed periods. This part of the field corresponds to the magnetospheric/ionospheric (an additional generator in the polar regions) voltage generators. Solar wind parameters and planetary indices represent the temporal variation of the disturbances, and digital fluxgate magnetometer variation continuously monitored to trace the auroral movement at Maitri. We have observed that the electrojet movement leaves its signature on vertical and horizontal components of the DFM in addition; the study infers the position of auroral current wedge with respect to Maitri. To exhibit the auroral oval, OVATION model is obtained with the aid of DMSP satellite and UV measurements. It is noted that the Maitri is almost within the auroral oval during the periods of disturbances. To examine the simultaneous changes in the vertical electric field associated with this magnetic disturbance, the dawn–dusk potential is studied for every UT hours; the potential was obtained from Weimer model and SuperDARN radar. The comparison reveals the plausible situation for the superposition of dawn–dusk potential on surface electric field over Maitri. This observation also shows that the superposition may not be consistent with the phase of the electrojet. Comparison of surface electric field at Maitri and Vostok shows that the parallel variation exhibits with each other, but during the period of geomagnetic disturbances, the influence is not much discerned at Vostok.

  9. Observation and theory of the radar aurora

    Energy Technology Data Exchange (ETDEWEB)

    Sahr, J.D.

    1990-01-01

    Plasma density irregularities occurring near the Aurora Borealis cause scattering of HF, VHF, and UHF radio waves. Analysis of the resulting radar signal provides great detail about the spatial and temporal characteristics of these auroral E region irregularities. Observations are presented of the radar aurora from recent campaigns in northern Sweden. After reviewing the basic theory and observations of auroral electrojet irregularities, a simple nonlinear fluid theory of electrojet ion-acoustic waves is introduced, and reduced to a form of the three-wave interaction equations. This theory provides a simple mechanism for excitation of linearly stable waves at large aspect and flow angles, as well as a prediction of the power spectra that a coherent scatter radar should observe. In addition, this theory may be able to account for type 3 waves without resorting to ion gyro modes, such as the electrostatic ion-cyclotron wave. During the course of the research a simple new radar transmitting mode and signal processing algorithm was generated which very simply solves a frequency aliasing problem that often occurs in CUPRI auroral radar studies. Several new radar data analysis routines were developed, including the principally cross-beam image and scatter plots of the second versus first moments of the power spectrum of the irregularities. Analysis of vertical interferometer data shows that type 3 waves originate at ordinary electrojet altitudes, not in the upper E region, from which it is concluded that the electrostatic ion-cyclotron mode does not generate type 3 waves. The measured height of type 3 waves and other spectral analyses provide support for the pure ion-acoustic theory of type 3 waves. Suggestions are offered for hardware improvements to the CUPRI radar, new experiments to test new and existing theories.

  10. Simulations of Wind Field Effect on Two-Stream Waves in the Equatorial Electrojet

    Directory of Open Access Journals (Sweden)

    Chi-Lon Fern

    2009-01-01

    Full Text Available The wind field effect on the phase veloc i ties of 3- to 10-me ter Farley-Buneman two-stream waves in the equato rial E region ion o sphere at al titudes in the range of 95 - 110 km is stud ied by nu mer i cal simu la tion. The behav ior of this two-stream wave in the uni form wind field Un in a plane per pen dic u lar to the Earth’s mag netic field is simu lated with a two-di men sional two-fluid code in which elec tron in er tia is ne glected while ion in er tia is re tained. It is con firmed that, the thresh old con di tion for the ap pear ance of two-stream waves is VD C U th » + s + n (1 / cos Y0 q ; and the phase ve loc ity of the two-stream wave at the thresh old con di tion is Vp » Cs + Un cos q, where q is the ele va tion an gle of the wave prop a ga tion in a limited range and Y0 = ninnen / WiWe. The first formula in di cates that the wind field paral lel (anti-par al lel to the elec tron drift ve loc ity will raise (lower the thresh old drift ve loc ity by the amount of the wind speed. This means that par al lel wind is a sta ble fac tor, while anti-paral lel wind is an un sta ble fac tor of two-stream waves. This may ex plain why high speed (larger than acous tic speed two-stream waves were rarely ob served, since larger thresh old drift veloc ity de mands larger po larization elec tric field. The result of the simu la tions at the sat u ra tion stage show that when VD was only slightly larger than VD th , the hor i zon tal phase ve loc ity of the two-stream wave would grad u ally down-shift to the thresh old phase ve loc ity Cs + Un. The physical implications of which are discussed

  11. Unified theory of type I and type II irregularities in the equatorial electrojet

    Science.gov (United States)

    Sudan, R. N.

    1983-01-01

    A nonlinear unified theory of type I and II irregularities is presented that explains their principal observed characteristics. The power spectrum is predicted by using Kolmogoroff-type conservation law for the power flow in cascading eddies.

  12. Magnetotelluric investigation in West Greenland - considering the polar electrojet, ocean and fjords

    DEFF Research Database (Denmark)

    Lauritsen, Nynne Louise Berthou

    A magnetotelluric survey has been conducted in North West Greenland, with the purpose of investigating the subsurface. The results of two processing techniques are presented, a single station robust processing and a multiple station processing. The multiple station processing tries to eliminate...... data originating from other sources than the plane wave by removing incoherent noise between stations and selecting time periods from an eigenvalue criteria. It is successful for periods below 55 s, but has to undergo further investigation at longer periods. The two processing techniques show similar...... results, however the multiple station technique improves the data quality around 1 s compared to the single station technique. Different challenges are connected with the survey location, where ocean and fjord systems have a large impact on the transferfunctions. A 3D model study of the impact of fjords...

  13. Comparison between SuperDARN flow vectors and equivalent ionospheric currents from ground magnetometer arrays

    DEFF Research Database (Denmark)

    Weygand, J. M.; Amm, O.; Angelopoulos, V.;

    2012-01-01

    Equivalent ionospheric currents obtained with the spherical elementary current systems (SECS) method and derived from nearly 100 ground magnetometers spread over North America and Greenland are compared with ionospheric flow vectors measured by the SuperDARN radars during both the summer and winter...... seasons. This comparison is done over a range of spatial separations, magnetic latitudes, magnetic local times, and auroral electrojet activity to investigate under what conditions the vectors are anti-parallel to one another. Our results show that in general the equivalent ionospheric currents are anti...

  14. Analysis of Sqp current systems by using corrected geomagneticcoordinates

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The Spq equivalent current system of the quiet day geomagnetic variation in the polar region is very complicated. It is composed of several currents, such as the ionospheric dynamo current and the auroral electrojet caused by the field-aligned current. Spq is unsymmetrical in both polar regions. In this paper, the Spq current systems are analyzed in the corrected geomagnetic coordinates (CGM) instead of the conventional geomagnetic coordinates (GM), and the symmetries of the Spq current indifferent systems are compared. Then the causes of Spq asymmetry in the GM coordinates are discussed; the effects of each component in Spq are determined.

  15. Relations of PC indices to further geophysical activity parameters.

    Science.gov (United States)

    Stauning, P.

    2012-04-01

    The Polar Cap (PC) indices, PCN for the index values derived from Thule magnetic data and PCS derived from Vostok data, relate to the polar cap ionospheric plasma convection driven mainly by the interaction of the solar wind with the magnetosphere. Thus, the PC indices serve to monitor the input power from the solar wind which drives a range of geophysical disturbances such as magnetic storms and substorms, energization of the plasma trapped in the Earth's near space, auroral activity, and heating of the upper atmosphere. The presentation will demonstrate the relations between the PC indices and further parameters and indices used to describe geophysical activity such as polar cap potentials, auroral electrojet activity, Joule and particle heating of the upper atmosphere, mid-latitude magnetic variations, and ring current indices Dst, SYM-H and ASY-H.

  16. Application of Polar Cap (PC) indices in analyses and forecasts of geophysical conditions

    Science.gov (United States)

    Stauning, Peter

    2016-07-01

    The Polar Cap (PC) indices could be considered to represent the input of power from the solar wind to the Earth's magnetosphere. The indices have been used to analyse interplanetary electric fields, effects of solar wind pressure pulses, cross polar cap voltages and polar cap diameter, ionospheric Joule heating, and other issues of polar cap dynamics. The PC indices have also been used to predict auroral electrojet intensities and global auroral power as well as ring current intensities. For specific space weather purposes the PC indices could be used to forecast substorm development and predict associated power line disturbances in the subauroral regions. The presentation shall outline the general background for applying the PC indices in analyses or forecasts of solar wind-magnetosphere-ionosphere interactions and provide illustrative examples of the use of the Polar Cap indices in specific cases

  17. Diagnosis of Auroral Dynamics Using Global Auroral Imaging with Emphasis on Large-Scale Evolutions

    Science.gov (United States)

    1989-09-01

    Figures 1 and 2. These false-colar images of the aurora borealis (Figure 1) and the aurora australis (Figure 2), with overlays of the coastlines, show...1985]. A coastline map is superposed on this false-color image of the aurora borealis at ultraviolet wavelengths 123-155 nm (filter 2). Principal...polar regions: The aurora borealis at northern latitudes and aurora australis at southern latitudes. Earth’s limb and coastal outlines are overlaid on

  18. Calculation of Classical Polar-Activity Indices Using Their Modern Variants

    Science.gov (United States)

    Barkhatov, N. A.; Korolev, A. V.; Levitin, A. E.; Sakharov, S. Yu.

    2004-03-01

    At present, the auroral-electrojet AE, AU, and AL indices are calculated using a smaller number of stations than earlier. This influences the accuracy of estimates of the magnetospheric activity components, which are performed using the relationships with modern indices AE8 (obtained from the data of 8 stations) substituted instead of the classical indices AE12 (obtained from the data of 12 stations). In this paper, we develop an artificial neural-network (ANN) algoritm for recalculating the classical polar-activity indices from modern ones. It is demonstrated that the developed ANN is capable of retrieving the AE12-index from data of 8 stations (AE8) with efficiency reaching 90% in some cases. The results obtained allow one to estimate the error in the representation of the auroral-electrojet activity by modern AE8 indices as compared with the ones introduced into geophysical research by their creators. We also develop a retrieval technique for polar indices, which employs data on solar-wind parameters.

  19. On induction effects of geomagnetic daily variations from equatorial electrojet and solar quiet sources at low and middle latitudes

    DEFF Research Database (Denmark)

    Kuvshinov, A.; Manoj, C; Olsen, Nils;

    2007-01-01

    by the comprehensive model of Sabaka et al.(2004). The three-dimensional (3-D) conductivity model of the Earth includes oceans of laterally variable conductance and a spherical conductor (1-D) underneath. Our model studies demonstrate that induction effects in Z due to the EEJ are negligible everywhere inland for all...... local times. At CHAMP altitude (400 km) the magnetic signal induced by EEJ above the oceans does not exceed 2–5% of the external field during local noon. This, in particular, means that considering the induction effects is not necessary when modeling the EEJ current strength from inland surface magnetic...... measurements and/or satellite data. As expected, induction in the oceans strongly affects the Sq field. The model studies show that the anomalous induction effect (defined as the difference between results obtained with 1-D and 3-D conductivity models) of Sq is substantial at CHAMP altitude,comprising 50...

  20. Reconnection electric field estimates and dynamics of high-latitude boundaries during a substorm

    Directory of Open Access Journals (Sweden)

    T. Pitkänen

    2009-05-01

    Full Text Available The dynamics of the polar cap and the auroral oval are examined in the evening sector during a substorm period on 25 November 2000 by using measurements of the EISCAT incoherent scatter radars, the north-south chain of the MIRACLE magnetometer network, and the Polar UV Imager.

    The location of the polar cap boundary (PCB is estimated from electron temperature measurements by the mainland low-elevation EISCAT VHF radar and the 42 m antenna of the EISCAT Svalbard radar. A comparison to the poleward auroral emission (PAE boundary by the Polar UV Imager shows that in this event the PAE boundary is typically located 0.7° of magnetic latitude poleward of the PCB by EISCAT. The convection reversal boundary (CRB is determined from the 2-D plasma drift velocity extracted from the dual-beam VHF data. The CRB is located 0.5–1° equatorward of the PCB indicating the existence of viscous-driven antisunward convection on closed field lines.

    East-west equivalent electrojets are calculated from the MIRACLE magnetometer data by the 1-D upward continuation method. In the substorm growth phase, electrojets together with the polar cap boundary move gradually equatorwards. During the substorm expansion phase, the Harang discontinuity (HD region expands to the MLT sector of EISCAT. In the recovery phase the PCB follows the poleward edge of the westward electrojet.

    The local ionospheric reconnection electric field is calculated by using the measured plasma velocities in the vicinity of the polar cap boundary. During the substorm growth phase, values between 0 and 10 mV/m are found. During the late expansion and recovery phase, the reconnection electric field has temporal variations with periods of 7–27 min and values from 0 to 40 mV/m. It is shown quantitatively, for the first time to our knowledge, that intensifications in the local reconnection electric field correlate with appearance of auroral poleward boundary intensifications (PBIs

  1. Intermittency of the turbulent processes in the Earth's magnetosphere detected from the ground-based measurements

    Energy Technology Data Exchange (ETDEWEB)

    Stepanova, Marina [Physical Department, Universidad de Santiago de Chile (Chile); Foppiano, Alberto; Ovalle, Elias [Departmento de Geofisica, Universidad de Conception (Chile); Antonova, Elizavieta [Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow (Russian Federation); Troshichev, Oleg [Department of Geophysics, Arctic and Antarctic Research Institute, St. Petersburg (Russian Federation)], E-mail: mstepano@usach.cl

    2008-11-01

    Turbulent processes in the Earth's magnetosphere are reflected in the dynamical behavior of the geomagnetic indices and other parameters determined from ground based observations. Intermittent properties of one minute Polar Cap (PC) index and auroral radio wave absorption are studied using 1995-2000 data sets. It was found that the probability distribution functions (PDFs) of both PC-index and absorption fluctuations display a strong non-Gaussian shape. This indicates that they are not characterized by a global time self-similarity but rather exhibit intermittency, as previously reported for solar wind velocity and auroral electrojet index values. In the case of the auroral absorption it was also found that intermittency strongly depends on the magnetic local time, being largest in the nighttime sector. This shows that the acceleration of precipitating particles is intermittent, especially near the substorm eye, where the level of turbulence increases. Application of the Local Intermittency Measure (LIM) technique confirms the aforementioned results to a better precision.

  2. Potential Structures and Particle Acceleration on Auroral Field Lines.

    Science.gov (United States)

    2014-09-26

    90245 It. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE Space Division 1 May 1985 Los Angeles Air Force Station 13. NUMBEROpt PAGES Los ,~glesCali...communications, lid&r, and electro- optics; cmmuniction sciences, applied electronics, semiconductor crystal and device physics, radiometric tmating

  3. On the ionospheric coupling of auroral electric fields

    Directory of Open Access Journals (Sweden)

    G. T. Marklund

    2009-04-01

    Full Text Available The quasi-static coupling of high-altitude potential structures and electric fields to the ionosphere is discussed with particular focus on the downward field-aligned current (FAC region. Results are presented from a preliminary analysis of a selection of electric field events observed by Cluster above the acceleration region. The degree of coupling is here estimated as the ratio between the magnetic field-aligned potential drop, ΔΦII, as inferred from the characteristic energy of upward ion (electron beams for the upward (downward current region and the high-altitude perpendicular (to B potential, ΔΦbot, as calculated by integrating the perpendicular electric field across the structure. For upward currents, the coupling can be expressed analytically, using the linear current-voltage relation, as outlined by Weimer et al. (1985. This gives a scale size dependent coupling where structures are coupled (decoupled above (below a critical scale size. For downward currents, the current-voltage relation is highly non-linear which complicates the understanding of how the coupling works. Results from this experimental study indicate that small-scale structures are decoupled, similar to small-scale structures in the upward current region. There are, however, exceptions to this rule as illustrated by Cluster results of small-scale intense electric fields, correlated with downward currents, indicating a perfect coupling between the ionosphere and Cluster altitude.

  4. An Infrared Spectral Radiance Code for the Auroral Thermosphere (AARC)

    Science.gov (United States)

    1987-11-24

    atmospheric scale height. 10. Read NFP, the number of escape function data points stored on the data file ALLDAT. 11. Read in tho values of SIGNO (I), for...I equal 1 to NPT, where SIGNO are the values of the cross section multiplied by the column den- sity for the set of values of the band transmission

  5. Cassini Imaging of Auroral Emissions on the Galilean Satellites

    Science.gov (United States)

    Geissler, P.; McEwen, A.; Porco, C.

    2001-05-01

    Cassini captured several sequences of images showing Io, Europa and Ganymede while the moons were eclipsed by Jupiter. Io was the best studied of the satellites, with 4 eclipses successfully recorded. Earlier eclipse imaging by Galileo (Geissler et al., Science 295, 870-874) had shown colorful atmospheric emissions from Io and raised questions concerning their temporal variability and the identity of the emitting species. With its high data rate and numerous filter combinations, Cassini was able to fill some of the gaps in our knowledge of Io's visible aurorae. Io's bright equatorial glows were detected at previously unknown wavelengths and were also seen in motion. One eclipse took place on 12/29/2000 while Io was far from the plasma torus center. The pair of equatorial glows near the sub-Jupiter and anti-Jupiter points appeared about equal in brightness and changed little in location or intensity over a two hour period. Io crossed the plasma torus center during the next eclipse on 1/01/2001, as it passed through System III magnetic longitudes from 250 to 303 degrees. The equatorial glows were seen to shift in latitude during this eclipse, tracking the tangent points of the jovian magnetic field lines. This behaviour is similar to that observed for ultraviolet and other atomic emissions, and confirms that these visible glows are powered by Birkeland currents connecting Io and Jupiter. The eclipse on 1/05/2001 provided the best spectral measurements of the aurorae. The equatorial glows were detected at near ultraviolet wavelengths, consistent with their interpretation as molecular SO2 emissions. More than 100 kR were recorded in the ISS UV3 filter (300-380 nm) along with a similar intensity in BL1 (290-500 nm), comparable to Galileo estimates. At least 50 kR were detected in UV2 images (265-330 nm). No detection was made in UV1 (235-280 nm), allowing us to place an upper limit of about 100 kR. A new detection of the equatorial glows was made in the IR1 band (670-850 nm), possibly due to singly ionized oxygen ([OII] 732,733 nm). Limb glows distinct from the equatorial emissions were detected in the CB1 (595-645 nm) and RED (570-730) filters, consistent with [OI] 630,636 nm emissions. A small "knot" or concentration of emission near the north pole of Io was seen in all three eclipses, probably caused by a plume erupting from the volcano Tvashtar (McEwen et al., this meeting). Ganymede and Europa were detected in eclipses on 1/10 and 1/11/2001. Results of preliminary analyses will be presented.

