WorldWideScience

Sample records for auroral substorms

  1. 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...

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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...

  7. 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....

  8. 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.

  9. 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.

  10. 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...

  11. 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

  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. 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.

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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...

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. Chapman Conference: Magnetospheric Substorms

    Science.gov (United States)

    Iijima, Takesi; Kokubun, Susumu; Kan, Joseph R.; Potemra, T. A.

    Magnetospheric substorms are characterized by fascinating auroral displays in the ionosphere and by complex plasma dynamics in the magnetotail. The complicated plasma processes associated with substorms fascinated space researchers even before the space age, when observations were limited to the Earth's surface. These processes are believed to be fundamentally important to plasma physics, and also to apply to solar flares and other cosmic phenomena. Substorms have been the focus of intense study and controversy within space science for several decades.

  6. 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

  7. Onset of magnetospheric substorms.

    Science.gov (United States)

    Tsurutani, B.; Bogott, F.

    1972-01-01

    An examination of the onset of magnetospheric substorms is made by using ATS 5 energetic particles, conjugate balloon X rays and electric fields, all-sky camera photographs, and auroral-zone magnetograms. It is shown that plasma injection to ATS distances, conjugate 1- to 10-keV auroral particle precipitation, energetic electron precipitation, and enhancements of westward magnetospheric electric-field component all occur with the star of slowly developing negative magnetic bays. No trapped or precipitating energetic-particle features are seen at ATS 5 when later sharp negative magnetic-bay onsets occur at Churchill or Great Whale River.

  8. 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.

  9. THEMIS observations of two substorms on February 26,2008

    Institute of Scientific and Technical Information of China (English)

    V; MISHIN; V; ANGELOPOULOS; K; H; GLASSMEIER; J; MCFADDEN; D; LARSON; S; MENDE; USAH; FREY; C; T; RUSSELL; I; MANN; D; SIBECK; T; I; SAIFUDINOVA; M; V; TOLOCHKO; L; A; SAPRONOVA; H; REME; E; LUCEK

    2010-01-01

    Two substorms occurred at ~04:05 and ~04:55 UT on February 26,2008 are studied with the in-situ observations of THEMIS satellites and ground-based aurora and magnetic field measurements.Angelopoulos et al.have made a comprehensive study of the 04:55 UT event.We showed detailed features of the two substorms with much attention to the first event and to the rela-tionship between mid-tail magnetic reconnection(MR) and substorm activities.It was found that in the earlier stage of each substorm,a first auroral intensification occurred 2-3 min soon after the start of mid-tail MR,followed by a slow and very lim-ited expansion.The auroral arcs were weak,short-lived,and localized,characterizing all features of a pseudobreakup.We re-garded the first auroral brightening as the initial onset of the substorms.A few minutes later,a second stronger auroral intensification appeared,followed by quick and extensive expansions.It was interesting to note that the second brightening and related poleward expansion happened almost simultaneously(within a couple of minutes) with the onset of earthward flow and dipolarization in the near-Earth tail and other phenomenon of the substorm expansion phase.We thus regarded the second auroral brightening as the major onset of the substorms.Furthermore,it was seen that during the growth phase of the two substorms,the polar cap open flux Ψ kept increasing,while it quickly reduced during the substorm expansion and recovery phase.These variations of Ψ implied that the evolution of the two substorm expansion phases were closely related to MR of tail lobe open field lines.Analysis of substorm activities revealed that the two events studied were small substorms;while estimate of MR rate indicated that the MR processes in the two substorms were weak.The aforementioned observations suggested that mid-tail MR initiated the pseudobreakup first;the earthward flow generated by MR transported magnetic flux and energy to the near-Earth tail to cause the

  10. 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

  11. 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.

  12. A multipoint study of a substorm occurring on 7 December, 1992, and its theoretical implications

    DEFF Research Database (Denmark)

    Fox, N.J.; Cowley, S.W.H.; Davda, V.N.

    1999-01-01

    array in Scandinavia and the two Greenland chains, the auroral distribution observed by Freja and the substorm cycle observations by the SABRE radar, the SAMNET magnetometer array and LANL geosynchronous satellites. Data from Galileo Earth-encounter II are used to estimate the IMF B-z component...... a subsequent substorm intensification 25 min after the initial onset. After this time, the substorm auroral bulge in the nightside hours propagated well poleward of the pre-existing convection reversal boundary, and strong flow perturbations were observed by the Goose Bay radar, indicative of flows driven...

  13. 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...

  14. 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.

  15. 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.

  16. 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

  17. Response of high-energy particle precipitation to substorm onset

    Science.gov (United States)

    Kellerman, A. C.; Makarevich, R. A.

    2008-12-01

    The process of extra-terrestrial radiowave absorption by ionospheric electrons is known as cosmic noise absorption (CNA) and is routinely detected by ground-based relative opacity meters or riometers, which are sensitive to high-energy particle precipitation (>10 keV). In this study, we investigate the response of high- energy particle precipitation to substorm onset by employing a 7×7-beam imaging riometer system in Northern Scandinavia, IRIS, and the substorm onset database from the IMAGE satellite. The CNA response is investigated with respect to substorm location relative to IRIS. Instantaneous responses are mostly observed when IRIS is located on the same magnetic parallel as the substorm onset region. We investigate dispersionless injections (DIs) associated with substorm onsets as detected by the imaging riometer. It is shown that an auroral absorption signature is present predominantly for DIs located westward of IRIS, which is consistent with high-energy particles propagating eastward from substorm injection location. Superposed epoch analysis of CNA relative to substorm onset timing shows a strong dependence on the azimuthal sector in which the onset is located relative to IRIS. Rapid responses are observed in 90-135 deg geographic azimuths indicating fast westward and poleward propagation from onset location. Responses to onsets located between -90 to -180 deg show a monotonic decrease in rise time. The results are examined in the context of the geosynchronous LANL and GOES satellite data in order to investigate the two propagation mechanisms: expansion of injection region and particle drift.

  18. 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.

  19. Network analysis of geomagnetic substorms using the SuperMAG database of ground-based magnetometer stations

    CERN Document Server

    Dods, J; Gjerloev, J W

    2016-01-01

    The overall morphology and dynamics of magnetospheric substorms is well established in terms of the observed qualitative auroral features seen in ground-based magnetometers. This paper focuses on the quantitative characterization of substorm dynamics captured by ground-based magnetometer stations. We present the first analysis of substorms using dynamical networks obtained from the full available set of ground-based magnetometer observations in the Northern Hemisphere. The stations are connected in the network when the correlation between the vector magnetometer time series from pairs of stations within a running time window exceeds a threshold. Dimensionless parameters can then be obtained that characterize the network and by extension, the spatiotemporal dynamics of the substorm under observation. We analyze four isolated substorm test cases as well as a steady magnetic convection (SMC) event and a day in which no substorms occur. These test case substorms are found to give a consistent characteristic netwo...

  20. 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

  1. 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.

  2. Early MITHRAS results - The electric field response to substorms

    Science.gov (United States)

    de La Beaujardiere, O.; Holt, J.; Nielsen, E.