  6. Quadrant photometer for satellite-borne auroral and optical measurements.

    Science.gov (United States)

    Criswell, D R; O'Brien, B J

    1967-06-01

    A multichannel photometer has been developed for space applications requiring low weight and power, no moving parts, and high sensitivity. The photocathode of a special phototube is divided into four electrically and optically distinct quadrants. The system operates without degradation after exposure to full sunlight, and has a sensitivity down to the order of rayleighs (10(6) photons cm(-2) sec(-1)). The complete photometer, including high voltage and control circuitry and signal conditioning with A/D converter and three lenses and interference filters, has a weight of 1.7 kg, power consumption of less than 0.3 W, and switching speeds up to 30 cycles/sec. These are to be compared with a previous multichannel photometer with a moving filter wheel, whose corresponding characteristics were 9 kg, 7-9 W, and 0.1 cycles/sec.

  7. Infrared Interferometry of Auroral Ionosphere-Thermosphere Energetics Project

    Data.gov (United States)

    National Aeronautics and Space Administration —  The FWMI prototype development is underway at USU/SDL. To develop the FWMI, USU/SDL is leveraging the successful implementation of a rocket-borne Michelson...

  8. The auroral O+ non-Maxwellian velocity distribution function revisited

    Directory of Open Access Journals (Sweden)

    F. Leblanc

    Full Text Available New characteristics of O+ ion velocity distribution functions in a background of atomic oxygen neutrals subjected to intense external electromagnetic forces are presented. The one dimensional (1-D distribution function along the magnetic field displays a core-halo shape which can be accurately fitted by a two Maxwellian model. The Maxwellian shape of the 1-D distribution function around a polar angle of 21 ± 1° from the magnetic field direction is confirmed, taking into account the accuracy of the Monte Carlo simulations. For the first time, the transition of the O+ 1-D distribution function from a core halo shape along the magnetic field direction to the well-known toroidal shape at large polar angles, through the Maxwellian shape at polar angle of 21 ± 1° is properly explained from a generic functional of the velocity moments at order 2 and 4.

  9. Aspects of magnetosphere-ionosphere coupling in sawtooth substorms: a case study

    Science.gov (United States)

    Sandholt, P. E.; Farrugia, C. J.

    2014-10-01

    In a case study we report on repetitive substorm activity during storm time which was excited during Earth passage of an interplanetary coronal mass ejection (ICME) on 18 August 2003. Applying a combination of magnetosphere and ground observations during a favourable multi-spacecraft configuration in the plasma sheet (GOES-10 at geostationary altitude) and in the tail lobes (Geotail and Cluster-1), we monitor the temporal-spatial evolution of basic elements of the substorm current system. Emphasis is placed on activations of the large-scale substorm current wedge (SCW), spanning the 21:00-03:00 MLT sector of the near-Earth plasma sheet (GOES-10 data during the interval 06:00-12:00 UT), and magnetic perturbations in the tail lobes in relation to ground observations of auroral electrojets and convection in the polar cap ionosphere. The joint ground-satellite observations are interpreted in terms of sequential intensifications and expansions of the outer and inner current loops of the SCW and their respective associations with the westward electrojet centred near midnight (24:00 MLT) and the eastward electrojet observed at 14:00-15:00 MLT. Combined magnetic field observations across the tail lobe from Cluster and Geotail allow us to make estimates of enhancements of the cross-polar-cap potential (CPCP) amounting to ≈ 30-60 kV (lower limits), corresponding to monotonic increases of the PCN index by 1.5 to 3 mV m-1 from inductive electric field coupling in the magnetosphere-ionosphere (M-I) system during the initial transient phase of the substorm expansion.

  10. Antarctic atmospheric infrasound. Final technical report, 1 July 1981-30 September 1984

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, C.R.; McKibben, B.N.

    1986-11-01

    In order to monitor atmospheric infrasonic waves in the passband from 0.1 to 0.01 Hz a digital infrasonic detection system was installed in Antarctica on the Ross Ice shelf near McMurdo Station on McMurdo Sound. An array of seven infrasonic microphones subtending an area of about 35 sg km was operated in Windless Bight. The analog microphone data were telemetered to McMurdo station where the infrasonic date were digitized and subjected to on-line real-time analysis to detect traveling infrasonic waves with periods from 10 to 100 seconds. During the period of operation of the Antartic infrasonic observatory, hundreds of infrasonic signals were detected in association with many natural sources such as the aurora australis, marine storm sea-air interactions, volcanic eruptions, mountain generated lee-wave effects, large meteors and auroral electrojet supersonic motions.

  11. GPS phase scintillation at high latitudes during the geomagnetic storm of 17-18 March 2015

    DEFF Research Database (Denmark)

    Prikryl, P.; Ghoddousi-Fard, R.; Weygand, J. M.

    2016-01-01

    , and magnetometers. The phase scintillation index is computed for signals sampled at a rate of up to 100 Hz by specialized GPS scintillation receivers supplemented by the phase scintillation proxy index obtained from geodetic-quality GPS data sampled at 1 Hz. In the context of solar wind coupling...... the scintillation and auroral electrojet currents observed by arrays of ground-based magnetometers as well as energetic particle precipitation observed by the DMSP satellites. Equivalent ionospheric currents are obtained from ground magnetometer data using the spherical elementary currents systems technique...... of energetic electron precipitation observed by DMSP satellites with the exception of a period of pulsating aurora when only very weak currents were observed....

  12. Elements of M-I Coupling in Repetitive Substorm Activity Driven by Interplanetary CMEs

    Science.gov (United States)

    Farrugia, C. J.; Sandholt, P. E.

    2014-12-01

    By means of case studies we explore key elements of the magnetosphere-ionosphere current system associated with repetitive substorm activity during persistent strong forcing by ICMEs. Our approach consists of a combination of the magnetospheric and ionospheric perspectives on the substorm activity. The first aspect is the near-Earth plasma sheet with its repetitive excitations of the substorm current wedge, as monitored by spacecraft GOES-10 when it traversed the 2100-0300 MLT sector, and its coupling to the westward auroral electrojet (WEJ) centered near midnight during the stable interplanetary (IP) conditions. The second aspect is the excitation of Bostrom type II currents maximizing at dusk and dawn and their associated ionospheric Pedersen current closure giving rise to EEJ (WEJ) events at dusk (dawn). As documented in our study, this aspect is related to the braking phase of Earthward-moving dipolarization fronts-bursty bulk flows. We follow the magnetospheric flow/field events from spacecraft Geotail in the midtail (X = - 11 Re) lobe to geostationary altitude at pre-dawn MLTs (GOES 10). The associated M-I coupling is obtained from ground-satellite conjunctions across the double auroral oval configuration along the meridian at dusk. By this technique we distinguish between ionospheric manifestations in three latitude regimes: (i) auroral oval south, (ii) auroral oval north, and (iii) polar cap. Regime (iii) is characterized by events of enhanced antisunward convection near the polar cap boundary (flow channel events) and in the central polar cap (PCN-index events). The repetitive substorm activity is discussed in the context of the level of IP driving as given by the geoeffective IP electric field (E_KL), magnetotail reconnection (inferred from the PCN-index and spacecraft Wind at X = - 77 Re) and the storm SYM-H index. We distinguish between different variants of the repetitive substorm activity, giving rise to electrojet (AL)-plasma convection (PCN) events

  13. On the dynamics of large-scale traveling ionospheric disturbances over Europe on 20 November 2003

    Science.gov (United States)

    Borries, Claudia; Jakowski, Norbert; Kauristie, Kirsti; Amm, Olaf; Mielich, Jens; Kouba, Daniel

    2017-01-01

    Ionospheric disturbances, often associated with geomagnetic storms, may cause threats to radio systems used for communication and navigation. One example is the super storm on 20 November 2003, when plenty of strong and unusual perturbations were reported. This paper reveals additional information on the dynamics in the high-latitude ionosphere over Europe during this storm. Here analyses of wavelike traveling ionospheric disturbances (TIDs) over Europe are presented, based on estimates of the total electron content (TEC) derived from ground-based Global Navigation Satellite System (GNSS) measurements. These TIDs are ionospheric signatures of thermospheric surges initiated by space weather events. The source region of these TIDs is characterized by enhanced spatial gradients, TEC depression, strong uplift of the F2 layer, the vicinity of the eastward auroral electrojet, and strong aurora E layers. Joule heating is identified as the most probable driver for the TIDs observed over Europe during 20 November 2003. The sudden heating of the thermosphere leads to strong changes in the pressure and thermospheric wind circulation system, which in turn generates thermospheric wind surges observed as TID signatures in the TEC. Either the dissipation of the eastward auroral electrojet or particle precipitation are considered as the source mechanism for the Joule heating. In the course of the storm, the TEC observations show a southward shift of the source region of the TIDs. These meridional dislocation effects are obviously related to a strong compression of the plasmasphere. The presented results demonstrate the complex interaction processes in the thermosphere-ionosphere-magnetosphere system during this extreme storm.

  14. The electric field response to the growth phase and expansion phase onset of a small isolated substorm

    Directory of Open Access Journals (Sweden)

    R. V. Lewis

    Full Text Available We capitalise on the very large field of view of the Halley HF radar to provide a comprehensive description of the electric field response to the substorm growth phase and expansion phase onset of a relatively simple isolated substorm ( |AL| < 250 nT which occurred on 13 June 1988. The substorm phases are identified by their standard ground magnetic and spacecraft energetic particle signatures, which provide a framework for the radar measurements. The substorm is preceded by a prolonged period (>12 h of magnetic quiescence, such that prior to the start of the growth phase, the apparent latitudinal motion of the radar backscatter returns is consistent with the variation in latitude of the quiet-time auroral oval with magnetic local time. The growth phase is characterised by an increasing, superimposed equatorward motion of the equatorward edge of the radar backscatter as the auroral oval expands. Within this backscatter region, there is a poleward gradient in the Doppler spectral width, which we believe to correspond to latitudinal structure in auroral emissions and magnetospheric precipitation. During the growth phase the ionospheric convection is dominated by a relatively smooth large-scale flow pattern consistent with the expanding DP2 (convection auroral electrojets. Immediately prior to substorm onset the ionospheric convection observed by the radar in the midnight sector has a predominantly equatorward flow component. At substorm onset a dramatic change occurs and a poleward flow component prevails. The timing and location are quite remarkable. The timing of the flow change is within one minute of the dispersionless injection observed at geostationary orbit and the Pi2 magnetic signature on the ground. The location shows that this sudden change in flow is due to the effect of the upward field aligned current of the substorm current wedge imposed directly within the Halley radar field of view.

  15. GENERATION OF EXTREMELY LOW FREQUENCY WAVES BY MODULATED HEATING OF POLAR IONOSPHERIC F REGION%极区电离层F区加热激发极低频波研究

    Institute of Scientific and Technical Information of China (English)

    徐彤; 徐彬; 吴健; 胡艳莉; 许正文

    2014-01-01

    Polar ionospheric heaters operated by HARRP and EISCAT have generated extremely low frequency waves by modulating the auroral electrojet at D and E region altitudes .However , the auroral electrojet often varies over time and is not always present .Alternatively, modulated F-region HF heating can generate ionospheric diamagnetic cur-rent, and the periodic modulation results in a magnetic moment that radiates extremely low frequency waves .Based on a one-dimensional time physical model of polar ionospheric heating and a full-wave model , we analyzed the fea-tures of extremely low frequency waves over Tromsø(69.59°N, 19.23°E).The results showed that extremely low frequency waves on the ground are different from lower ionospheric modulation , i.e., radiation of polar electrojet antenna.Furthermore, effective radiated power (ERP), modulated frequency, and ionospheric background, have significant influence on the generated extremely low frequency wave .%“极区电急流天线”辐射依赖于低电离层D/E区背景电急流,而高电离层F区极低频调制加热,可产生抗磁性电流,形成极低频波辐射源。利用电离层F区一维时变加热数值模型,采用全波解算法研究高纬Tromsø(69.59°N,19.23°E)地区电离层F区极低频调制加热。模拟结果表明,极区高电离层激发的极低频波与极区低电离层激发的结果不同。加热泵波的有效辐射功率( effective radiated power ,ERP)、调制频率及电离层背景对极低频波强度有着重要影响。

  16. Storm induced large scale TIDs observed in GPS derived TEC

    Directory of Open Access Journals (Sweden)

    C. Borries

    2009-04-01

    Full Text Available This work is a first statistical analysis of large scale traveling ionospheric disturbances (LSTID in Europe using total electron content (TEC data derived from GNSS measurements. The GNSS receiver network in Europe is dense enough to map the ionospheric perturbation TEC with high horizontal resolution. The derived perturbation TEC maps are analysed studying the effect of space weather events on the ionosphere over Europe.

    Equatorward propagating storm induced wave packets have been identified during several geomagnetic storms. Characteristic parameters such as velocity, wavelength and direction were estimated from the perturbation TEC maps. Showing a mean wavelength of 2000 km, a mean period of 59 min and a phase speed of 684 ms−1 in average, the perturbations are allocated to LSTID. The comparison to LSTID observed over Japan shows an equal wavelength but a considerably faster phase speed. This might be attributed to the differences in the distance to the auroral region or inclination/declination of the geomagnetic field lines.

    The observed correlation between the LSTID amplitudes and the Auroral Electrojet (AE indicates that most of the wave like perturbations are exited by Joule heating. Particle precipitation effects could not be separated.

  17. Ionospheric electron density perturbations during the 7-10 March 2012 geomagnetic storm period

    Science.gov (United States)

    Belehaki, Anna; Kutiev, Ivan; Marinov, Pencho; Tsagouri, Ioanna; Koutroumbas, Kostas; Elias, Panagiotis

    2017-02-01

    From 7 to 10 March 2012 a series of magnetospheric disturbances caused perturbations in the ionospheric electron density. Analyzing the interplanetary causes in each phase of this disturbed period, in comparison with the total electron content (TEC) disturbances, we have concluded that the interplanetary solar wind controls largely the ionospheric response. An interplanetary shock detected at 0328UT on 7 March caused the formation of prompt penetrating electric fields in the dayside that transported plasma from the near-equatorial region to higher in attitudes and latitudes forming a giant plasma fountain which is part of the so-called dayside ionospheric super-fountain. The super-fountain produces an increase in TEC which is the dominant effect at middle latitude, masking the effect of the negative storm. Simultaneously, inspecting the TEC maps, we found evidence for a turbulence in TEC propagating southward probably caused by large scale travelling ionospheric disturbances (LSTIDs) linked to auroral electrojet intensification. On 8 March, a magnetospheric sudden impulse at 1130UT accompanied with strong pulsations in all interplanetary magnetic field (IMF) components and with northward Bz component during the growth phase of the storm. These conditions triggered a pronounced directly driven substorm phase during which we observe LSTID. However, the analysis of DMSP satellite observations, provided with strong evidence for Sub-Auroral Polarization Streams (SAPS) formation that erode travelling ionospheric disturbances (TID) signatures. The overall result of these mechanisms can be detected in maps of de-trended TEC, but it is difficult to identify separately each of the sources of the observed perturbations, i.e. auroral electrojet activity and LSTIDs, super-fountain and SAPS. In order to assess the capability of the ionospheric profiler called Topside Sounder Model - assisted Digisonde (TaD model) to detect such perturbations in the electron density, electron

  18. A Study of Single and Multiple Onset Substorms

    Science.gov (United States)

    Larson, R. B.; Stoner, J. M.; Erickson, K. N.; Engebretson, M. J.; Scudder, J. D.; Frey, H. U.; Russell, C. T.

    2007-12-01

    A good indicator of substorm expansion phase onset is a well-defined increase and/or energization of the HYDRA electron flux measured onboard POLAR when the satellite is on the night side in the central region of the near earth plasmasheet. This signature is usually, but not always, accompanied by a dipolarization of the magnetic field. Another clear indicator of expansion phase onset is a well-defined increase in the z-component of the magnetic field which is indicative of dipolarization on the night side at geostationary orbit. Substorm events for this study were selected using these two indicators. 34 expansion phase onsets were found using the HYDRA instrument and 119 onsets were found using GOES 10 satellite data. For event selection the GSM coordinates of POLAR were constrained as follows: -9 < x < -7, -2 < y < 2, -1 < z < 1 in units of earth radii. The GOES 10 location was subject to the requirement that the satellite was located within 3 hours either side of local midnight. As expected these onset times were found to be closely correlated with the onset of ground-based auroral zone enhanced Pi2 activity and magnetic bays. Multiple onset substorms were distinguished from single onset events by observing the occurrence of one or more additional subsequent Pi2 intensifications and negative bays corresponding to enhancements of the westward electrojet. For several events, when data was available, auroral brightenings at the equatorward edge of discrete arcs as observed by the FUV experiment onboard the IMAGE spacecraft were also found to be closely correlated with not only the initial Pi2 intensification but also with subsequent Pi2 intensifications. The ratio of multiple onset to single onset substorms was found to be 2.3:1. Using Pi2 and IMAGE FUV data it was found that the initial onset of a multiple onset substorm usually corresponds to Pi2 intensifications and auroral brightening signatures at a lower auroral zone latitude than for a single onset event. In

  19. Brightening of onset arc precedes the dipolarization onset: THEMIS observations of two events on 1 March 2008

    Science.gov (United States)

    Kan, J. R.; Li, H.; Wang, C.; Frey, H. U.; Kubyshkina, M. V.; Runov, A.; Xiao, C. J.; Lyu, L. H.; Sun, W.