    1983-12-01

    The MITHRAS data base offers a unique opportunity to observe simultaneously the auroral-zone ion convection pattern with three radars, widely separated in longitude. It is attempted to separate local-time versus universal-time effects in a study of the electric field signature associated with substorms. Preliminary results indicate that this signature is similar at a given local time, regardless of the longitude of the station. In the dawn and dusk sectors the electric field is intensified, whereas around noon and midnight the electric field appears to reverse during a substorm. The potential drop across the polar cap can be estimated from the potential across the auroral oval. The radar data agree well with the relationship found by Reiff and co-workers between the solar wind energy parameter epsilon and the cross-tail potential.

  3. Early MITHRAS results - the electric field response to substorms

    Energy Technology Data Exchange (ETDEWEB)

    De La Beaujardiere, O.; Holt, J.; Nielsen, E.

    1983-11-01

    The MITHRAS data base offers a unique opportunity to observe simultaneously the auroral-zone ion convection pattern with three radars, widely separated in longitude. It is attempted to separate local-time versus universal-time effects in a study of the electric field signature associated with substorms. Preliminary results indicate that this signature is similar at a given local time, regardless of the longitude of the station. In the dawn and dusk sectors the electric field is intensified, whereas around noon and midnight the electric field appears to reverse during a substorm. The potential drop across the polar cap can be estimated from the potential across the auroral oval. The radar data agree well with the relationship found by Reiff and co-workers between the solar wind energy parameter epsilon and the cross-tail potential. 15 references.

  4. Early MITHRAS results: the electric field response to substorms

    Energy Technology Data Exchange (ETDEWEB)

    Beaujardiere, O.; Holt, J.; Nielsen, E.

    1983-12-01

    The MITHRAS data base offers a unique opportunity to observe simultaneously the auroral-zone ion-convection pattern with three radars, widely separated in longitude. The authors attempt to separate local-time versus universal-time effects in a study of the electric field signature associated with substorms. Preliminary results indicate that this signature is similar at a given local time, regardless of the longitude of the station. In the dawn and dusk sectors the electric field is intensified, whereas around noon and midnight the electric field appears to reverse during a substorm. The potential drop across the polar cap can be estimated from the potential across the auroral oval. The radar agree well with the relationship found by Reiff and co-workers between the solar wind energy parameter epsilon and the cross-tail potential.

  5. 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.

  6. Observational evidence for an inside-out substorm onset scenario

    Energy Technology Data Exchange (ETDEWEB)

    Henderson, Michael G [Los Alamos National Laboratory

    2008-01-01

    We present observations which provide strong support for a substorm onset scenario in which a localized inner magnetospheric instability developed first and was later followed by the development of a Near Earth Neutral Line (NENL) farther down-tail. Specifically, we find that the onset began as a localized brightening of an intensified growth phase arc which developed as a periodic series of arc-aligned (i.e. azimuthally arrayed) bright spots. As the disturbance grew, it evolved into vortical structures that propagated poleward and eventually morphed into an east-west aligned arc system at the poleward edge of the auroral substorm bulge. The auroral intensification shows an exponential growth with an estimated e-folding time of around 188 seconds (linear growth rate, {gamma} of 5.33 x 10{sup -3} s{sup -1}). During the initial breakup, no obvious distortions of auroral forms to the north were observed. However, during the expansion phase, intensifications of the poleward boundary of the expanding bulge were observed together with the equatorward ejection of auroral streamers into the bulge. A strong particle injection was observed at geosynchronous orbit, but was delayed by several minutes relative to onsel. Ground magnetometer data also shows a two phase development of mid-latitude positive H-bays, with a quasi-linear increase in H between the onset and the injection. We conclude that this event provides strong evidence in favor of the so-called 'inside-out' substorm onset scenario in which the near Earth region activates first followed at a later time by the formation of a near-to-mid tail substorm X-line. The ballooning instability is discussed as a likely mechanism for the initial onset.

  7. 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

  8. In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge

    DEFF Research Database (Denmark)

    Forsyth, C.; Fazakerley, A. N.; Rae, I. J.

    2014-01-01

    perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show...

  9. Conjunction of tail satellites for substorm study: ISTP event of 1997 January 2

    DEFF Research Database (Denmark)

    Lui, A.T.Y.; Liou, K.; Newell, P.T.;

    2000-01-01

    dipolarization at Geotail and highly fluctuating magnetic field (mostly northward B-z) at IMP-8. Observations for this substorm showed no indication of mid-tail activities occurring prior to auroral brightening for both onset and intensification even though the satellites observed activities subsequently. Close...

  10. Variations in the polar cap area during two substorm cycles

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available This study employs observations from several sources to determine the location of the polar cap boundary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified. These data sources include global auroral images from the Ultraviolet Imager (UVI instrument on board the Polar spacecraft, SuperDARN HF radar measurements of the convection flow, and low altitude particle measurements from Defense Meteorological Satellite Program (DMSP and National Oceanographic and Atmospheric Administration (NOAA satellites, and the Fast Auroral SnapshoT (FAST spacecraft. Changes in the open flux content of the magnetosphere are related to the rate of magnetic reconnection occurring at the magnetopause and in the magnetotail, allowing us to estimate the day- and nightside reconnection voltages during two substorm cycles. Specifically, increases in the polar cap area are found to be consistent with open flux being created when the IMF is oriented southwards and low-latitude magnetopause reconnection is ongoing, and decreases in area correspond to open flux being destroyed at substorm breakup. The polar cap area can continue to decrease for 100 min following the onset of substorm breakup, continuing even after substorm-associated auroral features have died away. An estimate of the dayside reconnection voltage, determined from plasma drift measurements in the ionosphere, indicates that reconnection can take place at all local times along the dayside portion of the polar cap boundary, and hence presumably across the majority of the dayside magnetopause. The observation of ionospheric signatures of bursty reconnection over a wide extent of local times supports this finding.

    Key words. Ionosphere (plasma convection; polar ionosphere – Magnetospheric physics (magnetospheric configuration and dynamics

  11. Global Observation of Substorm Growth Phase Processes in the Polar Caps

    Science.gov (United States)

    Brittnacher, M.; OFillingim, M. O.; Chua, D.; Wilber, M.; Parks, G. K.; Germany, G. A.; Spann, J. F.

    1998-01-01

    Global images of the polar cap region during the substorm growth phase by the Polar Ultraviolet Imager reveals evidence of the processes which are not completely explained by current models. In particular, it was found that size of the polar cap region increases during the growth phase even if the interplanetary magnetic field has no southward component. Three phenomena were observed to produce an increase in the size of the polar cap: (1) motion of the auroral oval to lower latitude, (2) thinning of the auroral oval, and (3) reduction of intense aurora[ precipitation in the polar region. Correlation of image intensities with in situ particle measurements from the FAST satellite are being conducted to study the three growth phase phenomena; and to help identify the source regions of the particles, the mechanisms involved in producing the auroral structures and what may be reducing the polar cap precipitation during the substorm growth phase.

  12. 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.

  13. Pressure Gradient Evolution and Substorm Onset

    Science.gov (United States)

    Zhonghua, Y.; Pu, Z.; Cao, X.; Nishimura, T.; Zhang, H.; Fu, S.; Xie, L.; Guo, R.