    2011-11-01

    We present a new M-I coupling model of substorm during southward IMF based on the THEMIS observations of two events on 1 March 2008. The first event (E-1) was classified as a pseudo-breakup: brightening of the onset arc preceded the first dipolarization onset by ∼71 ± 3 s, but the breakup arcs faded within ∼5 min without substantial poleward expansion and the dipolarization stopped and reversed to thinning. The second event (E-2) was identified as a substorm: brightening of the second onset arc preceded the second dipolarization onset by ∼80 ± 3 s, leading to a full-scale expanding auroral bulge during the substorm expansion phase for ∼20 min. The Alfvén travel time from the ionosphere to the dipolarization onset region is estimated at ∼69.3 s in E-1; at ∼80.3 s in E-2, which matched well with the observed time delay of the dipolarization onset after the brightening of the onset arc, respectively in E-1 and E-2. Brightening of the onset arc precedes the dipolarization onset suggest that the onset arc brightening is caused by the intense upward field-aligned currents originating from the divergence of the Cowling electrojet in the ionosphere. The Cowling electrojet current loop (CECL) is formed to close the field-aligned currents at all times. The closure current in the Alfvén wavefront is anti-parallel to the cross-tail current. Dipolarization onset occurs when the Alfvén wavefront incident on the near-Earth plasma sheet to disrupt the cross-tail current in the dipolarization region. Slow MHD waves dominate the disruption of the cross-tail current in the dipolarization region.

  20. Brightening of onset arc precedes the dipolarization onset: THEMIS observations of two events on 1 March 2008

    Directory of Open Access Journals (Sweden)

    J. R. Kan

    2011-11-01

    Full Text Available We present a new M-I coupling model of substorm during southward IMF based on the THEMIS observations of two events on 1 March 2008. The first event (E-1 was classified as a pseudo-breakup: brightening of the onset arc preceded the first dipolarization onset by ∼71 ± 3 s, but the breakup arcs faded within ∼5 min without substantial poleward expansion and the dipolarization stopped and reversed to thinning. The second event (E-2 was identified as a substorm: brightening of the second onset arc preceded the second dipolarization onset by ∼80 ± 3 s, leading to a full-scale expanding auroral bulge during the substorm expansion phase for ∼20 min. The Alfvén travel time from the ionosphere to the dipolarization onset region is estimated at ∼69.3 s in E-1; at ∼80.3 s in E-2, which matched well with the observed time delay of the dipolarization onset after the brightening of the onset arc, respectively in E-1 and E-2. Brightening of the onset arc precedes the dipolarization onset suggest that the onset arc brightening is caused by the intense upward field-aligned currents originating from the divergence of the Cowling electrojet in the ionosphere. The Cowling electrojet current loop (CECL is formed to close the field-aligned currents at all times. The closure current in the Alfvén wavefront is anti-parallel to the cross-tail current. Dipolarization onset occurs when the Alfvén wavefront incident on the near-Earth plasma sheet to disrupt the cross-tail current in the dipolarization region. Slow MHD waves dominate the disruption of the cross-tail current in the dipolarization region.

  1. Energy density of ionospheric and solar wind origin ions in the near-Earth magnetotail during substorms

    Science.gov (United States)

    Daglis, Loannis A.; Livi, Stefano; Sarris, Emmanuel T.; Wilken, Berend

    1994-01-01

    Comprehensive energy density studies provide an important measure of the participation of various sources in energization processes and have been relatively rare in the literature. We present a statistical study of the energy density of the near-Earth magnetotail major ions (H(+), O(+), He(++), He(+)) during substorm expansion phase and discuss its implications for the solar wind/magnetosphere/ionosphere coupling. Our aim is to examine the relation between auroral activity and the particle energization during substorms through the correlation between the AE indices and the energy density of the major magnetospheric ions. The data we used here were collected by the charge-energy-mass (CHEM) spectrometer on board the Active Magnetospheric Particle Trace Explorer (AMPTE)/Charge Composition Explorer (CCE) satellite in the near-equatorial nightside magnetosphere, at geocentric distances approximately 7 to 9 R(sub E). CHEM provided the opportunity to conduct the first statistical study of energy density in the near-Earth magnetotail with multispecies particle data extending into the higher energy range (greater than or equal to 20 keV/E). the use of 1-min AE indices in this study should be emphasized, as the use (in previous statistical studies) of the (3-hour) Kp index or of long-time averages of AE indices essentially smoothed out all the information on substorms. Most distinct feature of our study is the excellent correlation of O(+) energy density with the AE index, in contrast with the remarkably poor He(++) energy density - AE index correlation. Furthermore, we examined the relation of the ion energy density to the electrojet activity during substorm growth phase. The O(+) energy density is strongly correlated with the pre-onset AU index, that is the eastward electrojet intensity, which represents the growth phase current system. Our investigation shows that the near-Earth magnetotail is increasingly fed with energetic ionospheric ions during periods of enhanced

  2. Application of electromagnetic-wave-ionospheric interactions to global warming in the arctic region

    Science.gov (United States)

    Wong, A. Y.

    An approach to expel pollutants which can contribute to global warming from the upper atmosphere by the use of HF electromagnetic waves has been proposed [1]. Laboratory plasma experiments have shown that significant gyro-resonance acceleration of minority ion species in a plasma is possible. The separation of ions differing in mass by one unit has been achieved. This method is applicable to the selective acceleration of ions perpendicular to the geomagnetic field in the ionosphere and involves the modulation of the auroral electrojet current to excite ion cyclotron waves. On account of the divergent geomagnetic field in the polar atmosphere the accelerated perpendicular ion velocity is converted into an upward motion along open magnetic field lines. The ions thus removed will not return to the upper atmosphere. Negatively charged particles move upward by the fair-weather electric field and by atmospheric convection. When ions reach above 120˜ km altitude where the ion gyro-frequency is comparable to or greater than the ion-neutral collision frequency, they can be accelerated by electromagnetic fields through the gyro-resonance interaction. By modulating the auroral electrojet in the gyro-frequency range for important minority ion species (˜ 15--30 Hz for CO2-, and Cl-) electromagnetic ion cyclotron waves can be excited, which propagate nearly along the geomagnetic field lines. Experimental evidence for this effect has been obtained with the HIPAS facility [Wong et al., 1997]. When exciting ELF waves over a range of ion gyro-frequencies of dominant ion species, dips were observed in magnetometer data at ion gyro-frequencies of various species, which suggests that the ELF wave energy was absorbed by ions. Similar ion acceleration and expelling phenomenon over the polar regions occurs naturally in so called ion conics as observed by high latitude satellites. Field aligned currents might provide the free energy needed to make this process practical. Field

  3. SABRE observations of Pi2 pulsations: case studies

    Science.gov (United States)

    Bradshaw, E. G.; Lester, M.

    1997-01-01

    The characteristics of substorm-associated Pi2 pulsations observed by the SABRE coherent radar system during three separate case studies are presented. The SABRE field of view is well positioned to observe the differences between the auroral zone pulsation signature and that observed at mid-latitudes. During the first case study the SABRE field of view is initially in the eastward electrojet, equatorward and to the west of the substorm-enhanced electrojet current. As the interval progresses, the western, upward field-aligned current of the substorm current wedge moves westward across the longitudes of the radar field of view. The westward motion of the wedge is apparent in the spatial and temporal signatures of the associated Pi2 pulsation spectra and polarisation sense. During the second case study, the complex field-aligned and ionospheric currents associated with the pulsation generation region move equatorward into the SABRE field of view and then poleward out of it again after the third pulsation in the series. The spectral content of the four pulsations during the interval indicate different auroral zone and mid-latitude signatures. The final case study is from a period of low magnetic activity when SABRE observes a Pi2 pulsation signature from regions equatorward of the enhanced substorm currents. There is an apparent mode change between the signature observed by SABRE in the ionosphere and that on the ground by magnetometers at latitudes slightly equatorward of the radar field of view. The observations are discussed in terms of published theories of the generation mechanisms for this type of pulsation. Different signatures are observed by SABRE depending on the level of magnetic activity and the position of the SABRE field of view relative to the pulsation generation region. A twin source model for Pi2 pulsation generation provides the clearest explanation of the signatures observed Acknowledgements. The authors are grateful to Prof. D. J. Southwood

  4. Studies of the auroral zone ionosphere using the MITHRAS data base, fiscal years 1983-1985

    Science.gov (United States)

    1986-06-01

    The Autospheric Science group participated in the multi-radar MITHRAS experimental campaign. Coordinated observations of the Earth's ionosphere, magnetosphere, and thermosphere were conducted using the Millstone Hill, Massachusetts, Chatanika, Alaska, and European EISCAT incoherent scatter radars in conjunction with a variety of ground based and satellite experiments. Chatanika and EISCAT are about 11 hours apart in magnetic local time, and Millstone Hill precedes Chatanika and follows EISCAT by more than 6 hours. Each of the three radars was able to study aruroal zone latitudes, but at widely spaced longitudes. Hence the MITHRAS program was well suited to study the class of problems which involve universal time/local time ambiguities, or equivalenty, space/time differences. Set operating modes were used at the radar sites to best match the requirements of the several campaign objectives. The overall MITHRAS program was motivated by a desire to provide a well documented set of radar observations of the mid and high latitude ionosphere during the brief interval when three incoherent scatter facilities would be available. At Millstone Hill the MITHRAS program involved the development of specific radar operating modes and analysis techniques appropriate for multi-instrument studies. An extensive data set resulted from the campaign.

  5. The Effects of Magnetic Storm Phases on F-Layer Irregularities from Auroral to Equatorial Lattitudes.

    Science.gov (United States)

    2007-11-02

    Radar data from Jicamarca, Peru and phase fluctuation data from Arequipa , Santiago and Kourou were used to study the occurrence and intensity of...overhead field line at the radar site at Jicamarca and the overhead field line at Arequipa . At times thin layers were shown on the radar but plumes

  6. What are the mechanisms that produce auroral asymmetries in the conjugate hemispheres? (Invited)

    Science.gov (United States)

    Ostgaard, N.; Reistad, J. P.; Tenfjord, P.; Laundal, K.

    2013-12-01

    Our knowledge about how the Earth is coupled to space is to a large extent based on measurements from only one polar hemisphere. It is therefore tempting to assume that the aurora borealis (northern hemisphere) and aurora australis (southern hemisphere) are mirror images of each other because the charged particles producing the aurora follow the magnetic field lines connecting the two hemispheres. There are now many observational evidence that this is not always the case. By studying simultaneous global imaging in the ultraviolet wavelengths by the IMAGE and Polar satellites we have shown that the northern and southern aurora can be asymmetric both in locations and intensities. To explain these findings three mechanisms have been suggested: 1) difference in region 1 currents due to hemispheric differences in the solar wind dynamo efficiency when the IMF has a significant Bx component 2) interhemispheric currents associated with the penetration of the IMF By component into the closed magnetosphere. 3) interhemispheric currents due to conductivity differences in the two hemispheres We will present simultaneous conjugate images by IMAGE and Polar of event cases with asymmetries both in location and intensity. We have also used large data sets of imaging data and Cluster magnetic data to test whether the predicted effects of the three mechanisms of generating interhemispheric or asymmetric currents are statistically significant. Three mechanism that can produce asymmetric aurora: 1) Difference in solar wind dynamo due to an IMF Bx component, 2) Induced interhemispheric currents due to the non-uniform penetration of IMF By into the closed magnetosphere, and 3) Interhemispheric currents due to conductivity differences in the conjugate hemispheres.

  7. Sub-Auroral Ion Drifts as a Source of Mid-Latitude Plasma Density Irregularities

    Science.gov (United States)

    Sotnikov, V.; Kim, T.; Mishin, E.; Paraschiv, I.; Rose, D.

    Ionospheric irregularities cause scintillations of electromagnetic signals that can severely affect navigation and transionospheric communication, in particular during space storms. At midlatitudes, such space weather events are caused mainly by subauroral electric field structures (SAID/SAPS) [1, 2]. SAID/SAPS -related shear flows and plasma density troughs point to interchange and Kelvin-Helmholtz type instabilities as a possible source of plasma irregularities. A model of nonlinear development of these instabilities based on the two-fluid hydrodynamic description with inclusion of finite Larmor radius effects will be presented. A numerical code in C language to solve the derived nonlinear equations for analysis of interchange and flow velocity shear instabilities in the ionosphere was developed. This code was used to analyze competition between interchange and Kelvin Helmholtz instabilities in the equatorial region [3]. The high-resolution simulations with continuous density and velocity profiles will be driven by the ambient conditions corresponding to the in situ Defence Military Satellite Program (DMSP) satellite low-resolution data [2] during UHF/GPS L-band subauroral scintillation events. [1] Mishin, E. (2013), Interaction of substorm injections with the subauroral geospace: 1. Multispacecraft observations of SAID, J. Geophys. Res. Space Phys., 118, 5782-5796, doi:10.1002/jgra.50548. [2] Mishin, E., and N. Blaunstein (2008), Irregularities within subauroral polarization stream-related troughs and GPS radio interference at midlatitudes. In: T. Fuller-Rowell et al. (eds), AGU Geophysical Monograph 181, MidLatitude Ionospheric Dynamics and Disturbances, pp. 291-295, doi:10.1029/181GM26, Washington, DC, USA. [3] V. Sotnikov, T. Kim, E. Mishin, T. Genoni, D. Rose, I. Paraschiv, Development of a Flow Velocity Shear Instability in the Presence of Finite Larmor Radius Effects, AGU Fall Meeting, San Francisco, 15 - 19 December, 2014.

  8. Low-Resource CubeSat-scale Sensorcraft for Auroral and Ionospheric Plasma Studies

    OpenAIRE

    2010-01-01

    Explicitly separating variations in space from variations in time over a large volume is a current unmet challenge for in situ studies of the ionosphere and aurora. We propose that arrays of many (_ 10) low-resource sensorcraft can address this scientific and technical challenge. We are developing a suborbital CubeSat, RocketCube, to enable low-cost multipoint measurements for orbital and sub-orbital scientific missions. The graduate student-designed RocketCube showcases a new scientific inst...

  9. Global effect of auroral particle and Joule heating in the undisturbed thermosphere

    Science.gov (United States)

    Hinton, B. B.

    1978-01-01

    From the compositional variations observed with the neutral atmosphere composition experiment on OGO 6 and a simplified model of thermospheric dynamics, global average values of non-EUV heating are deduced. These are 0.19-0.25 mW/sq m for quiet days and 0.44-0.58 mW/sq m for ordinary days.

  10. La teoria di Halley sul magnetismo terrestre e sulle aurore polari.

    Science.gov (United States)

    D'Amico, S.

    1999-10-01

    This paper contains a brief description of some theories developed by Edmund Halley during the last years of the 17th century and the beginning of the 18th. This theories tried to explain the origin of terrestrial magnetism and its changes during the time, and gives a description of how magnetic force by the Earth could influence polar aurorae.

  11. Polarisation in the auroral red line during coordinated EISCAT Svalbard Radar/optical experiments

    Directory of Open Access Journals (Sweden)

    M. Barthélémy

    2011-06-01

    Full Text Available The polarisation of the atomic oxygen red line in the Earth's thermosphere is observed in different configurations with respect to the magnetic field line at high latitude during several coordinated Incoherent Scatter radar/optical experiment campaigns. When pointing northward with a line-of-sight nearly perpendicular to the magnetic field, we show that, as expected, the polarisation is due to precipitated electrons with characteristic energies of a few hundreds of electron Volts. When pointing toward the zenith or southward with a line-of-sight more parallel to the magnetic field, we show that the polarisation practically disappears. This confirms experimentally the predictions deduced from the recent discovery of the red line polarisation. We show that the polarisation direction is parallel to the magnetic field line during geomagnetic activity intensification and that these results are in agreement with theoretical work.

  12. Ionosphere dynamics in the auroral zone during the magnetic storm of March 17-18, 2015

    Science.gov (United States)

    Blagoveshchensky, D. V.; Sergeeva, M. A.

    2016-11-01

    A comprehensive study of the ionospheric processes encountered during the superstorm which started on March 17th 2015 has been carried out using magnetometer, ionosonde, riometer, ionospheric tomography and an all-sky camera installed in the observatory of Sodankylä, Finland. The storm manifested a number of interesting features. From 12:00 on March 17 there was a significant decrease of critical frequencies foF2 and intensive sporadic Es layers were observed. During the disturbance, there was a lack of variation of the X-component of the magnetic field at times, but the absorption level measured by the riometer was high. A comparison of the electron density distributions for the quiet and disturbed days as shown in the tomography data were very different. Where results were available at the same times, the tomographic foF2 values coincided with the "real" foF2 values from the ionosonde. Where the ionosonde data was missing due to absorption, the tomographic foF2 values were used instead. The keograms from the all-sky camera showed that during disturbed days the aurorae manifested themselves as bright discrete forms. It was shown that the peaks of absorption due to particle precipitation seen by the riometer coincided in time with the brightenings of aurorae seen on the keograms.

  13. Environmental Impact Statement. Volume 1. Proposed High Frequency Active Auroral Research Program

    Science.gov (United States)

    1993-07-01

    Picea mariana Bog blueberry Vaccinium Labrador tea Ledwn groenlandicum Sedges Cyperaceae Sphagnum moss Sphagnum sp. Tamarack Larix laricina White...of 25 to 60%. A wet herbaceous vegetation association occurs in wet areas with grasses and sedges and is analogous to Cowardin et al.’s (1979...wetlands dominated by sedges and rushes. Minimal amounts of palustrine aquatic bed are present. Forested wetlands (equivalent to palustrine forested

  14. A Coherent Nonlinear Theory of Auroral Kilometric Radiation. II. Dynamic Interactions.

    Science.gov (United States)

    1981-03-27

    Kennel Attn: Library F. Coronlti R. Sudan B. Kusse Columbia University H. Fleischmann New York, New York 10027 C. Wharton Attn: R. Taussig F. Morse R. A...Phoenix Corp. 20 Demar Road 1600 Anderson Road Lexington, Maryland 02173 McLean, Virginia 22102 Gendrin, Roger Schulz, Michael CNET Aerospace Corp. 3 Ave...Physics & Astronomy Observatoire University of Iowa D.A.F. G21GO Iowa City, Iowa 52242 Meudon, FRANCE Temerin, Michael Space Science Lab. Kikuchi, Hiroshi

  15. HF omnidirectional spectral CW auroral radar (HF-OSCAR) at very high latitude. Part 1: Technique

    Science.gov (United States)

    Olesen, J. K.; Jacobsen, K. E.; Stauning, P.; Henriksen, S.