    2011-12-01

    Near-Earth current disruption (NECD) and substorm current wedge (SCW) formation are two related key phenomena for substorm onset. They are believed to be in close association with evolution of pressure gradient near the inner edge of plasma sheet. In the past, a few attempts have been made to investigate the pressure gradient in the late growth phase based on one- or two-spacecraft observations (e.g. , Korth et al., 1991; Pu et al., 1992; Shiokawa et al., 1998; Xing et al., 2010, 2011,etc). In this paper, with linearization assumption in the inner-probe region, we use THEMIS three-probe measurements to estimate the pressure gradient near the inner edge of the equatorward and duskward (dawnward) plasma sheet where pressure gradient in the Z-direction is almost vanished. We therefore can roughly get the two-dimensional pressure gradient in the X- and Y-direction simultaneously. Our observations indicate that the pressure gradients in both the X- and Y-direction enhance right after (within one minute) substorm onset. The enhanced pressure gradient in the Y-direction is duskward (dawnward) when the probes are in the duskside (dawnside) of the enhanced earthward flow in the growth phase. The enhanced dawn-dusk pressure gradients can drive downward field-aligned current (FAC) on the dawnside and upward FAC on the duskside, thus make contributions to the NECD and formation of SCW. THEMIS in situ data and all-sky auroral images for two events are presented, followed by a brief discussion.

  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. 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...

  16. Dynamics of the outer radiation belts in relation to polar substorms and hot plasma injections at geostationary altitude

    Science.gov (United States)

    Sauvaud, J. A.; Winckler, J. R.

    1981-01-01

    Geostationary satellite and ground measurements of dynamic variations of the outer radiation belts and their relations with the development of auroral structures during magnetospheric substorms are analyzed. A comparison of measurements of the H or X geomagnetic field components made by seven auroral stations with ATS-6 low-energy and high-energy particle measurements during the multiple-onset substorm of Aug. 16, 1974 is presented which demonstrates that while the decrease in energetic particle fluxed ends only at the time of a strong substorm onset, rapid motions of the outer radiation belts may occur during the flux decrease. All-sky photographs of auroral phenomena taken at Fort Yukon and College, Alaska are then compared with ATS-1 energetic particle flux measurements in order to demonstrate the relation between flux decreases and increases and distinct substorm phases. Results support the hypothesis of a magnetospheric substorm precursor which appears to be an instability growing at the inner boundary of the plasma layer and approaching the earth, and underline the importance of current and magnetic field variations in charged particle dynamics.

  17. 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.

  18. The Influence of Temperature Anisotropies in Controlling the Development of Magnetospheric Substorms

    CERN Document Server

    Winglee, Robert

    2016-01-01

    Ion anisotropies can affect a host of processes within the magnetosphere, from modifying the growth rate of various instabilities to the energization and mass transport within the magnetosphere. Global multi-fluid simulations using a full treatment of the pressure tensor are used to evaluate the influence of temperature anisotropies on the magnetospheric dynamics for an idealized substorm. The simulations are able to resolve the development of conics over the polar cap which eventually turn into beams in the lobes. Entry of this plasma, particularly heavy ions with high Tparallel, leads to a faster reconnection rate, additional turbulence within the reconnection region, and the substorm onset time occurs approximately 5 min earlier relative to isotropic simulations. The anisotropic treatment yields much more intense auroral currents on the nightside associated with onset and a faster expansion phase of the substorm. The plasma entering into the current sheet experiences stronger heating in the anisotropic sim...

  19. 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.

  20. 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

  1. 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.

  2. The substorm event of 28 January 1983: a detailed global study

    Energy Technology Data Exchange (ETDEWEB)

    Baker, D.N.; Fairfield, D.H.; Slavin, J.A. (National Aeronautics and Space Administration, Greenbelt, MD (USA). Goddard Space Flight Center) (and others)

    1990-12-01

    A small, isolated substorm with an expansion phase onset at 07:39 U.T. ({plus minus}1 min) on 28 January 1983 was well observed by ground-based instrumentation as well as by low- and high-altitude spacecraft. This event period was chosen as a detailed analysis interval because of the comprehensive nature of the data coverage, and because ISEE-3 identified signatures within the distant tail ({approx}220 R{sub E}) following the substorm onset which has been interpreted as those of a plasmoid passage. In this paper we provide a comprehensive timeline of the growth, expansion, and recovery phases of the substorm. The magnetospheric energy input rates are evaluated using IMP-8 in the upstream solar wind. For the first time, DE-1 imaging sequences are used to examine auroral features during the growth and expansion phases while ISEE-3 was in the deep tail. Substorm current wedge location and expansion onset information was provided by ground-based magnetometer and geostationary orbit (particle and magnetic field) data. The plasma, energetic particle, and field signatures at ISEE-3 are considered within the framework of the near-Earth data sets. We quantitatively estimate substorm energy input and output relationships for this case and we evaluate the timing and physical dimensions of the distant tail disturbance implied by the global observations available. Overall, the present analysis provides a thorough documentation of a substorm to an unprecedented degree; most of the data support the developing paradigm of the near-Earth neutral line and plasmoid formation model. We also consider the boundary layer dynamics model of substorms as an alternative explanation of the global magnetospheric phenomena in this event, but as presented this model does not provide a superior organisation of the available data sets. (author).

  3. 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

  4. Magnetic reconnection during magnetospheric substorms

    Science.gov (United States)

    Baker, Daniel N.

    1996-01-01

    The near earth reconnection model of substorms represents an attempt to place a broad range of observations into a consistent framework. The roles and requirements of reconnection are discussed. High speed plasma sheet flows, thin current sheet instability, substorm triggering, plasmoids and flux ropes in the distant tail, and magnetohydrodynamic simulations are discussed. Substorms are global, coherent sequences of processes involving solar wind/magnetosphere/ionosphere interaction. Magnetic reconnection is required to explain different dayside and polar cap phenomena, which required nightside reconnection. The modification and expansion of the standard near earth neutral line (NENL) model can integrate breakup arcs, current disruption, current wedge features, and localized plasma flows into the magnetic reconnection framework.

  5. Correlation between convection electric fields in the nightside magnetosphere and several wave and particle phenomena during two isolated substorms.

    Science.gov (United States)

    Carpenter, D. L.; Fraser-Smith, A. C.; Unwin, R. S.; Hones, E. W., Jr.; Heacock, R. R.

    1971-01-01

    Correlation of several magnetoionospheric wave and particle phenomena previously linked observationally to magnetospheric substorms and inferred to involve convection electric fields with whistler measurements of convection activity during two relatively isolated substorms. The events occurred at about 0600 UT on July 15, 1965, and about 0500 UT on Oct. 13, 1965. The correlated phenomena include cross-L inward plasma drifts near midnight within the plasmaphere, diffuse auroral radar echoes observed near the dusk meridian, IPDP micropulsations (intervals of pulsations of diminishing period) in the premidnight sector, apparent contractions and expansions of the plasma sheet at about 20 earth radii in the magnetotail, and Pc 1/Pi 1 micropulsation events near or before midnight. Two new vlf phenomena occurred during the October 13 event - a noise band within the plasmasphere associated with a convecting whistler path, and ?hisslers,' falling-tone auroral-hiss forms repeated at intervals of about 2 sec.