    1983-12-01

    An HF system for studies of very high latitude ionospheric irregularities was described. Radio aurora from field-aligned E-region irregularities of the Slant E Condition type were discussed. The complete system combines an ionosonde, a 12 MHz pulse radar and a 12 MHz bistatic CW Doppler-range set-up. The two latter units use alternately a 360 deg rotating Yagi antenna. High precision oscillators secure the frequency stability of the Doppler system in which the received signal is mixed down to a center frequency of 500 Hz. The Doppler shift range is max + or - 500 Hz. The received signal is recorded in analog form on magnetic tape and may be monitored visually and audibly. Echo range of the CW Doppler signal is obtained by a 150 Hz amplitude modulation of the transmitted signal and phase comparison with the backscattered signal.

  16. Pitch angle scattering of diffuse auroral electrons by whistler mode waves

    Energy Technology Data Exchange (ETDEWEB)

    Villalon, E. [Northeastern Univ., Boston, MA (United States); Burke, W.J. [Hanscom Air Force Base, MA (United States)

    1995-10-01

    Resonant electron-whistler interactions in the plasma sheet are investigated as possible explanations of the nearly isotropic fluxes of low-energy electrons observed above the diffuse aurora. Whistler mode waves, propagating near the resonance cone with frequencies near or larger than half the equatorial electron cyclotron frequency, can interact with low-energy plasma sheet electrons. A Hamiltonian formulation is developed for test particles interacting with the coherent chorus emission spectra. The authors consider the second-order resonance condition which requires that inhomogeneities in the Earth`s magnetic field be compensated by a finite bandwidth of wave frequencies to maintain resonance for extended distances along field lines. These second-order interactions are very efficient in scattering the electrons toward the atmospheric loss cone. Numerical calculations are presented for the magnetic shell L=5.5 for wave amplitudes of {approximately}10{sup {minus}6} V/m, using different frequency and magnetospheric conditions. 34 refs., 7 figs.

  17. Structured waves near the plasma frequency observed in three auroral rocket flights

    Directory of Open Access Journals (Sweden)

    M. Samara

    2006-11-01

    Full Text Available We present observations of waves at and just above the plasma frequency (fpe from three high frequency electric field experiments on three recent rockets launched to altitudes of 300–900 km in active aurora. The predominant observed HF waves just above fpe are narrowband, short-lived emissions with amplitudes ranging from <1 mV/m to 20 mV/m, often associated with structured electron density. The nature of these HF waves, as determined from frequency-time spectrograms, is highly variable: in some cases, the frequency decreases monotonically with time as in the "HF-chirps" previously reported (McAdams and LaBelle, 1999, but in other cases rising frequencies are observed, or features which alternately rise and fall in frequency. They exhibit two timescales of amplitude variation: a short timescale, typically 50–100 ms, associated with individual discrete features, and a longer timescale associated with the general decrease in the amplitudes of the emissions as the rocket moves away from where the condition f~fpe holds. The latter timescale ranges from 0.6 to 6.0 s, corresponding to distances of 2–7 km, assuming the phenomenon to be stationary and using the rocket velocity to convert time to distance.

  18. Multi-scale auroral observations in Apatity: winter 2010–2011

    Directory of Open Access Journals (Sweden)

    B. V. Kozelov

    2012-03-01

    Full Text Available Routine observations of the aurora are conducted in Apatity by a set of five cameras: (i all-sky TV camera Watec WAT-902K (1/2"CCD with Fujinon lens YV2.2 × 1.4A-SA2; (ii two monochromatic cameras Guppy F-044B NIR (1/2"CCD with Fujinon HF25HA-1B (1:1.4/25 mm lens for 18° field of view and glass filter 558 nm; (iii two color cameras Guppy F-044C NIR (1/2"CCD with Fujinon DF6HA-1B (1:1.2/6 mm lens for 67° field of view. The observational complex is aimed at investigating spatial structure of the aurora, its scaling properties, and vertical distribution in the rayed forms. The cameras were installed on the main building of the Apatity division of the Polar Geophysical Institute and at the Apatity stratospheric range. The distance between these sites is nearly 4 km, so the identical monochromatic cameras can be used as a stereoscopic system. All cameras are accessible and operated remotely via Internet. For 2010–2011 winter season the equipment was upgraded by special blocks of GPS-time triggering, temperature control and motorized pan-tilt rotation mounts. This paper presents the equipment, samples of observed events and the web-site with access to available data previews.

  19. Near real-time geomagnetic data for space weather applications in the European sector

    Science.gov (United States)

    Johnsen, M. G.; Hansen, T. L.

    2012-12-01

    Tromsø Geophysical Observatory (TGO) is responsible for making and maintaining long time-series of geomagnetic measurements in Norway. TGO is currently operating 3 geomagnetic observatories and 11 variometer stations from southern Norway to Svalbard . Data from these 14 locations are acquired, processed and made available for the user community in near real-time. TGO is participating in several European Union (EU) and European Space Agency (ESA) space weather related projects where both near real-time data and derived products are provided. In addition the petroleum industry is benefiting from our real-time data services for directional drilling. Near real-time data from TGO is freely available for non-commercial purposes. TGO is exchanging data in near real-time with several institutions, enabling the presentation of near real-time geomagnetic data from more than 40 different locations in Fennoscandia and Greenland. The open exchange of non real-time geomagnetic data has been successfully going on for many years through services such as the world data center in Kyoto, SuperMAG, IMAGE and SPIDR. TGO's vision is to take this one step further and make the exchange of near real-time geomagnetic data equally available for the whole community. This presentation contains an overview of TGO, our activities and future aims. We will show how our near real-time data are presented. Our contribution to the space weather forecasting and nowcasting effort in the EU and ESA will be presented with emphasis on our real-time auroral activity index and brand new auroral activity monitor and electrojet tracker.

  20. Relation between substorm characteristics and rapid temporal variations of the ground magnetic field

    Directory of Open Access Journals (Sweden)

    A. Viljanen

    2006-03-01

    Full Text Available Auroral substorms are one of the major causes of large geomagnetically induced currents (GIC in technological systems. This study deals with different phases of the auroral substorm concerning their severity from the GIC viewpoint. Our database consists of 833 substorms observed by the IMAGE magnetometer network in 1997 (around sunspot minimum and 1999 (rising phase of the sunspot cycle, divided into two classes according to the Dst index: non-storm (Dst>-40 nT, 696 events and storm-time ones (Dst<-40 nT, 137 events. The key quantity concerning GIC is the time derivative of the horizontal magnetic field vector (dH/dt whose largest values during substorms occur most probably at about 5 min after the onset at stations with CGM latitude less than 72 deg. When looking at the median time of the occurrence of the maximum dH/dt after the expansion onset, it increases as a function of latitude from about 15 min at CGM lat=56 deg to about 45 min at CGM lat=75 deg for non-storm substorms. For storm-time events, these times are about 5 min longer. Based on calculated ionospheric equivalent currents, large dH/dt occur mostly during the substorm onset when the amplitude of the westward electrojet increases rapidly.

  1. Relationship between ionospheric electric fields and magnetic activity indices

    Science.gov (United States)

    Shirapov, D. Sh.

    2012-02-01

    The relations between electric fields in the daytime and nighttime sectors of the polar ionosphere and magnetic activity indices of auroral region (AL) and northern polar cap (PCN) are studied. It is found that the above relations do exist and are described by: a) equations U {pc/(1)} (kV) = 27.62 + 21.43PCN with a correlation coefficient R = 0.87 and U {pc/(1)} (kV) = 4.06 + 49.21PCN - 6.24 PCN2 between the difference in the electric potentials across the polar cap in the daytime sector U {pc/(1)} and PCN and b) regression equation U {pc/(2)} (kV) = 23.33 + 0.08|AL| with R = 0.86 between the difference in the electric potentials across the polar cap in the nighttime sector U {pc/(2)} and |AL|. It is shown that: a) it is possible to use the AL and PCN indices for real-time diagnostics of instantaneous values of the electric fields in the daytime and nighttime sectors of the polar ionosphere in the process of a substorm development; b) at the expansion phase of a substorm, due to calibration of PCN values by the values of the solar wind electric field E sw, the PCN index does not feel the contribution of the western electrojet and, accordingly, the contribution of the nighttime ionospheric electric field U {pc/(2)}, governed by the reconnection in the magnetospheric tail.

  2. Geoeffectiveness of Stream Interaction Regions during 2007-2008

    Science.gov (United States)

    Sanchez-Garcia, Elsa; Aguilar-Rodriguez, Ernesto; Ontiveros, Veronica

    2016-07-01

    The Stream Interaction Regions (SIRs) are generated in the interplanetary medium when a fast solar wind stream overtakes a slower one. If these large-scale phenomena interact with the Earth's magnetosphere they can give rise to geomagnetic storms (GSs). In this study we analyze the degree of geoeffectiveness of 20 events that were generated by SIRs. The events were observed during the 2007-2008 period that comprising the extended downward phase of solar cycle 23. The degree of geoeffectivity is measured using magnetic indices from different latitudes: PCN (Polar cap north), PCS (polar cap south), AA (antipodal amplitude), AE (Auroral Electrojet), Kp (estimated global index) and Dst (Disturbance storm time). We discuss some results on the correlation of these magnetic indices with the characteristics of shocks associated with the SIRs observed by STEREO-A/B, WIND and ACE spacecraft. All the 20 SIRs events generated GSs with Dst values in ranging from -86 nT up to -12 nT. Moreover, 6 out of the 20 events presented storm sudden commencement (SSC). We also discuss on the characteristics of the SIR-associated shocks and the intensity of the GSs.

  3. Solar wind - magnetosphere coupling efficiency during ejecta and sheath region driven geomagnetic storms

    Science.gov (United States)

    Myllys, Minna; Kilpua, Emilia; Lavraud, Benoit

    2016-04-01

    We have investigated the effect of key solar wind driving parameters on solar wind- magnetosphere coupling efficiency during sheath and magnetic cloud driven storms. The particular focus of the study was on the coupling efficiency dependence with Alfven Mach number (MA). The efficiency has been estimated using the dawn-dusk component of the interplanetary electric field (EY), Newell and Borovsky functions as a proxy for the energy inflow and the polar cap potential (PCN), auroral electrojet (AE) and SYM-H indices as the measure of the energy output. We have also performed a time delay analysis between the input parameters and the geomagnetic indices. We demonstrate that the PCN index distinctively shows both a MA dependent saturation and a MA-independent saturation, pointing to the existence of at least two underlying physical mechanisms for the saturation of the index. By contrast, we show that the AE index saturates, but that the saturation of this index is independent of the solar wind MA. Finally we find that the SYM-H index does not seem to saturate and that the absence of saturation is independent of the MA regime.

  4. Plasma and magnetic field variations in the distant magnetotail associated with near-earth substorm effects

    Science.gov (United States)

    Baker, D. N.; Bame, S. J.; Mccomas, D. J.; Zwickl, R. D.; Slavin, J. A.; Smith, E. J.

    1987-01-01

    Examination of many individual event periods in the ISEE 3 deep-tail data set has suggested that magnetospheric substorms produce a characteristic pattern of effects in the distant magnetotail. During the growth, or tail-energy-storage phase of substorms, the magnetotail appears to grow diametrically in size, often by many earth radii. Subsequently, after the substorm expansive phase onset at earth, the distant tail undergoes a sequence of plasma, field, and energetic-particle variations as large-scale plasmoids move rapidly down the tail following their disconnection from the near-earth plasma sheet. ISEE 3 data are appropriate for the study of these effects since the spacecraft remained fixed within the nominal tail location for long periods. Using newly available auroral electrojet indices (AE and AL) and Geo particle data to time substorm onsets at earth, superposed epoch analyses of ISEE 3 and near-earth data prior to, and following, substorm expansive phase onsets have been performed. These analyses quantify and extend substantially the understanding of the deep-tail pattern of response to global substorm-induced dynamical effects.

  5. Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter

    Directory of Open Access Journals (Sweden)

    M. Platino

    2004-07-01

    Full Text Available It is now well known that amplitude modulated HF transmissions into the ionosphere can be used to generate ELF/VLF signals using the so-called "electrojet antenna". Although most observations of the generated ELF/VLF signals have been made on the ground, several low and high-altitude satellite observations have also been reported (James et al., 1990. One of the important unknowns in the physics of ELF/VLF wave generation by ionospheric heating is the volume of the magnetosphere illuminated by the ELF/VLF waves. In an attempt to investigate this question further, ground-satellite conjunction experiments have recently been conducted using the four Cluster satellites and the HF heater of the High-Frequency Active Auroral Research Program (HAARP facility in Gakona, Alaska. Being located on largely closed field lines at L≈4.9, HAARP is currently also being used for ground-to-ground type of ELF/VLF wave-injection experiments, and will be increasingly used for this purpose as it is now being upgraded for higher power operation. In this paper, we describe the HAARP installation and present recent results of the HAARP-Cluster experiments. We give an overview of the detected ELF/VLF signals at Cluster, and a possible explanation of the spectral signature detected, as well as the determination of the location of the point of injection of the HAARP ELF/VLF signals into the magnetosphere using ray tracing.

  6. Mapping plasma structures in the high-latitude ionosphere using beacon satellite, incoherent scatter radar and ground-based magnetometer observations

    Directory of Open Access Journals (Sweden)

    T. Neubert

    2002-06-01

    Full Text Available In the autumn of the year 2000, four radio receivers capable of tracking various beacon satellites were set up along the southwestern coast of Greenland. They are used to reconstruct images of the ionospheric plasma density distribution via the tomographic method. In order to test and validate tomographic imaging under the highly variable conditions often prevailing in the high-latitude ionosphere, a time interval was selected when the Sondrestrom incoherent scatter radar conducted measurements of the ionospheric plasma density while the radio receivers tracked a number of beacon satellites. A comparison between two-dimensional images of the plasma density distribution obtained from the radar and the satellite receivers revealed generally good agreement between radar measurements and tomographic images. Observed discrepancies can be attributed to F region plasma patches moving through the field of view with a speed of several hundred meters per second, thereby smearing out the tomographic image. A notable mismatch occurred around local magnetic midnight when a magnetospheric substorm breakup occurred in the vicinity of southwest Greenland (identified from ground-based magnetometer observations. The breakup was associated with a sudden intensification of the westward auroral electrojet which was centered at about 69 and extended up to some 73 corrected geomagnetic latitude. Ground-based magnetometer data may thus have the potential of indicating when the tomographic method is at risk and may fail. We finally outline the application of tomographic imaging, when combined with magnetic field data, to estimate ionospheric Joule heating rates.

  7. Ambiguities in Determination Of Self-Affinity in the AE-index Time Series

    CERN Document Server

    Watkins, N W; Rhodes, C S; Rowlands, G

    2001-01-01

    The interaction between the Earth's magnetic field and the solar wind plasma results in a natural plasma confinement system which stores energy. Dissipation of this energy through Joule heating in the ionosphere can be studied via the Auroral Electrojet (AE) index. The apparent broken power law form of the frequency spectrum of this index has motivated investigation of whether it can be described as fractal coloured noise. One frequently-applied test for self-affinity is to demonstrate linear scaling of the logarithm of the structure function of a time series with the logarithm of the dilation factor $\\lambda$. We point out that, while this is conclusive when applied to signals that are self-affine over many decades in $\\lambda$, such as Brownian motion, the slope deviates from exact linearity and the conclusions become ambiguous when the test is used over shorter ranges of $\\lambda$. We demonstrate that non self-affine time series made up of random pulses can show near-linear scaling over a finite dynamic ra...

  8. The Level of Turbulence in the Solar Wind and the Driving of the Earth's Magnetosphere

    Science.gov (United States)

    Borovsky, J. E.; Gosling, J. T.

    2001-05-01

    Times when the level of magnetic-field fluctuations in the solar wind are very small (IMF calm) are compared with "normal" times (IMF noisy). Using ISEE-3 and ISEE-2 data, for a given value of solar-wind vBz, it is found that the auroral electrojet indices AE, AU, and AL and the planetary index KP are substantial reduced in magnitude when the IMF is calm. This is particularly true for times when the IMF Bz is northward. An analogy is explored between the solar-wind-driven magnetosphere and laboratory fluid-flow experiments in which the drag on an obstacle in the flow and the structure of the fluid wake behind the obstacle are varied by injecting turbulence of various amplitudes in the upstream fluid. The laboratory results are explained with the concept that turbulent eddy viscosity, which is a function of the turbulence amplitude, controls the coupling of the fluid to the obstacle. This eddy-viscosity-coupling concept is explored for the solar-wind driving the magnetosphere via the magnetosheath. A clue as to why SMCs (steady magnetospheric convection events) occur may be uncovered.

  9. The characteristics of solar wind magnetic field during the negative-AU and large-AU (>1200nT) events

    Science.gov (United States)

    Lyu, L. H.; Kao, W.

    2014-12-01

    The negative-AU events are relatively unusual, which have caught our attention. To understand the cause of negative AU, we first eliminate the ring-current effect by considering only the events with AUFriis-Christensen et al. (1972) and Sumaruk & Feldstein (1973). Enhancement of electric jet in opposite direction is expected to be found when the IMF-By is positive. To verify their models we also examine the strong AU events with AU > 1200nT. We found that these large-AU events are associated with IMF-Bz0. Both negative-AU and large-AU events tend to occur during the beginning of the main phase of a strong magnetic storm with Kp= 7~9. The enhancement of Cowling electrojet has been proposed by Kan et al. (2011) for the triggering of substorm onset. We will discuss the possibility that a similar enhancement process might take place in the dayside auroral oval during these extreme AU events.

  10. ELF/VLF wave generation from the beating of two HF ionospheric heating sources

    Science.gov (United States)

    Cohen, M. B.; Moore, R. C.; Golkowski, M.; Lehtinen, N. G.

    2012-12-01

    It is well established that Extremely Low Frequency (ELF, 0.3-3 kHz) and Very Low Frequency (VLF, 3-30 kHz) radio waves can be generated via modulated High Frequency (HF, 3-10 MHz) heating of the lower ionosphere (60-100 km). The ionospheric absorption of HF power modifies the conductivity of the lower ionosphere, which in the presence of natural currents such as the auroral electrojet, creates an `antenna in the sky.' We utilize a theoretical model of the HF to ELF/VLF conversion and the ELF/VLF propagation, and calculate the amplitudes of the generated ELF/VLF waves when two HF heating waves, separated by the ELF/VLF frequency, are transmitted from two adjacent locations. The resulting ELF/VLF radiation pattern exhibits a strong directional dependence (as much as 15 dB) that depends on the physical spacing of the two HF sources. This beat wave source can produce signals 10-20 dB stronger than those generated using amplitude modulation, particularly for frequencies greater than 5-10 kHz. We evaluate recent suggestions that beating two HF waves generates ELF/VLF waves in the F-region (>150 km), and conclude that those experimental results may have misinterpreted, and can be explained strictly by the much more well established D region mechanism.