  6. 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

  7. A simulation study of the thermosphere mass density response to substorms using GITM

    Science.gov (United States)

    Liu, Xianjing; Ridley, Aaron

    2015-09-01

    The temporal and spatial variations of the thermospheric mass density during a series of idealized substorms were investigated using the Global Ionosphere Thermosphere Model (GITM). The maximum mass density perturbation of an idealized substorm with a peak variation of hemispheric power (HP) of 50 GW and interplanetary magnetic field (IMF) Bz of -2 nT was ~14% about 50 min after the substorm onset in the nightside sector of the auroral zone. The mass density response to different types of energy input has a strong local time dependence, with the mass density perturbation due to only an IMF Bz variation peaking in the dusk sector and the density perturbation due to only HP variation peaks in the nightside sector. Simulations with IMF Bz changes only and HP changes only showed that the system behaves slightly nonlinearly when both IMF and HP variations are included (a maximum of 6% of the nonlinearity) and that the nonlinearity grows with energy input. The neutral gas heating rate due to Joule heating was of same magnitude as the heating rate due to precipitation, but the majority of the temperature enhancement due to the heating due to precipitation occurs at lower altitude as compared to the auroral heating. About 110 min after onset, a negative mass density perturbation (~-5%) occurred in the night sector, which was consistent with the mass density measurement of the CHAMP satellite.

  8. 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.

  9. Flux closure during a substorm observed by Cluster, Double Star, IMAGE FUV, SuperDARN, and Greenland magnetometers

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    2006-03-01

    Full Text Available We examine magnetic flux closure during an extended substorm interval on 29 August 2004 involving a two-stage onset and subsequent re-intensifications. Cluster and Double Star provide observations of magnetotail dynamics, while the corresponding auroral evolution, convection response, and substorm current wedge development are monitored by IMAGE FUV, SuperDARN, and the Greenland magnetometer chain, respectively. The first stage of onset is associated with the reconnection of closed flux in the plasma sheet; this is accompanied by a short-lived auroral intensification, a modest substorm current wedge magnetic bay, but no significant ionospheric convection enhancement. The second stage follows the progression of reconnection to the open field lines of the lobes; accompanied by prolonged auroral bulge and westward-travelling surge development, enhanced magnetic bays and convection. We find that the tail dynamics are highly influenced by ongoing dayside creation of open flux, leading to flux pile-up in the near-tail and a step-wise down-tail motion of the tail reconnection site. In all, 5 dipolarizations are observed, each associated with the closure of ~0.1 GWb of flux. Very simple calculations indicate that the X-line should progress down-tail at a speed of 20 km s-1, or 6 RE between each dipolarization.

  10. 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.

  11. 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

  12. 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

  13. Different Alfvén wave acceleration processes of electrons in substorms at ~4-5 RE and 2-3 RE radial distance

    Directory of Open Access Journals (Sweden)

    J. C. Samson

    2004-06-01

    Full Text Available Recent statistical studies show the existence of an island of cavities and enhanced electric field structures at 4-5RE radial distance in the evening and midnight magnetic local time (MLT sectors in the auroral region during disturbed conditions, as well as ion beam occurrence frequency changes at the same altitude. We study the possibility that the mechanism involved is electron Landau resonance with incoming Alfvén waves and study the feasibility of the idea further with Polar electric field, magnetic field, spacecraft potential and electron data in an event where Polar maps to a substorm over the CANOPUS magnetometer array. Recently, a new type of auroral kilometric radiation (AKR emission originating from ~2-3RE radial distance, the so-called dot-AKR emission, has been reported to occur during substorm onsets and suggested to also be an effect of Alfvénic wave acceleration in a pre-existing auroral cavity. We improve the analysis of the dot-AKR, giving it a unified theoretical handling with the high-altitude Landau resonance phenomena. The purpose of the paper is to study the two types of Alfvénic electron acceleration, acknowledging that they have different physical mechanisms, altitudes and roles in substorm-related auroral processes.

  14. 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.

  15. 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...

  16. 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

  17. A joint Cluster and ground-based instruments study of two magnetospheric substorm events on 1 September 2002

    Directory of Open Access Journals (Sweden)

    N. C. Draper

    2004-12-01

    Full Text Available We present a coordinated ground- and space-based multi-instrument study of two magnetospheric substorm events that occurred on 1 September 2002, during the interval from 18:00 UT to 24:00 UT. Data from the Cluster and Polar spacecraft are considered in combination with ground-based magnetometer and HF radar data. During the first substorm event the Cluster spacecraft, which were in the Northern Hemisphere lobe, are to the west of the main region affected by the expansion phase. Nevertheless, substorm signatures are seen by Cluster at 18:25 UT (just after the expansion phase onset as seen on the ground at 18:23 UT, despite the ~5 RE} distance of the spacecraft from the plasma sheet. The Cluster spacecraft then encounter an earthward-moving diamagnetic cavity at 19:10 UT, having just entered the plasma sheet boundary layer. The second substorm expansion phase is preceded by pseudobreakups at 22:40 and 22:56 UT, at which time thinning of the near-Earth, L=6.6, plasma sheet occurs. The expansion phase onset at 23:05 UT is seen simultaneously in the ground magnetic field, in the magnetotail and at Polar's near-Earth position. The response in the ionospheric flows occurs one minute later. The second substorm better fits the near-Earth neutral line model for substorm onset than the cross-field current instability model.

    Key words. Magnetospheric physics (Magnetosphereionosphere interactions; Magnetic reconnection; Auroral phenomenon

  18. 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.

  19. Substorm onset: Current sheet avalanche and stop layer

    Science.gov (United States)

    Haerendel, Gerhard

    2015-03-01

    A new scenario is presented for the onset of a substorm and the nature of the breakup arc. There are two main components, current sheet avalanche and stop layer. The first refers to an earthward flow of plasma and magnetic flux from the central current sheet of the tail, triggered spontaneously or by some unknown interaction with an auroral streamer or a suddenly appearing eastward flow at the end of the growth phase. The second offers a mechanism to stop the flow abruptly at the interface between magnetosphere and tail and extract momentum and energy to be partially processed locally and partially transmitted as Poynting flux toward the ionosphere. The stop layer has a width of the order of the ion inertial length. The different dynamics of the ions entering freely and the magnetized electrons create an electric polarization field which stops the ion flow and drives a Hall current by which flow momentum is transferred to the magnetic field. A simple formalism is used to describe the operation of the process and to enable quantitative conclusions. An important conclusion is that by necessity the stop layer is also highly structured in longitude. This offers a natural explanation for the coarse ray structure of the breakup arc as manifestation of elementary paths of energy and momentum transport. The currents aligned with the rays are balanced between upward and downward directions. While the avalanche is invoked for explaining the spontaneous substorm onset at the inner edge of the tail, the expansion of the breakup arc for many minutes is taken as evidence for a continued formation of new stop layers by arrival of flow bursts from the near-Earth neutral line. This is in line with earlier conclusions about the nature of the breakup arc. Small-scale structure, propagation speed, and energy flux are quantitatively consistent with observations. However, the balanced small-scale currents cannot constitute the substorm current wedge. The source of the latter must be

  20. Extremely Intense Magnetospheric Substorms : External Triggering? Preconditioning?

    Science.gov (United States)

    Tsurutani, Bruce; Echer, Ezequiel; Hajra, Rajkumar

    2016-07-01

    We study particularly intense substorms using a variety of near-Earth spacecraft data and ground observations. We will relate the solar cycle dependences of events, determine whether the supersubstorms are externally or internally triggered, and their relationship to other factors such as magnetospheric preconditioning. If time permits, we will explore the details of the events and whether they are similar to regular (Akasofu, 1964) substorms or not. These intense substorms are an important feature of space weather since they may be responsible for power outages.

  1. 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

  2. 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°.

  3. 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°.

  4. 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.

  5. EISCAT observations of unusual flows in the morning sector associated with weak substorm activity

    Directory of Open Access Journals (Sweden)

    N. J. Fox

    Full Text Available A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at ~0415 MLT contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (~0515 MLT with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is "pinched off", and present two alternative explanations in terms of (1 viscous and lobe circulation cells and (2 polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked "viscous-like" momentum transfer across the magnetopause.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. Is energy storage and release part of the substorm process?

    Science.gov (United States)

    Clauer, C. R.

    1981-01-01

    Models for magnetospheric substorms were considered. A modified model which includes the growth phase, a time interval prior to the onset of the expansion phase, during which energy was transferred from a solar wind to the magnetosphere and stored for subsequent release, is discussed. Evidence for energy storage in the tail prior to substorm expansion for both isolated and moderate substorm activity is reviewed.

  12. 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.

  13. Storm-Time Substorms and Sawtooth Events: Test for Substorm Models

    Science.gov (United States)

    Pulkkinen, T. I.; Tanskanen, E. I.; Reeves, G. D.; Donovan, E.; Singer, H. J.; Slavin, J. A.

    2005-12-01

    A substorm search engine is used to identify substorm onsets that occur during magnetic storms in the period 2001-2004. Each substorm is analyzed in detail using several parameters to classify the events. Peak amplitude of the substorm is defined from the AL-index. Existence and type of energetic particle injections are determined from the LANL energetic ion and electron data. Tail magnetic field measurements (GOES, Cluster, Geotail) are used to infer whether a thin current sheet was formed prior to the substorm onset. Latitudinal magnetometer chains (CANOPUS, IMAGE) are used to determine whether the main expansion direction was poleward or equatorward. Possible triggers for the onset and intensity of the driving electric field are identified from the solar wind and interplanetary magnetic field measurements (ACE, WIND). The goal of the study is to statistically examine to what extent the stormtime substorms show signatures typically associated classical non-storm substorms and to what extent the activity is characteristic only of storm periods. Furthermore, the goal is to identify the "sawtooth events" from the data set, and examine whether the activation characteristics differ from the other stormtime activations.

  14. 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.

  15. A Study of Multiple and Single Onset Substorms Selected Using GOES 10 Magnetic Field Data

    Science.gov (United States)

    Stoner, J. M.; Larson, R. B.; Erickson, K. N.; Engebretson, M. J.; Singer, H. J.

    2008-05-01

    A return to a more dipolar configuration of the magnetic field on the night side, near synchronous orbit, is one good indicator of a substorm expansion phase onset. Substorm expansion phase onsets for this study were selected by requiring a well-defined increase in the z-component of the magnetic field measured by the GOES 10 satellite. Event selection was subject to 2 restrictions: an increase in the z-component of the magnetic field greater than 10 nT in GSM coordinates and GOES 10 was located on the night side within 3 hours either side of local midnight during the months of August through November of the years 2000 through 2004. These time restrictions allowed for events selected using GOES 10 to be compared with events selected using the HYDRA electron flux instrument on the Polar satellite, as presented by Larson et al. [Fall 2007 AGU Meeting]. Of the 119 events selected using GOES 10, 9 events overlapped with this previous study. As expected, the 119 events closely correlated with ground-based auroral zone Pi2 data. Substorms were classified as either single or multiple onset, the latter being differentiated from the former by observing one or more subsequent Pi2 intensifications. The ratio of multiple onset to single onset substorms was found to be 2:1. Using ground-based Pi2 data it was found that in general the magnetic latitude of the initial onset of the multiple onset events was lower than the magnetic latitude of single onset events. Multiple onset events were found between 62 and 67 degrees and single onset events between 65 and 73 degrees, with single onset events being an average of one degree higher in latitude. Additionally, the time interval between Pi2 intensifications for multiple onset events was found to have a range of 9 to 30 minutes with an average of 19 minutes. The local time distribution of events used in this study corresponded to 63 percent of events occurring before local midnight. An analysis of the value of the z-component of the

  16. 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.

  17. 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...

  18. Magnetic local time, substorm, and particle precipitation-related variations in the behaviour of SuperDARN Doppler spectral widths

    Directory of Open Access Journals (Sweden)

    M. L. Parkinson

    2004-12-01

    Full Text Available Super Dual Auroral Radar Network (DARN radars often detect a distinct transition in line-of-sight Doppler velocity spread, or spectral width, from <50ms–1 at lower latitude to >200ms–1 at higher latitude. They also detect a similar boundary, namely the range at which ionospheric scatter with large spectral width suddenly commences (i.e. without preceding scatter with low spectral width. The location and behaviour of the spectral width boundary (SWB (and scatter boundary and the open-closed magnetic field line boundary (OCB are thought to be closely related. The location of the nightside OCB can be inferred from the poleward edge of the auroral oval determined using energy spectra of precipitating particles measured on board Defence Meteorology Satellite Program (DMSP satellites. Observations made with the Halley SuperDARN radar (75.5° S, 26.6° W, geographic; –62.0°Λ and the Tasman International Geospace Environment Radar (TIGER (43.4° S, 147.2° E; –54.5°Λ are used to compare the location of the SWB with the DMSP-inferred OCB during 08:00 to 22:00 UT on 1 April 2000. This study interval was chosen because it includes several moderate substorms, whilst the Halley radar provided almost continuous high-time resolution measurements of the dayside SWB location and shape, and TIGER provided the same in the nightside ionosphere. The behaviour of the day- and nightside SWB can be understood in terms of the expanding/contracting polar cap model of high-latitude convection change, and the behaviour of the nightside SWB can also be organised according to substorm phase. Previous comparisons with DMSP OCBs have proven that the radar SWB is often a reasonable proxy for the OCB from dusk to just past midnight (Chisham et al., 2004. However, the present case study actually suggests that the nightside SWB is often a better proxy for the poleward edge of Pedersen conductance enhanced by hot particle precipitation in the

  19. Statistical visualization of the Earth's magnetotail based on Geotail data and the implied substorm model

    Directory of Open Access Journals (Sweden)

    S. Machida

    2009-03-01

    Full Text Available We investigated the temporal and spatial development of the near-Earth magnetotail during substorms based on multi-dimensional superposed-epoch analysis of Geotail data. The start time of the auroral break-up (t=0 of each substorm was determined from auroral data obtained by the Polar and IMAGE spacecraft. The key parameters derived from the plasma, magnetic-field, and electric-field data from Geotail were sorted by their meridional X(GSM–Z(proxy coordinates.

    The results show that the Poynting flux toward the plasma-sheet center starts at least 10 min before the substorm onset, and is further enhanced at X~−12 RE (Earth radii around 4 min before the onset. Simultaneously, large-amplitude fluctuations occurred, and earthward flows in the central plasma sheet between X~−11 RE and X~−19 RE and a duskward flow around X=−10 RE were enhanced. The total pressure starts to decrease around X=−16 RE about 4 min before the onset of the substorm. After the substorm onset, a notable dipolarization is observed and tailward flows commence, characterised by southward magnetic fields in the form of a plasmoid.