  11. Reply to comment by Kil et al. on "The night when the auroral and equatorial ionospheres converged"

    Science.gov (United States)

    Martinis, Carlos; Baumgardner, Jeffrey; Mendillo, Michael; Wroten, Joei; Coster, Anthea J.; Paxton, Larry J.

    2016-10-01

    One of the goals of the Martinis et al. (2015) (M15) paper was to stimulate interest in the topic of "severe events during moderate geomagnetic storms"—and we succeeded. We welcome the Comment by Kil et al. (2016) (K16) who identified weak signatures related to medium-scale traveling ionospheric disturbances (MSTIDs) and tried to argue that airglow depletion signatures of equatorial spread F (ESF) were not present. We agree with K16 in that MSTIDs were present to the north of the all-sky imager, but only during the early observations. They are easily distinguished from the ESF-related dark structures observed at the same time to the south of the imager. We stress some observational facts that K16 overlooked or erroneously used to support their case. M15 offered evidence and discussion evidence and discussion of a dynamical pattern—both in space and time domains—and the counter arguments by K16 should have dealt with the same places and same times. We also point out that the GPS data shown by K16 do not provide any information below 30° geographic latitude in the longitude sector covered by the all-sky imager. This is the region where the ESF structures appeared first and grew to reach higher latitudes. We believe that the issues addressed by K16 do not provide conclusive evidence to rule out the interpretation given by M15 on the nature of the airglow depletions observed at McDonald Observatory.

  12. Electron cyclotron waves in the presence of parallel electric fields in the Earthś auroral plasma

    Science.gov (United States)

    Kumar, S.; Dixit, S. K.; Gwal, A. K.

    1997-01-01

    The electron cyclotron waves that originate at low altitudes (regions. Acknowledgements. The authors are grateful to Prof. D. J. Southwood (Imperial College, London), J. C. Samson (University of Alberta, Edmonton), L. J. Lanzerotti (AT&T Bell Laboratories), A. Wolfe (New York City Technical College) and to Dr. M. Vellante (University of LÁquila) for helpful discussions. They also thank Dr. A. Meloni (Istituto Nazionale di Geofisica, Roma) who made available geomagnetic field observations from LÁquila Geomagnetic Observatory. This research activity at LÁquila is supported by MURST (40% and 60% contracts) and by GIFCO/CNR. Topical Editor K.-H. Glaßmeier thanks C. Waters and S. Fujita for their help in evaluating this paper.-> Correspondence to :P. Francia->

  13. Electromagnetic interference impact of the proposed emitters for the High Frequency Active Auroral Research Program (HAARP). Interim report

    Energy Technology Data Exchange (ETDEWEB)

    Robertshaw, G.A.; Snyder, A.L.; Weiner, M.M.

    1993-05-14

    The proposed HAARP emitters at the Gakona (Alaska) preferred site and at the Clear AFS (Alaska) alternative site are the Ionospheric Research Instrument (IRI), the Incoherent Scatter Radar (ISR), and the Vertical Incidence Sounder(VIS). The electromagnetic interference (EMI) impact of those emitters on receiving systems in the vicinity of the sites is estimated in this study. The results are intended for use as an input to the Air Force Environmental Impact Statement as part of the Environmental Impact Analysis Process.

  14. High Frequency Active Auroral Research Program (HAARP) imager. Final report, 29 August 1991-29 August 1993

    Energy Technology Data Exchange (ETDEWEB)

    Lance, C.; Eather, R.

    1993-09-30

    A low-light-level monochromatic imaging system was designed and fabricated which was optimized to detect and record optical emissions associated with high-power rf heating of the ionosphere. The instrument is capable of detecting very low intensities, of the order of 1 Rayleigh, from typical ionospheric atomic and molecular emissions. This is achieved through co-adding of ON images during heater pulses and subtraction of OFF (background) images between pulses. Images can be displayed and analyzed in real time and stored in optical disc for later analysis. Full image processing software is provided which was customized for this application and uses menu or mouse user interaction.

  15. Environmental Impact Analysis Process. Final Environmental Impact Statement. Part 2. Proposed High Frequency Active Auroral Research Program.

    Science.gov (United States)

    1993-07-01

    Mountain. 152 MHz 153 MHz 158 MHz SU4.14-69 Pump Station 11 p. 12-84 451 MHz 456 MHz ArirGround VHF Gulkana Airport 122 MHz Intrusion Microwave Gulkana...raised S0 degrees Farenheit in the 4.15-8 ionisphere. The EIS states that the temperature will be raised in lower elevations but does not indicate by

  16. Simulations and observations of plasma depletion, ion composition, and airglow emissions in two auroral ionospheric depletion experiments

    Science.gov (United States)

    Yau, A. W.; Whalen, B. A.; Harris, F. R.; Gattinger, R. L.; Pongratz, M. B.

    1985-01-01

    Observations of plasma depletion, ion composition modification, and airglow emissions in the Waterhole experiments are presented. The detailed ion chemistry and airglow emission processes related to the ionospheric hole formation in the experiment are examined, and observations are compared with computer simulation results. The latter indicate that the overall depletion rates in different parts of the depletion region are governed by different parameters.

  17. Efficient particle-in-cell simulation of auroral plasma phenomena using a CUDA enabled graphics processing unit

    Science.gov (United States)

    Sewell, Stephen

    This thesis introduces a software framework that effectively utilizes low-cost commercially available Graphic Processing Units (GPUs) to simulate complex scientific plasma phenomena that are modeled using the Particle-In-Cell (PIC) paradigm. The software framework that was developed conforms to the Compute Unified Device Architecture (CUDA), a standard for general purpose graphic processing that was introduced by NVIDIA Corporation. This framework has been verified for correctness and applied to advance the state of understanding of the electromagnetic aspects of the development of the Aurora Borealis and Aurora Australis. For each phase of the PIC methodology, this research has identified one or more methods to exploit the problem's natural parallelism and effectively map it for execution on the graphic processing unit and its host processor. The sources of overhead that can reduce the effectiveness of parallelization for each of these methods have also been identified. One of the novel aspects of this research was the utilization of particle sorting during the grid interpolation phase. The final representation resulted in simulations that executed about 38 times faster than simulations that were run on a single-core general-purpose processing system. The scalability of this framework to larger problem sizes and future generation systems has also been investigated.

  18. Magnetosphere-ionosphere coupling at Jupiter-like exoplanets with internal plasma sources: implications for detectability of auroral radio emissions

    CERN Document Server

    Nichols, J D

    2011-01-01

    In this paper we provide the first consideration of magnetosphere-ionosphere coupling at Jupiter-like exoplanets with internal plasma sources such as volcanic moons. We estimate the radio power emitted by such systems under the condition of near-rigid corotation throughout the closed magnetosphere, in order to examine the behaviour of the best candidates for detection with next generation radio telescopes. We thus estimate for different stellar X-ray-UV (XUV) luminosity cases the orbital distances within which the ionospheric Pedersen conductance would be high enough to maintain near-rigid corotation, and we then consider the magnitudes of the large-scale magnetosphere-ionosphere currents flowing within the systems, and the resulting radio powers, at such distances. We also examine the effects of two key system parameters, i.e. the planetary angular velocity and the plasma mass outflow rate from sources internal to the magnetosphere. In all XUV luminosity cases studied, a significant number of parameter combi...

  19. Investigating storm-enhanced density and polar tongue of ionization development during the 22 October 1999 great storm

    Science.gov (United States)

    Horvath, Ildiko; Lovell, Brian C.

    2015-02-01

    We investigate large-scale plasma density increases occurring during the 22 October 1999 great storm and focus on storm-enhanced density (SED) and polar tongue of ionization (TOI) development. Observations include two-hourly Global Ionosphere Map series coupled with multi-instrument in situ, space-based, and ground-based data plots, with Super Dual Auroral Radar Network two-cell convection maps and with model-generated neutral wind vector maps. Results demonstrate the equatorial electrojet events occurring in the Australian and American sectors, the high-density plasma features, and their underlying plasma transportation processes. During the main phase, a series of four prompt penetration electric field (PPEF) events occurred with subauroral polarization stream E field development forming a plasmaspheric drainage plume. These E field events caused the repeated development of equatorial ionization anomaly (EIA), SED bulge, and SED plume during the local dusk-midnight hours in those sectors that covered these local times. Showing a westward movement in accordance with their local time dependence, the EIA-SED structure developed first in the American sector, later on over the Pacific, and finally in the Australian sector. The SED plume plasma found its way into the polar cap through the dayside cusp region, created in the north some large polar cap enhancements reaching up to seven times of the quiet time levels, and evolved in each hemisphere into a polar TOI. We speculate that the enhanced growth of EIA, transporting high-density solar-produced plasma to the SED bulge via strong net eastward E field effects, and the mechanical effects of equatorward neutral winds contributed to the polar TOI's increasingly better development.

  20. Latitudinal profile of the ionospheric disturbance dynamo magnetic signature: comparison with the DP2 magnetic disturbance

    Directory of Open Access Journals (Sweden)

    K. Z. Zaka

    2009-09-01

    Full Text Available During magnetic storms, the auroral electrojets intensification affects the thermospheric circulation on a global scale. This process which leads to electric field and current disturbance at middle and low latitudes, on the quiet day after the end of a storm, has been attributed to the ionospheric disturbance dynamo (Ddyn. The magnetic field disturbance observed as a result of this process is the reduction of the H component amplitude in the equatorial region which constitutes the main characteristic of the ionospheric disturbance dynamo process, associated with a westward electric current flow. The latitudinal profile of the Ddyn disturbance dynamo magnetic signature exhibits an eastward current at mid latitudes and a westward one at low latitudes with a substantial amplification at the magnetic equator. Such current flow reveals an "anti-Sq" system established between the mid latitudes and the equatorial region and opposes the normal Sq current vortex. However, the localization of the eastward current and consequently the position and the extent of the "anti-Sq" current vortex changes from one storm to another. Indeed, for a strong magnetic storm, the eastward current is well established at mid latitudes about 45° N and for a weak magnetic storm, the eastward current is established toward the high latitudes (about 60° N, near the Joule heating region, resulting in a large "anti-Sq" current cell. The latitudinal profile of the Ddyn disturbance as well as the magnetic disturbance DP2 generated by the mechanism of prompt penetration of the magnetospheric convection electric field in general, show a weak disturbance at the low latitudes with a substantial amplification at the magnetic equator. Due to the intensity of the storm, the magnitude of the DP2 appears higher than the Ddyn over the American and Asian sector contrary to the African sector.

  1. Solar wind-magnetosphere coupling efficiency during ejecta and sheath-driven geomagnetic storms

    Science.gov (United States)

    Myllys, M.; Kilpua, E. K. J.; Lavraud, B.; Pulkkinen, T. I.

    2016-05-01

    We have investigated the effect of key solar wind driving parameters on solar wind-magnetosphere coupling efficiency during sheath and magnetic cloud-driven storms. The particular focus of the study was on the coupling efficiency dependence with Alfvén Mach number (MA). The efficiency has been estimated using the dawn-dusk component of the interplanetary electric field (EY), Newell and Borovsky functions as a proxy for the energy inflow and the polar cap potential (PCN), and auroral electrojet (AE) and SYM-H indices as the measure of the energy output. We have also performed a time delay analysis between the input parameters and the geomagnetic indices. The optimal time lag and smoothing window length depend on the coupling function used and on the solar wind driver. For example, turbulent sheaths are more sensitive to the time shift and the averaging interval than smoother magnetic clouds. The results presented in this study show that the solar wind-magnetosphere coupling efficiency depends strongly on the definition used, and it increases with increasing MA. We demonstrate that the PCN index distinctively shows both a Mach number dependent saturation and a Mach number independent saturation, pointing to the existence of at least two underlying physical mechanisms for the saturation of the index. By contrast, we show that the AE index saturates but that the saturation of this index is independent of the solar wind Mach number. Finally, we find that the SYM-H index does not seem to saturate and that the absence of saturation is independent of the Mach number regime. We highlight the difference between the typical MA conditions during sheath regions and magnetic clouds. The lowest MA values are related to the magnetic clouds. As a consequence, sheaths typically have higher solar wind-magnetosphere coupling efficiencies than magnetic clouds.

  2. Extreme geomagnetically induced currents

    Science.gov (United States)

    Kataoka, Ryuho; Ngwira, Chigomezyo

    2016-12-01

    We propose an emergency alert framework for geomagnetically induced currents (GICs), based on the empirically extreme values and theoretical upper limits of the solar wind parameters and of d B/d t, the time derivative of magnetic field variations at ground. We expect this framework to be useful for preparing against extreme events. Our analysis is based on a review of various papers, including those presented during Extreme Space Weather Workshops held in Japan in 2011, 2012, 2013, and 2014. Large-amplitude d B/d t values are the major cause of hazards associated with three different types of GICs: (1) slow d B/d t with ring current evolution (RC-type), (2) fast d B/d t associated with auroral electrojet activity (AE-type), and (3) transient d B/d t of sudden commencements (SC-type). We set "caution," "warning," and "emergency" alert levels during the main phase of superstorms with the peak Dst index of less than -300 nT (once per 10 years), -600 nT (once per 60 years), or -900 nT (once per 100 years), respectively. The extreme d B/d t values of the AE-type GICs are 2000, 4000, and 6000 nT/min at caution, warning, and emergency levels, respectively. For the SC-type GICs, a "transient alert" is also proposed for d B/d t values of 40 nT/s at low latitudes and 110 nT/s at high latitudes, especially when the solar energetic particle flux is unusually high.

  3. On the Usage of Geomagnetic Indices for Data Selection in Internal Field Modelling

    Science.gov (United States)

    Kauristie, K.; Morschhauser, A.; Olsen, N.; Finlay, C. C.; McPherron, R. L.; Gjerloev, J. W.; Opgenoorth, H. J.

    2016-12-01

    We present a review on geomagnetic indices describing global geomagnetic storm activity (Kp, am, Dst and dDst/dt) and on indices designed to characterize high latitude currents and substorms (PC and AE-indices and their variants). The focus in our discussion is in main field modelling, where indices are primarily used in data selection criteria for weak magnetic activity. The publicly available extensive data bases of index values are used to derive joint conditional Probability Distribution Functions (PDFs) for different pairs of indices in order to investigate their mutual consistency in describing quiet conditions. This exercise reveals that Dst and its time derivative yield a similar picture as Kp on quiet conditions as determined with the conditions typically used in internal field modelling. Magnetic quiescence at high latitudes is typically searched with the help of Merging Electric Field (MEF) as derived from solar wind observations. We use in our PDF analysis the PC-index as a proxy for MEF and estimate the magnetic activity level at auroral latitudes with the AL-index. With these boundary conditions we conclude that the quiet time conditions that are typically used in main field modelling ( PC-300 nT) can take place, when these criteria prevail. Although AE-indices have been designed to probe electrojet activity only in average conditions and thus their performance is not optimal during weak activity, we note that careful data selection with advanced AE-variants may appear to be the most practical way to lower the elevated RMS-values which still exist in the residuals between modeled and observed values at high latitudes. Recent initiatives to upgrade the AE-indices, either with a better coverage of observing stations and improved baseline corrections (the SuperMAG concept) or with higher accuracy in pinpointing substorm activity (the Midlatitude Positive Bay-index) will most likely be helpful in these efforts.

  4. Modelling of ionospheric irregularities during geomagnetic storms over African low latitude region

    Science.gov (United States)

    Mungufeni, Patrick

    2016-07-01

    In this study, empirical models of occurrence of ionospheric irregularities over low latitude African region during geomagnetic storms have been developed. The geomagnetic storms considered consisted of Dst ≤ -50 nT. GNSS-derived ionospheric Total Electron Content (TEC) data over Libreville, Gabon (NKLG) (0.35° N, 9.68° E, geographic, 8.05° S, magnetic) and Malindi, Kenya (MAL2) (2.99° S, 40.19° E, geographic, 12.42° S, magnetic) during 2000 - 2014 were used. Ionospheric irregularities at scale- lengths of a few kilometers and ˜400 m were represented with the rate of change of TEC index (ROTI). The inputs for the models are the local time, solar flux index, Auroral Electrojet index, day of the year, and the Dst index, while the output is the median ROTI during these given conditions. To develop the models, the ROTI index values were binned based on the input parameters and cubic B splines were then fitted to the binned data. Developed models using data over NKLG and MAL2 were validated with independent data over stations within 510 km and 680 km radius, respectively. The models captured the enhancements and inhibitions of the occurrence of the ionospheric irregularities during the storm period. The models even emulated these patterns in the various seasons, during medium and high solar activity conditions. The correlation coefficients for the validations were statistically significant and ranged from 0.58 - 0.73, while the percentage of the variance in the observed data explained by the modelled data ranged from 34 - 53.

  5. THEMIS observations of double-onset substorms and their association with IMF variations

    Directory of Open Access Journals (Sweden)

    C.-C. Cheng

    2011-03-01

    Full Text Available On 16 July 2008, two pairs of consecutive bursts of Pi2 pulsations were recorded simultaneously across the THEMIS ground-based observatory system. Wavelet transformation reveals that for each high-latitude pair, the dominant frequency of the first burst is higher than that of the second. But at low latitudes, the dominant frequency does not change. It is suggested that both pairs result from fast magnetospheric cavity waves with the second burst also containing shear Alfvén waves. INTERMAGNET magnetograms at auroral latitudes showed magnetic variations affected by two recurrent electrojets for each pair. The ground-based magnetometers and those at geostationary orbit sensed magnetic perturbations consistent with the formation of the substorm current wedge. Four consecutive enhancements of energetic electron and ion fluxes detected by the THEMIS probes in the dayside magnetosphere appeared in the later afternoon and then in the early afternoon. The horizontal magnetic variation vectors had vortex patterns similar to those induced by the upward and downward field-aligned currents during substorm times. The hodogram at mid-L stations had a polarization pattern similar to the one induced by the substorm current wedge for each Pi2 burst. The mapping of ground Pi2 onset timing to the interplanetary magnetic field (IMF observations shows that they appear under two cycles of north-to-south and then north variation. CLUSTER 4 in the south lobe observed wave-like magnetic fluctuations, probably driven by near-Earth reconnection, similar to those on the ground. These two observations are consistent with the link of double-onset substorms to magnetotail reconnection externally triggered by IMF variations.