    We confirm various observable-parameter variations based on or predicted by the relevant substorm models; however, none of these can explain our results perfectly. Therefore, we propose a catapult (slingshot current-sheet relaxation model, in which an earthward convective flow produced by catapult current-sheet relaxation and a converted duskward flow near the Earth are enhanced through flow braking around 4 min before the substorm onset. These flows induce a ballooning instability or other instabilities, causing the observed current disruption. The formation of the magnetic neutral line is a natural consequence of the present model, because the relaxation of a highly stretched

  20. 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.

  1. Solar and Interplanetary Causes of Extremely Intense Substorms During Superstorms

    Science.gov (United States)

    Tsurutani, Bruce; Hajra, Rajkumar; Echer, Ezequiel; Gjerloev, Jesper

    2016-04-01

    We have begun a study of particularly intense substorms that occur during superstorms. We will relate the solar cycle dependences of events, whether they are externally or internally triggered, and their relationship to other factors such as magnetospheric preconditioning. If time permits, we will explore the details of the events and whether they are similar to regular (Akasofu, 1964) substorms or not. These intense substorms are an important feature of space weather since they may be responsible for power outages.

  2. On storm weakening during substorm expansion phase

    Directory of Open Access Journals (Sweden)

    G. L. Siscoe

    Full Text Available Iyemori and Rao recently presented evidence that the strength of a magnetic storm, as measured by -Dst, weakens, or its rate of growth slows, during the substorm expansion phase. Yet the expansion phase is known to inject energetic particles into the ring current, which should strengthen the storm. We propose to reconcile these apparently contradictory results by combining the virial theorem and a principle of energy partitioning between energy storage elements in a system with dissipation. As applied to the unloading description of the substorm expansion phase, the virial theorem states that -Dst is proportional to the sum of the total magnetic energy and twice the total kinetic energy in the magnetosphere including the tail. Thus if expansion phase involves converting magnetic energy stored in the tail into kinetic energy stored in the ring current, a drop in -Dst during expansion phase requires that less than half the drop in magnetic energy goes into the ring current, the rest going into the ionosphere. Indeed Weiss et al., have estimated that the energy dissipated in the ionosphere during expansion phase is twice that injected into the ring current. This conclusion is also consistent with the mentioned energy partitioning principle, which requires that more energy be dissipated than transferred between storage elements. While Iyemori and Rao's observations seem to contradict the hypothesis that storms consist at least in part of a sum of substorms, this mode of description might nonetheless be preserved by including the substorm's growth-phase contribution. Then the change in storm strength measured from before the growth phase to after the expansion phase is positive, even though the expansion phase alone makes a negative contribution.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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...

  9. 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.

  10. 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...

  11. A Double-Disruption Substorm Model - The Growth Phase

    Science.gov (United States)

    Sofko, G. J.; McWilliams, K. A.; Hussey, G. C.

    2014-12-01

    When the IMF turns from Bz- to Bz+, dayside merging forms open lobe field lines at low latitudes. These lobe lines are populated with shocked solar wind and dayside magnetospheric plasma from the reconnection inflow. As those lobe flux tubes pass tailward over the polar caps, they are also populated with outflow from the north and south polar cap ionospheres. As the lobe lines move tailward, they acquire a convex curvature that blocks the westward-flowing cross-tail current (XTJ). This constitutes the first stage of XTJ disruption, and it begins less than 10 min after the frontside merging.The disrupted XTJ closes dawn-to-dusk in the transition plasmasheet (TPS), where it produces a downward FAC to the ionosphere. This causes the proton arc, which is seen for the period from about 10 - 80 min after frontside merging begins at time t=0. The lobe lines eventually reconnect well downtail at about t=30 minutes. The middle section that closes the lobe lines has concave curvature and is called the Neutral Sheet (NSh). The resulting stretched field lines thus have a central NSh which separates the two convex-curvature regions to the north and south, regions which are called the Disruption Zones (DZs); the overall combination of the NDZ, NSh and SDZ is called the Stretched Plasmasheet (SPS). As the SPS continues to grow and the stretched lines are pulled earthward to relieve the magnetic tension, the filling of the NSh occurs both from the DTNL with the higher energy magnetospheric particle population on the lobe lines, but eventually also at about 25 earth radii when the polar cap ionospheric outflow (PCO) component finally reaches the NSh. A NSh FAC system forms, from which electrons flow down to the auroral ionosphere to create the pre-onset arc, starting at about t=65 min. At the same time, the Lyons-Speiser mechanism is initiated in the inner NSh, causing the PCO ions to become trapped and accelerated in the inner NSh region. Eventually, when the SPS grows earthward

  12. 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.

  13. Spatial scale of the substorm onset region determined from multi-point satellite and ground-based observations

    Science.gov (United States)

    Nakamura, Rumi; Baker, D. N.; Belian, Richard D.; Yamamoto, T.

    1992-01-01

    The temporal and spatial scale of the onset of two substorm events is investigated using high resolution energetic particle and magnetic field data at synchronous orbit plus auroral and magnetic field data simultaneously taken from the ground based instrumentation. During both intervals the major expansion onset had precursor localized expansions without significant negative bay enhancement ('pseudobreakups'). Typical magnetospheric onset signatures such as tail current diversion, dipolarization, and injection were observed associated with some of the pseudobreakups. The major expansion, on the other hand, consisted of a number of rather localized injections and expansions, each of which had times scales of 5 to approximately 10 minutes, a comparable time scale to that of pseudobreakups. The number of occurrences, as well as the scale size of the magnetospheric source region, would constitute the major difference between pseudobreakup and the global expansion onset.

  14. Longitudinal development of a substorm brightening arc

    Directory of Open Access Journals (Sweden)

    K. Shiokawa

    2009-05-01

    Full Text Available We present simultaneous THEMIS-ground observations of longitudinal (eastward extension of a substorm initial-brightening arc at Gillam (magnetic latitude: 65.6° at 08:13 UT on 10 January 2008. The speed of the eastward arc extension was ~2.7 km/s. The extension took place very close to the footprints of the longitudinally separated THEMIS E and D satellites at ~12 RE. The THEMIS satellites observed field dipolarization, weak earthward flow, and pressure increase, which propagated eastward from E to D at a speed of ~50 km/s. The THEMIS A satellite, located at 1.6 RE earthward of THEMIS E, observed fluctuating magnetic field during and after the dipolarization. The THEMIS E/D observations suggest that the longitudinal extension of the brightening arc at substorm onset is caused by earthward flow braking processes which produce field dipolarization and pressure increase propagating in longitude in the near-earth plasma sheet.

  15. 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

  16. Understanding Substorms in the Magnetotail: Early Development and Recent Progress

    Institute of Scientific and Technical Information of China (English)

    A.Nishida

    2011-01-01

    This is a concise review of physics of the substorm in the magnetotail.It consists of two parts.The first part summarizes historical developments in the early days of the space age (1960-1975) when the basic concepts such as magnetotail and reconnection were established and the leading model of the substorm was introduced.The second part is an overview of the research conducted in recent years (1995-2010) when very significant advances have been achieved in understanding the substorm physics by virtue of several major satellites missions that addressed the magnetotail physics intensively.

  17. SAPS onset timing during substorms and the westward traveling surge

    Science.gov (United States)

    Mishin, Evgeny, V.

    2016-07-01

    We present multispacecraft observations in the magnetosphere and conjugate ionosphere of the onset time of subauroral polarization streams (SAPS) and tens of keV ring current injections on the duskside in three individual substorms. This is probably the first unequivocal determination of the substorm SAPS onset timing. The time lag between the SAPS and substorm onsets is much shorter than the gradient-curvature drift time of ˜10 keV ions in the plasmasphere. It seemingly depends on the propagation time of substorm-injected plasma from the dipolarization onset region to the plasmasphere, as well as on the SAPS position. These observations suggest that fast onset SAPS and ring current injections are causally related to the two-loop system of the westward traveling surge.

  18. 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....

  19. 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.

  20. 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.

  1. 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.

  2. The "Alfvénic surge" at substorm onset/expansion and the formation of "Inverted Vs": Cluster and IMAGE observations

    Science.gov (United States)

    Hull, A. J.; Chaston, C. C.; Frey, H. U.; Fillingim, M. O.; Goldstein, M. L.; Bonnell, J. W.; Mozer, F. S.

    2016-05-01

    From multipoint, in situ observations and imaging, we reveal the injection-powered, Alfvénic nature of auroral acceleration during onset and expansion of a substorm. It is shown how Alfvénic variations over time dissipate to form large-scale, inverted-V structures characteristic of quasistatic aurora. This characterization is made possible through the fortuitous occurrence of a substorm onset and expansion phase on field lines traversed by Cluster in the high-altitude acceleration region. Substorm onset was preceded by the occurrence of multiple poleward boundary intensifications (PBIs) and subsequent development/progression of a streamer toward the growth phase arc indicating that this is of the PBI-/streamer-triggered class of substorms. Onset on Cluster is marked by the injection of hot, dense magnetospheric plasma in a region tied to one of the preexisting PBI current systems. This was accompanied by a surge of Alfvénic activity and enhanced inverted-V acceleration, as the PBI current system intensified and striated to dispersive scale Alfvén waves. The growth of Alfvén wave activity was significant (up to a factor of 300 increase in magnetic field power spectral density at frequencies 20 mHz ≲f≲ few hertz) and coincided with moderate growth (factor 3-5) in the background PBI current. This sequence is indicative of a cascade process whereby small-scale/dispersive Alfvén waves are generated from large-scale Alfvén waves or current destabilization. It also demonstrates that the initial PBIs and their subsequent evolution are an intrinsic part of the global auroral substorm response to injection and accompanying wave energy input from the magnetotail. Alfvénic activity persisted poleward of the PBI currents composing a broad Alfvén wave-dominated region extending to the polar cap edge. These waves have transverse scales ranging from a few tens of kilometers to below the ion gyroradius and are associated with large electric fields (up to 200 mV/m) and

  3. What effect do substorms have on the content of the radiation belts?

    OpenAIRE

    C. Forsyth; Rae, I.; Murphy, K.; Freeman, M.; Huang, C.-L.; Spence, H; Boyd, A. (Adele); Coxon, J; Jackman, C.; Kalmoni, N.; Watt, C.

    2016-01-01

    Abstract Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave‐particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belt...

  4. Flow braking and the substorm current wedge

    Science.gov (United States)

    Birn, J.; Hesse, M.; Haerendel, G.; Baumjohann, W.; Shiokawa, K.

    1999-09-01

    Recent models of magnetotail activity have associated the braking of earthward flow with dipolarization and the reduction and diversion of cross-tail current, that is, the signatures of the substorm current wedge. Estimates of the magnitude of the diverted current by Haerendel [1992] and Shiokawa et al. [1997, 1998] tend to be lower than results from computer simulations of magnetotail reconnection and tail collapse [Birn and Hesse, 1996], despite similar underlying models. An analysis of the differences between these estimates on the basis of the simulations gives a more refined picture of the diversion of perpendicular into parallel currents. The inertial currents considered by Haerendel [1992] and Shiokawa et al. [1997] contribute to the initial current reduction and diversion, but the dominant and more permanent contribution stems from the pressure gradient terms, which change in connection with the field collapse and distortion. The major effect results from pressure gradients in the z direction, rather than from the azimuthal gradients [Shiokawa et al., 1998], combined with changes in By and Bx. The reduction of the current density near the equatorial plane is associated with a reduction of the curvature drift which overcompensates changes of the magnetization current and of the gradient B drift current. In contrast to the inertial current effects, the pressure gradient effects persist even after the burst of earthward flow ends.

  5. Solar wind and substorm excitation of the wavy current sheet

    Science.gov (United States)

    Forsyth, C.; Lester, M.; Fear, R. C.; Lucek, E.; Dandouras, I.; Fazakerley, A. N.; Singer, H.; Yeoman, T. K.

    2009-06-01

    Following a solar wind pressure pulse on 3 August 2001, GOES 8, GOES 10, Cluster and Polar observed dipolarizations of the magnetic field, accompanied by an eastward expansion of the aurora observed by IMAGE, indicating the occurrence of two substorms. Prior to the first substorm, the motion of the plasma sheet with respect to Cluster was in the ZGSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the -YGSM direction. Following the second substorm, the current sheet waves caused multiple current sheet crossings of the Cluster spacecraft, previously studied by Zhang et al. (2002). We further this study to show that the velocity of the current sheet waves was similar to the expansion velocity of the substorm aurora and the expansion of the dipolarization regions in the magnetotail. Furthermore, we compare these results with the current sheet wave models of Golovchanskaya and Maltsev (2005) and Erkaev et al. (2008). We find that the Erkaev et al. (2008) model gives the best fit to the observations.

  6. Solar wind and substorm excitation of the wavy current sheet

    Directory of Open Access Journals (Sweden)

    C. Forsyth

    2009-06-01

    Full Text Available Following a solar wind pressure pulse on 3 August 2001, GOES 8, GOES 10, Cluster and Polar observed dipolarizations of the magnetic field, accompanied by an eastward expansion of the aurora observed by IMAGE, indicating the occurrence of two substorms. Prior to the first substorm, the motion of the plasma sheet with respect to Cluster was in the ZGSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the −YGSM direction. Following the second substorm, the current sheet waves caused multiple current sheet crossings of the Cluster spacecraft, previously studied by Zhang et al. (2002. We further this study to show that the velocity of the current sheet waves was similar to the expansion velocity of the substorm aurora and the expansion of the dipolarization regions in the magnetotail. Furthermore, we compare these results with the current sheet wave models of Golovchanskaya and Maltsev (2005 and Erkaev et al. (2008. We find that the Erkaev et al. (2008 model gives the best fit to the observations.

  7. DR-current intensity variations during substorm development

    Science.gov (United States)

    Zaitseva, S. A.; Drobinina, T. A.; Pudovkin, M. I.

    2003-04-01

    According to the concept dominated by the last time, the intensification of the DR-current takes place during the polar substorm development. In the recent papers Iyemori and Rao claim that geomagnetic storms and substorms are independent processes, and SYM-index (essentially the same as Dst-index) tends to decay after the onset of substorms. In this paper we tried to clear up the cause of this contradiction by studying the connection of ring current development with polar substorms basing on the new data: ASY-, SYM-indices describing asymmetric and symmetric parts of DR-current correspondingly and AL-index as a measure of polar disturbances. It is shown that the hourly-mean SYM- and ASY-indices correlate with AL-index (r=0.63 and 0.69 correspondingly), and the connection between these values becomes worse for strong storms. Besides, at the substorm expansive phase onset, the energy can put mainly to the asymmetric part rather than into symmetric part of DR-current. Empirical Q-index based on solar wind parameters describes the energy input into DR-current; Q correlates rather well with SYM, ASY and AL-indices. Thus the intensifications of polar disturbances and DR-current take place simultaneously and have the same source.At the same time, the proportion in which the solar wind energy is distributed between the DR-current, polar ionosphere and magnetotail depends on the Dst variation phase.