  6. Studies of the auroral-zone ionosphere using the MITHRAS data base. Fiscal years 1983-1985. Final report, October 1982-October 1985

    Energy Technology Data Exchange (ETDEWEB)

    1986-06-26

    The Autmospheric Science group participated in the multi-radar MITHRAS experimental campaign. Coordinated observations of the earth's ionosphere, magnetosphere, and thermosphere were conducted using the Millstone Hill, Massachusetts, Chatanika, Alaska, and European EISCAT incoherent scatter radars in conjunction with a variety of ground-based and satellite experiments. Chatanika and EISCAT are about 11 hours apart in magnetic local time, and Millstone Hill precedes Chatanika and follows EISCAT by more than 6 hours. Each of the three radars was able to study aruroal-zone latitudes, but at widely spaced longitudes. Hence the MITHRAS program was well suited to study the class of problems which involve universal time/local time ambiguities, or equivalenty, space/time differences. Set operating modes were used at the radar sites to best match the requirements of the several campaign objectives. The overall MITHRAS program was motivated by a desire to provide a well documented set of radar observations of the mid- and high-latitude ionosphere during the brief interval when three incoherent scatter facialities would be available. At Millstone Hill the MITHRAS program involved the development of specific radar operating modes and analysis techniques appropriate for multi-instrument studies. An extensive data set resulted from the campaign.

  7. Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 July-30 September 1995

    Energy Technology Data Exchange (ETDEWEB)

    Aarons, J.; Mendillo, M.

    1995-09-30

    Radar data from Jicamarca, Peru and phase fluctuation data from Arequipa, Santiago, and Kourou were used to study the occurrence and intensity of phase fluctuations of GPS signals. In the study of 14 days of campaign equatorial data, there was a longitudinal separation of 5.5 degrees between the overhead field line at the radar site at Jicamarca and the overhead field line at Arequipa. The authors have started a study to relate GPS phase fluctuations at the equator with the Bz component of a high latitude magnetogram. For this initial study, there was a lack of correlation between magnetic activity and phase fluctuation but more complex studies involving a larger data base and more attention to ambient conditions will be instituted in the future.

  8. Magnetospheric mapping of the dayside UV auroral oval at Saturn using simultaneous HST images, Cassini IMF data, and a global magnetic field model

    Directory of Open Access Journals (Sweden)

    E. S. Belenkaya

    2011-07-01

    Full Text Available We determine the field-aligned mapping of Saturn's auroras into the magnetosphere by combining UV images of the southern dayside oval obtained by the Hubble Space Telescope (HST with a global model of the magnetospheric magnetic field. The model is tailored to simulate prevailing conditions in the interplanetary medium, corresponding to high solar wind dynamic pressure and variable interplanetary magnetic field (IMF strength and direction determined from suitably lagged field data observed just upstream of Saturn's dayside bow shock by the Cassini spacecraft. Two out of four images obtained in February 2008 when such simultaneous data are available are examined in detail, exemplifying conditions for northward and southward IMF. The model field structure in the outer magnetosphere and tail is found to be very different in these cases. Nevertheless, the dayside UV oval is found to have a consistent location relative to the field structure in each case. The poleward boundary of the oval is located close to the open-closed field boundary and thus maps to the vicinity of the magnetopause, consistent with previous results. The equatorward boundary of the oval then maps typically near the outer boundary of the equatorial ring current appropriate to the compressed conditions prevailing. Similar results are also found for related images from the January 2004 HST data set. These new results thus show that the mapped dayside UV oval typically spans the outer magnetosphere between the outer part of the ring current and the magnetopause. It does not encompass the region of primary corotation flow breakdown within the inner Enceladus torus.

  9. Satellite and Ground-Based Observations of Auroral Energy Deposition and the Effects on Thermospheric Composition During Large Geomagnetic Storms: 1. Great Geomagnetic Storm of 20 November 2003

    Science.gov (United States)

    2008-01-01

    studies during both distribution of low-energy electrons well below 1 keV that are geomagnetically quiet and disturbed periods [e.g., see Nier the suspected...4510. energies inferred from the Sondre Stromtjord radar, J. Geophys. Res., 96, Nier , A. 0., W. E. Potter, and D. C. Kayser (1976), Atomic and

  10. High latitude electromagnetic plasma wave emissions

    Science.gov (United States)

    Gurnett, D. A.

    1983-01-01

    The principal types of electromagnetic plasma wave emission produced in the high latitude auroral regions are reviewed. Three types of radiation are described: auroral kilometric radiation, auroral hiss, and Z mode radiation. Auroral kilometric radiation is a very intense radio emission generated in the free space R-X mode by electrons associated with the formation of discrete auroral arcs in the local evening. Theories suggest that this radiation is an electron cyclotron resonance instability driven by an enhanced loss cone in the auroral acceleration region at altitudes of about 1 to 2 R sub E. Auroral hiss is a somewhat weaker whistler mode emission generated by low energy (100 eV to 10 keV) auroral electrons. The auroral hiss usually has a V shaped frequency time spectrum caused by a freqency dependent beaming of the whistler mode into a conical beam directed upward or downward along the magnetic field.

  11. Nightside studies of coherent HF Radar spectral width behaviour

    Directory of Open Access Journals (Sweden)

    E. E. Woodfield

    Full Text Available A previous case study found a relationship between high spectral width measured by the CUTLASS Finland HF radar and elevated electron temperatures observed by the EISCAT and ESR incoherent scatter radars in the post-midnight sector of magnetic local time. This paper expands that work by briefly re-examining that interval and looking in depth at two further case studies. In all three cases a region of high HF spectral width (>200 ms-1 exists poleward of a region of low HF spectral width (<200 ms-1. Each case, however, occurs under quite different geomagnetic conditions. The original case study occurred during an interval with no observed electrojet activity, the second study during a transition from quiet to active conditions with a clear band of ion frictional heating indicating the location of the flow reversal boundary, and the third during an isolated sub-storm. These case studies indicate that the relationship between elevated electron temperature and high HF radar spectral width appears on closed field lines after 03:00 magnetic local time (MLT on the nightside. It is not clear whether the same relationship would hold on open field lines, since our analysis of this relationship is restricted in latitude. We find two important properties of high spectral width data on the nightside. Firstly the high spectral width values occur on both open and closed field lines, and secondly that the power spectra which exhibit high widths are both single-peak and multiple-peak. In general the regions of high spectral width (>200 ms-1 have more multiple-peak spectra than the regions of low spectral widths whilst still maintaining a majority of single-peak spectra. We also find that the region of ion frictional heating is collocated with many multiple-peak HF spectra. Several mechanisms for the generation of high spectral width have been proposed which would produce multiple-peak spectra, these are discussed in relation to

  12. EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

    Directory of Open Access Journals (Sweden)

    A. T. Aikio

    2008-02-01

    Full Text Available The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6° cgmLat and Longyearbyen (75.2° cgmLat on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB made zig-zag-type motion with amplitude of 2.5° cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL. The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992. The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm.

    During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 RE mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H+ and O+ ions took place within the plasma sheet boundary layer (PSBL as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency fluctuations.

    The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2° during

  13. A Single Linear Prediction Filter that Accurately Predicts the AL Index

    Science.gov (United States)

    McPherron, R. L.; Chu, X.

    2015-12-01

    The AL index is a measure of the strength of the westward electrojet flowing along the auroral oval. It has two components: one from the global DP-2 current system and a second from the DP-1 current that is more localized near midnight. It is generally believed that the index a very poor measure of these currents because of its dependence on the distance of stations from the source of the two currents. In fact over season and solar cycle the coupling strength defined as the steady state ratio of the output AL to the input coupling function varies by a factor of four. There are four factors that lead to this variation. First is the equinoctial effect that modulates coupling strength with peaks (strongest coupling) at the equinoxes. Second is the saturation of the polar cap potential which decreases coupling strength as the strength of the driver increases. Since saturation occurs more frequently at solar maximum we obtain the result that maximum coupling strength occurs at equinox at solar minimum. A third factor is ionospheric conductivity with stronger coupling at summer solstice as compared to winter. The fourth factor is the definition of a solar wind coupling function appropriate to a given index. We have developed an optimum coupling function depending on solar wind speed, density, transverse magnetic field, and IMF clock angle which is better than previous functions. Using this we have determined the seasonal variation of coupling strength and developed an inverse function that modulates the optimum coupling function so that all seasonal variation is removed. In a similar manner we have determined the dependence of coupling strength on solar wind driver strength. The inverse of this function is used to scale a linear prediction filter thus eliminating the dependence on driver strength. Our result is a single linear filter that is adjusted in a nonlinear manner by driver strength and an optimum coupling function that is seasonal modulated. Together this

  14. Resistive Heating in Saturn's Thermosphere

    Science.gov (United States)

    Vriesema, Jess W.; Koskinen, Tommi; Yelle, Roger V.

    2016-10-01

    The thermospheres of the jovian planets are several times hotter than solar heating alone can account for. On Saturn, resistive heating appears sufficient to explain these temperatures in auroral regions, but the particular mechanism(s) responsible for heating the lower latitudes remains unclear. Smith et al. (2005) suggested that electrodynamics of the equatorial region—particularly resistive heating caused by strong electrojet currents—might explain the observed temperatures at low latitudes. Müller-Wodarg et al. (2006) found that their circulation model could reproduce low-latitude temperatures only when they included resistive heating at the poles and applied a uniform, generic heating source globally. Smith et al. (2007) concluded that heating at the poles leads to meridional circulation that cools low latitudes and argued that in-situ heating is required to explain the temperatures at low latitudes.Resistive heating at low latitudes, arising from enhanced current generation driven by thermospheric winds, is a potentially important in-situ heating mechanism. Ion drag caused by low-latitude electrodynamics can modify global circulation and meridional transport of energy. We present an axisymmetric, steady-state formulation of wind-driven electrodynamics to investigate these possibilities throughout Saturn's thermosphere. At present, we assume a dipole magnetic field and neglect any contributions from the magnetosphere. We use ion mixing ratios from the model of Kim et al. (2014) and the observed temperature-pressure profile from Koskinen et al. (2015) to calculate the generalized conductivity tensor as described by Koskinen et al. (2014). Our model solves the coupled equations for charge continuity and Ohm's law with tensor conductivity while enforcing zero current across the boundaries. The resulting partial differential equation is solved for the current density throughout the domain and used to calculate the net resistive heating rate. We demonstrate

  15. U.S. national report to the International Union of Geodesy and Geophysics

    Science.gov (United States)

    Gorney, D. J.

    1987-01-01

    This paper highlights progress by U.S. authors during 1983-1986 in the broad area of auroral research. Atmospheric emissions and their use as a tool for remote-sensing the dynamics, energetics, and effects of auroral activity is a subject which is emphasized here because of the vast progress made in this area on both observational and theoretical fronts. The evolution of primary auroral electrons, the acceleration of auroral ions, small-scale electric fields, auroral kilometric radiation, auroral empirical models and activity indices are also reviewed. An extensive bibliography is supplied.

  16. Colloid Thrusters, Physics, Fabrication and Performance

    Science.gov (United States)

    2005-11-17

    response, including the time for reviewing in. tata needed, and completing and reviewing this collection of information. Send comments regarding this...a discussion with colleagues during the 2nd Colloid Thruster/ Nano Electrojet Workshop (MIT, April 14- 15, 2005, Ref. [11]) an agreement was reached...23 Jul 2003. 11. Second Colloid Thruster/ Nano Electrojet Workshop, CD with a collection of presentations by attendees to this Workshop. MIT, April 14

  17. Compression and Processing of Space Image Sequences of Northern Lights and Sprites

    DEFF Research Database (Denmark)

    Forchhammer, Søren Otto; Martins, Bo; Jensen, Ole Riis

    1999-01-01

    Compression of image sequences of auroral activity as northern lights and thunderstorms with sprites is investigated.......Compression of image sequences of auroral activity as northern lights and thunderstorms with sprites is investigated....

  18. The International Symposium on Equatorial Aeronomy (10th) Held in Antalya, Turkey on May 17-23, 2000

    Science.gov (United States)

    2006-05-31

    Marriot et al. (1979), Reddy (1989), Somayajulu et al. (1993), Stening et al. (1996) and the references therein], the causative mechanism for its...1993)]. Marriot (1979) using Richmond’s (1973) steady-state and ’infinite counductivity model’ of the electrojet, found that the diurnal tide is the

  19. Microencapsulation of chemotherapeutics into monodisperse and tunable biodegradable polymers via electrified liquid jets: control of size, shape, and drug release.

    Science.gov (United States)

    Fattahi, Pouria; Borhan, Ali; Abidian, Mohammad Reza

    2013-09-06

    This paper describes microencapsulation of antitumor agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU, Carmustine) into biodegradable polymer poly(lactic-co-glycolic) acid (PLGA) using an electrojetting technique. The resulting BCNU-loaded PLGA microcapsules have significantly higher drug encapsulation efficiency, more tunable drug loading capacity, and (3) narrower size distribution than those generated using other encapsulation methods.

  20. Equatorial electrodynamics and neutral background in the Asian sector during the 2009 stratospheric sudden warming

    NARCIS (Netherlands)

    Liu, H.; Yamamoto, M.; Tulasi Ram, S.; Tsugawa, T.; Otsuka, Y.; Stolle, C.; Doornbos, E.; Yumoto, K.; Nagatsuma, T.

    2011-01-01

    Using ground observations of total electron content (TEC) and equatorial electrojet (EEJ) in the Asian sector, along with plasma and neutral densities obtained from the CHAMP satellite, we investigate the ionospheric electrodynamics and neutral background in this longitude sector during the major st

  1. Equatorial electrodynamics and neutral background in the Asian sector during the 2009 stratospheric sudden warming

    DEFF Research Database (Denmark)

    Liu, Huixin; Yamamoto, Mamoru; Ram, S. Tulasi;

    2011-01-01

    Using ground observations of total electron content (TEC) and equatorial electrojet (EEJ) in the Asian sector, along with plasma and neutral densities obtained from the CHAMP satellite, we investigate the ionospheric electrodynamics and neutral background in this longitude sector during the major...

  2. Testing the hypothesis of the Earth's magnetosphere behaving like an avalanching system

    Directory of Open Access Journals (Sweden)

    A. T. Y. Lui

    2004-01-01

    Full Text Available The global auroral dissipation power as observed by the imager on the Polar spacecraft is used as a proxy for the power dissipation of the Earth's magnetosphere to examine whether or not the magnetosphere is an avalanching system. It is found that the probability density distributions for the area and power of auroral activity sites have a power law component within a finite scale range, suggestive of a scale-free nature in this finite-size system. This property is robust, prevailing with variations in the threshold used to define auroral activity sites and in the strength of the external driver, namely, the solar wind. The statistical characteristics on the temporal evolution of auroral sites are then examined, which leads to a criterion that can be used to predict about 42min in advance the total energy dissipation during the lifetime of an auroral activity site. The scale-free characteristics of auroral activity appears to be an intrinsic feature of the magnetosphere based on a comparison of the probability density distribution in the total auroral brightness power with that of the solar wind power input parameters in the same period as the auroral observations. These results are consistent with the hypothesis of the magnetosphere behaving like an avalanching system.

  3. Plasma physics abstracts, 1 January - 31 December, 1986

    Science.gov (United States)

    Gurnett, D. A.; Dangelo, N.; Goertz, C. K.

    1987-01-01

    Topics addressed include: ion-cyclotron waves; plasma waves; solar wind lithium releases; bow shock; Pi2 wave bursts; auroral kilometric radiation; ion energization; magnetic field corrections; electric fields; magnetospheric processes; electron acceleration; inner heliosphere; nightside auroral zone; computerized simulation; plasma wave turbulence; and magnetohydrodynamic waves in plasma sheets.

  4. A study of fine structure of diffuse aurora with ALIS-FAST measurements

    Directory of Open Access Journals (Sweden)

    T. Sergienko

    2008-10-01

    Full Text Available We present results of an investigation of the fine structure of the night sector diffuse auroral zone, observed simultaneously with optical instruments (ALIS from the ground and the FAST electron spectrometer from space 16 February 1997. Both the optical and particle data show that the diffuse auroral zone consisted of two regions. The equatorward part of the diffuse aurora was occupied by a pattern of regular, parallel auroral stripes. The auroral stripes were significantly brighter than the background luminosity, had widths of approximately 5 km and moved southward with a velocity of about 100 m/s. The second region, located between the region with auroral stripes and the discrete auroral arcs to the north, was filled with weak and almost homogeneous luminosity, against which short-lived auroral rays and small patches appeared chaotically. From analysis of the electron differential fluxes corresponding to the different regions of the diffuse aurora and based on existing theories of the scattering process we conclude the following: Strong pitch angle diffusion by electron cyclotron harmonic waves (ECH of plasma sheet electrons in the energy range from a few hundred eV to 3–4 keV was responsible for the electron precipitation, that produced the background luminosity within the whole diffuse zone. The fine structure, represented by the auroral stripes, was created by precipitation of electrons above 3–4 keV as a result of pitch angle diffusion into the loss cone by whistler mode waves. A so called "internal gravity wave" (Safargaleev and Maltsev, 1986 may explain the formation of the regular spatial pattern formed by the auroral stripes in the equatorward part of the diffuse auroral zone.

  5. A study of fine structure of diffuse aurora with ALIS-FAST measurements

    Science.gov (United States)

    Sergienko, T.; Sandahl, I.; Gustavsson, B.; Andersson, L.; Brändström, U.; . Steen, Ã.

    2008-10-01

    We present results of an investigation of the fine structure of the night sector diffuse auroral zone, observed simultaneously with optical instruments (ALIS) from the ground and the FAST electron spectrometer from space 16 February 1997. Both the optical and particle data show that the diffuse auroral zone consisted of two regions. The equatorward part of the diffuse aurora was occupied by a pattern of regular, parallel auroral stripes. The auroral stripes were significantly brighter than the background luminosity, had widths of approximately 5 km and moved southward with a velocity of about 100 m/s. The second region, located between the region with auroral stripes and the discrete auroral arcs to the north, was filled with weak and almost homogeneous luminosity, against which short-lived auroral rays and small patches appeared chaotically. From analysis of the electron differential fluxes corresponding to the different regions of the diffuse aurora and based on existing theories of the scattering process we conclude the following: Strong pitch angle diffusion by electron cyclotron harmonic waves (ECH) of plasma sheet electrons in the energy range from a few hundred eV to 3 4 keV was responsible for the electron precipitation, that produced the background luminosity within the whole diffuse zone. The fine structure, represented by the auroral stripes, was created by precipitation of electrons above 3 4 keV as a result of pitch angle diffusion into the loss cone by whistler mode waves. A so called "internal gravity wave" (Safargaleev and Maltsev, 1986) may explain the formation of the regular spatial pattern formed by the auroral stripes in the equatorward part of the diffuse auroral zone.

  6. The response of ionospheric convection in the polar cap to substorm activity

    Directory of Open Access Journals (Sweden)

    M. Lester

    Full Text Available We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF. We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71°λ by the time of the expansion phase onset. A westward electrojet, centred at 65.4°λ, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1°λ at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the "distant" neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap

  7. Sporadic aurorae observed in East Asia

    Directory of Open Access Journals (Sweden)

    D. M. Willis

    2007-03-01

    Full Text Available All the accessible auroral observations recorded in Chinese and Japanese histories during the interval AD 1840–1911 are investigated in detail. Most of these auroral records have never been translated into a Western language before. The East Asian auroral reports provide information on the date and approximate location of each auroral observation, together with limited scientific information on the characteristics of the auroral luminosity such as colour, duration, extent, position in the sky and approximate time of occurrence. The full translations of the original Chinese and Japanese auroral records are presented in an appendix, which contains bibliographic details of the various historical sources. (There are no known reliable Korean observations during this interval. A second appendix discusses a few implausible "auroral" records, which have been rejected. The salient scientific properties of all exactly dated and reliable East Asian auroral observations in the interval AD 1840–1911 are summarised succinctly. By comparing the relevant scientific information on exactly dated auroral observations with the lists of great geomagnetic storms compiled by the Royal Greenwich Observatory, and also the tabulated values of the Ak (Helsinki and aa (Greenwich and Melbourne magnetic indices, it is found that 5 of the great geomagnetic storms (aa>150 or Ak>50 during either the second half of the nineteenth century or the first decade of the twentieth century are clearly identified by extensive auroral displays observed in China or Japan. Indeed, two of these great storms produced auroral displays observed in both countries on the same night. Conversely, at least 29 (69% of the 42 Chinese and Japanese auroral observations occurred at times of weak-to-moderate geomagnetic activity (aa or Ak≤50. It is shown that these latter auroral displays are very similar to the more numerous (about 50 examples of sporadic

  8. Global Remote Sensing of Precipitating Electron Energies: A Comparison of Substorms and Pressure Pulse Related Intensifications

    Science.gov (United States)

    Chua, D.; Parks, G. K.; Brittnacher, M. J.; Germany, G. A.; Spann, J. F.

    2000-01-01

    The Polar Ultraviolet Imager (UVI) observes aurora responses to incident solar wind pressure pulses and interplanetary shocks such its those associated with coronal mass ejections. Previous observations have demonstrated that the arrival of it pressure pulse at the front of the magnetosphere results in highly disturbed geomagnetic conditions and a substantial increase in both dayside and nightside aurora precipitations. Our observations show it simultaneous brightening over bread areas of the dayside and nightside auroral in response to a pressure pulse, indicating that more magnetospheric regions participate as sources for auroral precipitation than during isolate substorm. We estimate the characteristic energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated event to those during isolated substorms. We estimate the characteristic energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated events to those during isolated auroral substorms. Electron precipitation during substorms has characteristic energies greater than 10 KeV and is structured both in local time and in magnetic latitude. For auroral intensifications following the arrival of'a pressure pulse or interplanetary shock. Electron precipitation is less spatially structured and has greater flux of lower characteristic energy electrons (Echar less than 7 KeV) than during isolated substorm onsets. These observations quantify the differences between global and local auroral precipitation processes and will provide a valuable experimental check for models of sudden storm commencements and magnetospheric response to perturbations in the solar wind.

  9. Imaging Sunlit Aurora from Balloon

    Science.gov (United States)

    Lummerzheim, D.; Zhou, X.

    2012-12-01

    Since 1892 when aurora was first imaged by Martin Brendel, useful auroral images have been obtained only when the aurora is in darkness. While UV imagers onboard satellite provide global auroral dynamics, the sunlit aurora in the UV band is overwhelmed by the UV airglow that has the same wavelengths with the UV auroral emissions. The visible band imaging is feasible only when the aurora is in darkness to avoid the sunlight contamination. However, sunlit aurora (such as dayside aurora) is closely related to the solar wind - magnetosphere - ionosphere coupling. In addition, limited land area has badly restricted the capability of imaging dayside aurora from the northern hemisphere and nightside aurora from the southern hemisphere. We have confirmed that sunlit aurora can be imaged using a near-infrared (NIR) camera on board the balloon platform flying in Antarctica or Arctic. This method provides a unique capability for dayside and conjugate auroral investigations. Scientific questions that can be addressed by such observations include how does the dayside aurora respond to solar wind transient variations? Are auroras hemispherically symmetric? Are auroral forms and their variations under sunlight the same as those in darkness? etc. The new method is also cost effective comparing to space-borne imagers, and offers capabilities not obtainable from space and the ground. With the accomplishment of identifying auroral dynamics in sunlight and darkness, in the south and north simultaneously, our knowledge and understanding of auroral phenomenon and its causes will be expanded.

  10. Solar wind influence on Jupiter's aurora

    Science.gov (United States)

    Gyalay, Szilard; Vogt, Marissa F.; Withers, Paul; Bunce, Emma J.

    2016-10-01

    Jupiter's main auroral emission is driven by a system of corotation enforcement currents that arises to speed up outflowing Iogenic plasma and is not due to the magnetosphere-solar wind interaction like at Earth. The solar wind is generally expected to have only a small influence on Jupiter's magnetosphere and aurora compared to the influence of rotational stresses due to the planet's rapid rotation. However, there is considerable observational evidence that the solar wind does affect the magnetopause standoff distance, auroral radio emissions, and the position and brightness of the UV auroral emissions. Using the Michigan Solar Wind Model (mSWiM) to predict the solar wind conditions upstream of Jupiter we have identified intervals of high and low solar wind dynamic pressure in the Galileo dataset, and use this information to quantify how a magnetospheric compression affects the magnetospheric field configuration. We have developed separate spatial fits to the compressed and nominal magnetic field data, accounting for variations with radial distance and local time. These two fits can be used to update the flux equivalence mapping model of Vogt et al. (2011), which links auroral features to source regions in the middle and outer magnetosphere. The updated version accounts for changing solar wind conditions and provides a way to quantify the expected solar wind-induced variability in the ionospheric mapping of the main auroral emission, satellite footprints, and other auroral features. Our results are highly relevant to interpretation of the new auroral observations from the Juno mission.

  11. On the origin of pre-reversal enhancement of the zonal equatorial electric field

    Directory of Open Access Journals (Sweden)

    M. C. Kelley

    2009-05-01

    Full Text Available In November 2004, a large and variable interplanetary electric field (IEF was felt in the reference frame of the Earth. This electric field penetrated to the magnetic equator and, when the Jicamarca Radio Observatory (JRO was in the dusk sector, resulted in a reversal of the normal zonal component of the field. In turn, this caused a counter-electrojet (CEJ, a westward current rather than the usual eastward current. At the time of the normal pre-reversal enhancement (PRE of the eastward field, the Jicamarca incoherent scatter radar (ISR observed that the westward component became even more westward. Two of the three current explanations for the PRE depend on the neutral wind patterns. However, this unique event was such that the neutral wind-driven dynamos could not have changed. The implication is that the Haerendel-Eccles mechanism, which involves partial closure of the equatorial electrojet (EEJ after sunset, must be the dominant mechanism for the PRE.

  12. Three-dimensional structure of ionospheric currents produced by field-aligned currents

    Science.gov (United States)

    Takeda, M.

    1982-08-01

    Ionospheric currents caused by field-aligned currents are calculated three-dimensionally under quiet conditions at the equinox, using a magnetic field line coordinate system and with the assumption of infinite parallel conductivity. Input field-aligned currents are assumed to be distributed only in the daytime and the whole system is assumed to be symmetric about the equator. Calculated currents are comparable with those of the ionospheric dynamo in higher latitudes, but much weaker in lower latitudes including the equatorial electrojet region. Hence, if the model is valid these currents may have a considerable effect on the day-to-day variation of Sq currents in higher latitudes, but little effect on those in lower latitudes such as the counter-electrojet.

  13. United States Air Force Summer Research Program -- 1993. Volume 3. Phillips Laboratory

    Science.gov (United States)

    1993-12-01

    of the need to understand and influence plasmas which occur naturally (e.g., auroras and the ionosphere) or man-made (e.g., around transonic aircraft...34Simultaneous Observations of ELF Waves from an Artificially Modulated Aurora Electrojet in Space and On the Ground", J. Geophys. Res., 89, 1655, 1984. James...solving hydrogeological problems," Geoexploration, vol. 14, pp. 195-206, 1976. [45] F. Bender and H. Flathe, "Groundwater conditions in the Chaco Boreal

  14. Swarm equatorial electric field chain: First results

    OpenAIRE

    Alken, P; Maus, S.; A. Chulliat; Vigneron, P.; Sirol, O.; Hulot, G.

    2015-01-01

    International audience; The eastward equatorial electric field (EEF) in the E region ionosphere drives many important phenomena at low latitudes. We developed a method of estimating the EEF from magnetometer measurements of near-polar orbiting satellites as they cross the magnetic equator, by recovering a clean signal of the equatorial electrojet current and modeling the observed current to determine the electric field present during the satellite pass. This algorithm is now implemented as an...

  15. An intense SFE and SSC event in geomagnetic H, Y and Z fields at the Indian chain of observatories

    Directory of Open Access Journals (Sweden)

    S. Alex

    Full Text Available Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC of geomagnetic storm at 1518 h on 17 June 1991. The solar flare effects (SFE registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in ΔH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H at low latitude. ΔY registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. ΔZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.

  16. A study on three-dimensional structures of the ionospheric dynamo currents induced by the neutral winds simulated by the Kyushu-GCM

    Science.gov (United States)

    Kawano-Sasaki, Keiko; Miyahara, Saburo

    2008-08-01

    Three-dimensional structures of the ionospheric dynamo currents are examined using the neutral winds in a general circulation model of the middle atmosphere at Kyushu University. A quasi-three-dimensional ionospheric dynamo model is constructed assuming an infinite parallel conductivity in the ionosphere. This model is able to simulate both the equatorial electrojet and the global Sq current system successfully. The simulated results reveal that the equatorial electrojet is confined in quite narrow latitudes around the equator accompanied with meridional current circulations and satisfies a non-divergent structure mainly within the E region. A vertically stratified double layered structure is seen in the east-west current density near the focus latitude of the global Sq current system. It is shown that the stratified structure mainly consists of the east-west Hall current associated with the eastward wind of zonal wavenumbers 1 and 2 in the lower altitudes and the westward wind of zonal wavenumber 2 in the upper altitudes. The day-to-day variation of the neutral winds can significantly vary the induced ionospheric dynamo current system, which is recognized as changes of the focus latitude and/or the maximum value of the equatorial electrojet.

  17. Ovation Prime Real-Time

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Ovation Prime Real-Time (OPRT) product is a real-time forecast and nowcast model of auroral power and is an operational implementation of the work by Newell et...

  18. Atmospheric physics: Chorus keeps the diffuse aurora humming

    Science.gov (United States)

    Newell, Patrick T.

    2010-10-01

    The origin of the diffuse aurora, whose beauty and intensity pale beside those of the famous aurora borealis, has remained controversial. A convincing explanation for this auroral display is now at hand. See Letter p.943

  19. Dynamics Explorer guest investigator

    Science.gov (United States)

    Sojka, J. J.

    1987-01-01

    Four objectives were accomplished during this reporting period. The visible auroral image conversion algorithms were compated with algorithms developed by Dr. M. H. Rees for data at different wavelengths. In the study 630 and 557 nm images were used to deduce the auroral energy flux and characteristic energy of the precipitating auroral electrons. The data for Southward IMF, B sub y negative conditions were collected and put into global format. A total of 55 sets of auroral images were obtained, and then converted to energy flux and characteristic energy data sets. The shortcoming of representing the high latitude convection pattern as a smooth function was written up and submitted to the Journal of Geophysical Research. A series of midlatitude corotational model runs were performed to quantitatively show how the F region varied as a function of electric field, topside number flux, and a topside heat source.

  20. Issues in Quantitative Analysis of Ultraviolet Imager (UV) Data: Airglow

    Science.gov (United States)

    Germany, G. A.; Richards, P. G.; Spann, J. F.; Brittnacher, M. J.; Parks, G. K.

    1999-01-01

    The GGS Ultraviolet Imager (UVI) has proven to be especially valuable in correlative substorm, auroral morphology, and extended statistical studies of the auroral regions. Such studies are based on knowledge of the location, spatial, and temporal behavior of auroral emissions. More quantitative studies, based on absolute radiometric intensities from UVI images, require a more intimate knowledge of the instrument behavior and data processing requirements and are inherently more difficult than studies based on relative knowledge of the oval location. In this study, UVI airglow observations are analyzed and compared with model predictions to illustrate issues that arise in quantitative analysis of UVI images. These issues include instrument calibration, long term changes in sensitivity, and imager flat field response as well as proper background correction. Airglow emissions are chosen for this study because of their relatively straightforward modeling requirements and because of their implications for thermospheric compositional studies. The analysis issues discussed here, however, are identical to those faced in quantitative auroral studies.

  1. The High Latitude D Region During Electron Precipitation Events

    Science.gov (United States)

    Hargreaves, J. K.; Collis, P. N.; Korth, A.

    1984-01-01

    The fluxes of energetic electrons entering the high-latitude atmosphere during auroral radio absorption events and their effect on the electron density in the auroral D region are discussed. An attempt was made to calculate the radio absorption during precipitation events from the fluxes of energetic electrons measured at geosynchronous orbit, and then to consider the use of absorption measurements to indicate the magnetospheric particle fluxes, the production rates, and electron densities in the D region.

  2. High latitude D region during electron precipitation events

    Energy Technology Data Exchange (ETDEWEB)

    Hargreaves, J.K.; Collis, P.N.; Korth, A.

    1984-05-01

    The fluxes of energetic electrons entering the high-latitude atmosphere during auroral radio absorption events and their effect on the electron density in the auroral D region are discussed. An attempt was made to calculate the radio absorption during precipitation events from the fluxes of energetic electrons measured at geosynchronous orbit, and then to consider the use of absorption measurements to indicate the magnetospheric particle fluxes, the production rates, and electron densities in the D region.

  3. Plasma flow during the brightening of proton aurora in the cusp

    DEFF Research Database (Denmark)

    Taguchi, S.; Hosokawa, K.; Suzuki, S.

    2010-01-01

    On the basis of simultaneous observations from the Super Dual Auroral Radar Network (SuperDARN), the far ultraviolet instrument on the IMAGE spacecraft, and a magnetometer installed on the east coast of Greenland, we present the characteristics of plasma flow during a westward moving proton auror...... to the traveling bulge at the polar cap boundary, which is the footprint of a flux transfer event, and imply that the preexisting vortical flow may be intensified when it becomes inflow to the bulge....

  4. World first complex optical instrumental observations of aurora in the Arctic in 1899−1900

    Directory of Open Access Journals (Sweden)

    L. S. Yevlashin

    2005-07-01

    Full Text Available This report presents data and analysis of visual, photographic and auroral spectral data, obtained by the Russian astronomer J. Sykora from the Russian-Swedish expedition to Spitsbergen during the 1899–1900 winter season, which are historically significant for auroral studies. These data seem to be the first instrumental observations of auroral spectra in the Arctic and some of the emissions discovered have world priority. The second known photos in the world of aurora from the Arctic and undoubtedly the first ones for geomagnetic latitudes of about 75° in the Spitsbergen Archipelago were obtained. The results of the expedition are discussed from a modern point of view and compared with our knowledge of the 21st century. A description of the equipment and methods that were used by Russian astronomers is presented. Both photographic and spectral devices using registration by photographic plates were used, along with special methods of their development and enhancement. Some statistical analysis was done on the basis of the expedition reports and diaries. This analysis shows that by using Sykora's data it was possible to discover the auroral oval or instantaneous auroral distribution over the polar region. Analysis of photographic samples and sketches of the aurora demonstrate typical auroral form outlines as they are described today. Spectral plates exposed for several hours to auroral lights revealed not only the main auroral emissions, which were well-known at that time, but several other unidentified weak emissions, which were rediscovered and interpreted years later. Keywords. History of geophysics (Atmospheric sciences, instruments and techniques

  5. Localization of Aurorae with 10 m High Power Radar Technique, using a Rotating Antenna

    OpenAIRE

    Hellgren, Gösta; Meos, Johan

    2011-01-01

    The paper describes the 10 m high power recorder with a rotating antenna that is used since May 1951 for the localization of aurorae at the Radio Wave Propagation Laboratory of the Kiruna Geophysical Observatory (67.8° N, 20.5° E). Continuous observations during the time May 1951–March 1952 have disclosed periods of auroral activity. The preliminary results from these observations indicate that there is a good correlation between the auroral activity, the magnetic activity, and ...

  6. Recent Results of the Remote Sensing of the O/N2 Ratio in the 100 to 200 Km Altitude Region

    Science.gov (United States)

    Hecht, J. H.

    2014-12-01

    The O/N2 ratio is a sensitive indicator of dynamical changes in the composition of the lower Thermosphere. In the auroral zone the deposition of auroral energy (either through particle precipitation or Joule heating) can produce changes in vertical winds causing a decrease in the O/N2 ratio. Horizontal winds may transport O-depleted air away from the auroral zone causing composition changes in the latitude regions equatorward of the auroral zone. Large waves and tides may also affect composition. To measure such composition changes a number of complimentary remote sensing techniques exist. In the auroral zone ground-based photometers have been sued to monitor, at night, variations of the column O/N2 at a single location as a function of time. Satellite observations (most notably the GUVI instrument on TIMED) provide column O/N2 variations during the daytime as a function of latitude at a nearly fixed local time. Rockets have recently been shown to be able to measure vertical variations in an auroral arc providing altitude-based measurements. Here we review some of the most recent results with an emphasis on comparison with the model predictions of MSIS.

  7. Meso-scale aurora within the expansion phase bulge

    Directory of Open Access Journals (Sweden)

    N. Partamies

    2006-09-01

    Full Text Available We present ground-based optical, riometer and magnetometer recordings together with Polar UVI and GOES magnetic field observations of a substorm that occurred over Canada on 24 November 1997. This event involved a clear optical onset followed by poleward motion of the aurora as a signature of an expanding auroral bulge. During the expansion phase, there were three distinct types of meso-scale (10–1000 km auroral structures embedded in the bulge: at first a series of equatorward moving auroral arcs, followed by a well-defined spiral pair, and finally north-south directed aurora (a streamer. The spirals occurred several minutes after the onset, and indicate a shear in the field-aligned current. The north-south aligned aurora that formed about 10 min after the onset suggest bursty bulk flow type flows taking place in the central plasma sheet. Polar UVI observations of the polar cap location indicate that the southward drifting arcs were associated with magnetospheric activity within closed field lines, while the auroral streamer was launched by the bulge reaching the polar cap boundary, i.e. the mid-tail reconnection starting on the open field lines. The riometer data imply high energy electron precipitation in the vicinity of the the poleward moving edge of the auroral bulge, starting at the onset and continuing until the formation of the north-south structure. In this paper, we examine this evolving auroral morphology within the context of substorm theories.

  8. Forecasting auroras from regional and global magnetic field measurements

    Science.gov (United States)

    Kauristie, Kirsti; Myllys, Minna; Partamies, Noora; Viljanen, Ari; Peitso, Pyry; Juusola, Liisa; Ahmadzai, Shabana; Singh, Vikramjit; Keil, Ralf; Martinez, Unai; Luginin, Alexej; Glover, Alexi; Navarro, Vicente; Raita, Tero

    2016-06-01

    We use the connection between auroral sightings and rapid geomagnetic field variations in a concept for a Regional Auroral Forecast (RAF) service. The service is based on statistical relationships between near-real-time alerts issued by the NOAA Space Weather Prediction Center and magnetic time derivative (dB/dt) values measured by five MIRACLE magnetometer stations located in Finland at auroral and sub-auroral latitudes. Our database contains NOAA alerts and dB/dt observations from the years 2002-2012. These data are used to create a set of conditional probabilities, which tell the service user when the probability of seeing auroras exceeds the average conditions in Fennoscandia during the coming 0-12 h. Favourable conditions for auroral displays are associated with ground magnetic field time derivative values (dB/dt) exceeding certain latitude-dependent threshold values. Our statistical analyses reveal that the probabilities of recording dB/dt exceeding the thresholds stay below 50 % after NOAA alerts on X-ray bursts or on energetic particle flux enhancements. Therefore, those alerts are not very useful for auroral forecasts if we want to keep the number of false alarms low. However, NOAA alerts on global geomagnetic storms (characterized with Kp values > 4) enable probability estimates of > 50 % with lead times of 3-12 h. RAF forecasts thus rely heavily on the well-known fact that bright auroras appear during geomagnetic storms. The additional new piece of information which RAF brings to the previous picture is the knowledge on typical storm durations at different latitudes. For example, the service users south of the Arctic Circle will learn that after a NOAA ALTK06 issuance in night, auroral spotting should be done within 12 h after the alert, while at higher latitudes conditions can remain favourable during the next night.

  9. On the motion of dayside auroras caused by a solar wind pressure pulse

    Directory of Open Access Journals (Sweden)

    A. Kozlovsky

    2005-02-01

    Full Text Available Global ultraviolet auroral images from the IMAGE satellite were used to investigate the dynamics of the dayside auroral oval responding to a sudden impulse (SI in the solar wind pressure. At the same time, the TV all-sky camera and the EISCAT radar on Svalbard (in the pre-noon sector allowed for detailed investigation of the auroral forms and the ionospheric plasma flow. After the SI, new discrete auroral forms appeared in the poleward part of the auroral oval so that the middle of the dayside oval moved poleward from about 70° to about 73° of the AACGM latitude. This poleward shift first occurred in the 15 MLT sector, then similar shifts were observed in the MLT sectors located more westerly, and eventually the shift was seen in the 6 MLT sector. Thus, the auroral disturbance "propagated" westward (from 15 MLT to 6 MLT at an apparent speed of the order of 7km/s. This motion of the middle of the auroral oval was caused by the redistribution of the luminosity within the oval and was not associated with the corresponding motion of the poleward boundary of the oval. The SI was followed by an increase in the northward plasma convection velocity. Individual auroral forms showed poleward progressions with velocities close to the velocity of the northward plasma convection. The observations indicate firstly a pressure disturbance propagation through the magnetosphere at a velocity of the order of 200km/s which is essentially slower than the velocity of the fast Alfvén (magnetosonic wave, and secondly a potential (curl-free electric field generation behind the front of the propagating disturbance, causing the motion of the auroras. We suggest a physical explanation for the slow propagation of the disturbance through the magnetosphere and a model for the electric field generation. Predictions of the model are supported by the global convection maps produced by the SuperDARN HF radars. Finally, the interchange instability and the eigenmode toroidal

  10. Dayside aurora and the role of IMF ∣By∣/∣Bz∣: detailed morphology and response to magnetopause reconnection

    Directory of Open Access Journals (Sweden)

    W. F. Denig

    2004-01-01

    Full Text Available We document the detailed spatio-temporal structure of the dayside aurora during intervals of ongoing dayside magnetopause reconnection, primarily during interplanetary magnetic field (IMF Bz≤0 conditions. The present study is based on ground auroral observations in combination with particle precipitation data from a DMSP spacecraft. We describe auroral forms corresponding to the following particle precipitation regimes identified by Newell and Meng (1994: (i central plasma sheet (CPS, (ii precipitation void, (iii dayside boundary plasma sheet (BPS, and (iv cusp (LLBL/cusp/mantle. Two distinctly different auroral configurations are observed, corresponding to different regimes of the IMF clock angle (θ and the ∣By∣/∣Bz∣ ratio. Two regimes are defined. In regime (I θ lies within ∼ 90–135° and ∣By∣/∣Bz∣>1 (By-dominated, while in regime (II θ is in the range 135°–180° and ∣By∣/∣Bz∣Bz-dominated. Within regime (I the auroral response to reconnection events typically progresses from lower to higher latitudes in stages as indicated below: (A equatorward boundary intensifications (EBIs: sequential brightenings of closely spaced, fragmented, rayed bands (BPS aurora within the ∼08:00–15:00 MLT sector, each of which are moving noonward/sunward, (B poleward moving auroral forms (PMAFs: forms expanding westward from the postnoon side (By>0 and later appearing as a poleward expanding form in the convection throat in the ∼09:00–12:00 MLT sector, with a fading phase in the regime of mantle precipitation. During strongly southward IMF conditions (regime II, the intense PMAF activity is replaced by a more latitudinally restricted, but longitudinally wide aurora of moderate intensity. The latter auroral state is accompanied by a 2-cell convection pattern which is rather symmetrical about noon. This state is very different from the convection/FAC configuration present during IMF regime (I, with its strong zonal flows

  11. Estimating some parameters of the equatorial ionosphere electrodynamics from ionosonde data in West Africa

    Science.gov (United States)

    Grodji, F. O.; Doumbia, V.; Boka, K.; Amory-Mazaudier, C.; Cohen, Y.; Fleury, R.

    2017-01-01

    During the International Equatorial Electrojet Year (IEEY), an IPS-42 ionosonde located at Korhogo (9.33°N, 5.42°W, -1.88° dip-lat) and a meridian chain of 10 magnetic stations were setup in West Africa (5°West longitude). In this work, some characteristic parameters of the equatorial electrojet were estimated on the basis of the IPS-42 ionosonde data at Korhogo during the years 1993 and 1994. The study consisted of determining the zonal electric field through an estimate of the plasma vertical drift velocity. The daytime plasma vertical drift velocity was estimated from the time rates of change of the F-layer virtual height variations and a correction term that takes into account the ionization production and recombination effects. This method resulted in an improved vertical drift velocity, which was found to be comparable to the results of previous studies. The estimated vertical drift velocity was used in a semi-empirical approach which involved the IRI-2012 model for the Pedersen and Hall conductivities and the IGRF-10 model for the geomagnetic main field intensity. Thus the zonal and polarization electric fields on one hand, and the eastward Pedersen, Hall and the equatorial electrojet current densities on the other hand, were estimated. Furthermore the integrated peak current density at the EEJ center was estimated from ionosonde observations and compared with that inferred from magnetometer data. The integrated EEJ peak current densities obtained from both experiments were found to be in the same order and their seasonal variations exhibit the same trends as well.

  12. The Relationship of Magnetotail Flow Bursts and Ground Onset Signatures

    Science.gov (United States)

    Kepko, Larry; Spanswick, Emma; Angelopoulos, Vassilis; Donovan, Eric

    2010-01-01

    It has been known for decades that auroral substorm onset occurs on (or at least near) the most equatorward auroral arc, which is thought to map to the near geosynchronous region. The lack of auroral signatures poleward of this arc prior to onset has been a major criticism of flow-burst driven models of substorm onset. The combined THEMIS 5 spacecraft in-situ and ground array measurements provide an unprecedented opportunity to examine the causal relationship between midtail plasma flows, aurora, and ground magnetic signatures. I first present an event from 2008 using multi-spectral all sky imager data from Gillam and in-situ data from THEMIS. The multispectral data indicate an equatorward moving auroral form prior to substorm onset. When this forms reaches the most equatorward arc, the arc brightens and an auroral substorm begins. The THEMIS data show fast Earthward flows prior to onset as well. I discuss further the association of flow bursts and Pi2 pulsations, in the con text of the directly-driven Pi2 model. This model directly links flows and Pi2 pulsations, providing an important constraint on substorm onset theories.

  13. Dynamic rayed aurora and enhanced ion-acoustic radar echoes

    Directory of Open Access Journals (Sweden)

    E. M. Blixt

    2005-01-01

    Full Text Available The generation mechanism for naturally enhanced ion-acoustic echoes is still debated. One important issue is how these enhancements are related to auroral activity. All events of enhanced ion-acoustic echoes observed simultaneously with the EISCAT Svalbard Radar (ESR and with high-resolution narrow field-of-view auroral imagers have been collected and studied. Characteristic of all the events is the appearance of very dynamic rayed aurora, and some of the intrinsic features of these auroral displays are identified. Several of these identified features are directly related to the presence of low energy (10-100eV precipitating electrons in addition to the higher energy population producing most of the associated light. The low energy contribution is vital for the formation of the enhanced ion-acoustic echoes. We argue that this type of aurora is sufficient for the generation of naturally enhanced ion-acoustic echoes. In one event two imagers were used to observe the auroral rays simultaneously, one from the radar site and one 7km away. The data from these imagers shows that the auroral rays and the strong backscattering filaments (where the enhanced echoes are produced are located on the same field line, which is in contrast to earlier statements in the litterature that they should be separated.

  14. Concurrent observations of ultraviolet aurora and energetic electron precipitation with Mars Express

    Science.gov (United States)

    Gérard, J.-C.; Soret, L.; Libert, L.; Lundin, R.; Stiepen, A.; Radioti, A.; Bertaux, J.-L.

    2015-08-01

    The database of the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument between late January 2004 and Mars 2014 has been searched to identify signatures of CO Cameron and CO2+ doublet ultraviolet auroral emissions. This study has almost doubled the number of auroral detections based on SPICAM spectra. Auroral emissions are located in the vicinity of the statistical boundary between open and closed field lines. From a total of 113 nightside orbits with SPICAM pointing to the nadir in the region of residual magnetic field, only nine nightside orbits show confirmed auroral signatures, some with multiple detections along the orbital track, leading to a total of 16 detections. The mean energy of the electron energy spectra measured during concurrent Analyzer of Space Plasma and Energetic Atoms/Electron Spectrometer observations ranges from 150 to 280 eV. The ultraviolet aurora may be displaced poleward or equatorward of the region of enhanced downward electron energy flux by several tens of seconds and shows no proportionality with the electron flux at the spacecraft altitude. The absence of further UV auroral detection in regions located along crustal magnetic field structures where occasional aurora has been observed indicates that the Mars aurora is a time-dependent feature. These results are consistent with the scenario of acceleration of electrons by transient parallel electric field along semiopen magnetic field lines.

  15. An autonomous receiver/digital signal processor applied to ground-based and rocket-borne wave experiments

    Science.gov (United States)

    Dombrowski, M. P.; LaBelle, J.; McGaw, D. G.; Broughton, M. C.

    2016-07-01

    The programmable combined receiver/digital signal processor platform presented in this article is designed for digital downsampling and processing of general waveform inputs with a 66 MHz initial sampling rate and multi-input synchronized sampling. Systems based on this platform are capable of fully autonomous low-power operation, can be programmed to preprocess and filter the data for preselection and reduction, and may output to a diverse array of transmission or telemetry media. We describe three versions of this system, one for deployment on sounding rockets and two for ground-based applications. The rocket system was flown on the Correlation of High-Frequency and Auroral Roar Measurements (CHARM)-II mission launched from Poker Flat Research Range, Alaska, in 2010. It measured auroral "roar" signals at 2.60 MHz. The ground-based systems have been deployed at Sondrestrom, Greenland, and South Pole Station, Antarctica. The Greenland system synchronously samples signals from three spaced antennas providing direction finding of 0-5 MHz waves. It has successfully measured auroral signals and man-made broadcast signals. The South Pole system synchronously samples signals from two crossed antennas, providing polarization information. It has successfully measured the polarization of auroral kilometric radiation-like signals as well as auroral hiss. Further systems are in development for future rocket missions and for installation in Antarctic Automatic Geophysical Observatories.

  16. Considerations of variations in ionospheric field effects in mapping equatorial lithospheric Magsat magnetic anomalies

    Science.gov (United States)

    Ravat, D.; Hinze, W. J.

    1993-01-01

    The longitudinal, seasonal, and altitude-dependent variability of the magnetic field in equatorial latitudes is investigated to determine the effect of these variabilities on the isolation of lithospheric Magsat magnetic anomalies. It was found that the amplitudes of the dawn dip-latitude averages were small compared to the dusk averages, and that they were of the opposite sign. The longitudinal variation in the equatorial amplitudes of the dawn dip-latitude averages was not entirely consistent with the present knowledge of the electrojet field. Based on the results, a procedure is implemented for reducing the equatorial ionospheric effects from the Magsat data on the lithospheric component.

  17. Optimization methods of near-Earth and interplanetary flights with low thrust

    Science.gov (United States)

    Salmin, V. V.; Starinova, O. L.; Volosuev, V. V.; Petrukhina, K. V.; Tkachenko, I. S.; Chetverikov, A. S.

    2017-01-01

    The problem of improving the efficiency of space transport operations and control modes of the orbits of spacecraft now is particularly relevant. One possible solution of this problem is the use of propulsion systems on the basis of the low-thrust electro-jet engines. Authors provides methods for the design-ballistic optimization of space missions. The optimization problem is divided into two independent: dynamic - is finding the optimal control programs; parametric - finding the optimal design parameters of the spacecraft and ballistic mission parameters.

  18. Aurorasaurus: A citizen science platform for viewing and reporting the aurora

    Science.gov (United States)

    MacDonald, E. A.; Case, N. A.; Clayton, J. H.; Hall, M. K.; Heavner, M.; Lalone, N.; Patel, K. G.; Tapia, A.

    2015-09-01

    A new, citizen science-based, aurora observing and reporting platform has been developed with the primary aim of collecting auroral observations made by the general public to further improve the modeling of the aurora. In addition, the real-time ability of this platform facilitates the combination of citizen science observations with auroral oval models to improve auroral visibility nowcasting. Aurorasaurus provides easily understandable aurora information, basic gamification, and real-time location-based notification of verified aurora activity to engage citizen scientists. The Aurorasaurus project is one of only a handful of space weather citizen science projects and can provide useful results for the space weather and citizen science communities. Early results are promising with over 2000 registered users submitting over 1000 aurora observations and verifying over 1700 aurora sightings posted on Twitter.

  19. Multi-spectral simultaneous diagnosis of Saturns aurorae throughout a planetary rotation

    CERN Document Server

    Lamy, L; Pryor, W; Gustin, J; Badman, S V; Melin, H; Stallard, T; Mitchell, D G; Brandt, P C

    2013-01-01

    From the 27th to the 28th January 2009, the Cassini spacecraft remotely acquired combined observations of Saturns southern aurorae at radio, ultraviolet and infrared wavelengths, while monitoring ion injections in the middle magnetosphere from energetic neutral atoms. Simultaneous measurements included the sampling of a full planetary rotation, a relevant timescale to investigate auroral emissions driven by processes internal to the magnetosphere. In addition, this interval coincidently matched a powerful substorm-like event in the magnetotail, which induced an overall dawnside intensification of the magnetospheric and auroral activity. We comparatively analyze this unique set of measurements to reach a comprehensive view of kronian auroral processes over the investigated timescale. We identify three source regions in atmospheric aurorae, including a main oval associated with the bulk of Saturn Kilometric Radiation (SKR), together with polar and equatorward emissions. These observations reveal the co-existenc...

  20. Hyperspectral all-sky imaging of auroras.

    Science.gov (United States)

    Sigernes, Fred; Ivanov, Yuriy; Chernouss, Sergey; Trondsen, Trond; Roldugin, Alexey; Fedorenko, Yury; Kozelov, Boris; Kirillov, Andrey; Kornilov, Ilia; Safargaleev, Vladimir; Holmen, Silje; Dyrland, Margit; Lorentzen, Dag; Baddeley, Lisa

    2012-12-03

    A prototype auroral hyperspectral all-sky camera has been constructed and tested. It uses electro-optical tunable filters to image the night sky as a function of wavelength throughout the visible spectrum with no moving mechanical parts. The core optical system includes a new high power all-sky lens with F-number equal to f/1.1. The camera has been tested at the Kjell Henriksen Observatory (KHO) during the auroral season of 2011/2012. It detects all sub classes of aurora above ~½ of the sub visual 1kR green intensity threshold at an exposure time of only one second. Supervised classification of the hyperspectral data shows promise as a new method to process and identify auroral forms.