  8. 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.

  9. Strong induction effects during the substorm on 27 August 2001

    Science.gov (United States)

    Mishin, V. V.; Mishin, V. M.; Lunyushkin, S. B.; Pu, Z.; Wang, C.

    2015-10-01

    We report on strong induction effects notably contributing to the cross polar cap potential drop and the energy balance during the growth and active phases of the substorm on 27 August 2001. The inductance of the magnetosphere is found to be crucial for the energy balance and electrical features of the magnetosphere in the course of the substorm. The inductive response to the switching on and off of the solar wind-magnetosphere generator exceeds the effect of the interplanetary magnetic field (IMF) variation. The induction effects are most apparent during the substorm expansion onset when the rapid growth of the ionospheric conductivity is accompanied by the fast release of the magnetic energy stored in the magnetotail during the growth phase. Using the magnetogram inversion technique, we estimated the magnetospheric inductance and effective ionospheric conductivity during the loading and unloading phases.

  10. Pc5 waves generated by substorm injection: a case study

    Directory of Open Access Journals (Sweden)

    N. A. Zolotukhina

    2008-07-01

    Full Text Available We analyzed the spectral-polarized characteristics of Pc5 ULF waves observed on 17 September 2000 after the 03:20:25 UT substorm onset with the satellites GOES 8 and 10 located east and west of the onset location. In the course of the event, the wave polarization changed from mixed (between toroidal and poloidal to poloidal, and then to mixed again. The hodogram of magnetic field oscillations rotated counterclockwise at GOES 8, and clockwise at GOES 10. It is suggested that the satellites detected the waves generated by the substorm injected clouds of the charged particles drifting in the magnetosphere in the opposite azimuthal directions: GOES 8 (located east of the substorm onset detected the wave generated by an electron cloud, and GOES 10 (west of the onset detected the wave generated by a positive ion cloud. This interpretation is confirmed by the energetic particles data recorded by LANL satellites.

  11. 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

  12. Cross-tail current evolution during substorm dipolarization

    Directory of Open Access Journals (Sweden)

    A. T. Y. Lui

    2013-06-01

    Full Text Available We examine evolution of the cross-tail current during substorm current disruption/dipolarization using observations from two satellites in the near-Earth magnetotail at the downtail distances of 8–9 RE. By choosing times when these two satellites are separated, mainly in the north–south distance in the tail current sheet, precise determination of current density in the layer embedded between these satellites can be obtained with Ampère's law. Two such events are examined and several common features are found. The current densities in the layer embedded by the two satellites were reduced by ~ 40–70% during substorm dipolarization. The changes in current densities have the fast kinetic timescale, i.e., in seconds, implying a kinetic process for current disruption/dipolarization. The estimated power within the current layer was mainly dissipative in the dawn–dusk direction and mainly dynamo in the Sun–tail direction that is needed to drive the north–south substorm current system in the ionosphere. Remote sensing of the energization site with the ion sounding technique shows that the energization site was initially earthward of the satellite and moved down the tail at later times. Breakdown of the frozen-in condition occurred intermittently during the disturbance interval. These features provide important clues to the substorm onset process.

  13. 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...

  14. 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...

  15. Theories and Simulations in Substorm Research: A Review

    Institute of Scientific and Technical Information of China (English)

    R. A. WOLF

    2011-01-01

    Both theory and simulation have played important roles in defining and illuminating the key mechanisms involved in substorms. Basic theories of magnetic reconnection and of interchange and ballooning instabilities were developed more than 50 years ago, and these plasma physical concepts have been central in discussions of substorm physics. A vast amount of research on reconnection, including both theoretical and computational studies, has helped provide a picture of how reconnection operates in the collisionless environment of the magnetosphere. Still, however, we do not fully understand how key microscale processes and large-scale dynamics work together to determine the location and rate of reconnection. While in the last twenty years, it has become clear that interchange processes are important for transporting plasma through the plasma sheet in the form of bursty bulk flows and substorm expansions, we still have not reached the point where simulations are able to realistically and defensibly represent all of the important aspects of the phenomenon. More than two decades ago it was suggested that the ballooning instability, the basic theory for which dates from the 1950s, may play an important role in substorms. Now the majority of experts agree that regions of the plasma sheet are often linearly unstable to ideal-MHD ballooning. However, it is also clear that kinetic effects introduce important modifications to the MHD stability criterion. It is still uncertain whether ballooning plays a leading role in substorms or has just a minor part. Among the different types of simulations that have been applied to the substorm problem, global MHD codes are unique in that, in a sense, they represent the entire global substorm phenomenon, including coupling to the solar wind and ionosphere, and the important mechanisms of reconnection, interchange, and ballooning. However, they have not yet progressed to the point where they can accurately represent the whole phenomenon

  16. 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...

  17. 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.

  18. 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.

  19. 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

  20. 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.

  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. 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.

  3. From the Solar Wind to the Magnetospheric Substorm

    Institute of Scientific and Technical Information of China (English)

    E.A. Ponomarev; P.A. Sedykh; O.V. Mager

    2005-01-01

    This paper gives a brief outline of the progression from the first substorm model developed in Ref.[4] and [8] based on Kennel's ideas[3], to the present views about the mechanism by which solar wind kinetic energy is converted to electromagnetic energy at the Bow Shock and by which this energy is transferred to the magnetosphere in the form of current; about the transformation of the energy of this current to gas kinetic energy of convecting plasma tubes, and, finally, the back transformation of gas kinetic energy to electromagnetic energy in secondary magnetospheric MHD generators. The questions of the formation of the magnetospheric convection system, the nature of substorm break-up, and of the matching of currents in the magnetosphere-ionosphere system are discussed.

  4. Excitation of Whistler-Mode (Chorus) Emissions during Terrestrial Substorms

    Institute of Scientific and Technical Information of China (English)

    XIAO Fu-Liang; ZHAO Hua; HE Hui-Yong

    2005-01-01

    @@ The enhanced growth rate of whistler mode waves has been evaluated during an injection event associated with an isolated terrestrial substorm that occurred at 23:00 UT, on January 21, 1991. The electron phase space density observed by an LEPA instrument on the board of the CRRES spacecraft is modelled by using a bi-loss-cone distribution function (composed of a high anisotropic component and a quasi-isotropic component). During the injection event, the path integrated gain may increase by a factor of 5 over a frequency range near a few tenths of the electron gyrofrequency, which is consistent with the enhancement observed in the CRRES plasma wave experiment (PWE) emissions. Scattering of electrons by the enhanced whistler mode waves causes the pitch angle distribution of resonant electrons to a quasi isotropic (flat-top) distribution during the terrestrial substorm injection event.

  5. Quantitative Simulation of a Magnetospheric Substorm. 2. Comparison with Observations,

    Science.gov (United States)

    1980-01-23

    we overestimated the polar-boundary potential drop; consequently the p) asma -sheet ions were injected deeper into the magnetosphere than was the case...Magnetospheric Substorms and Related Plasma Processes, Los Alamos, New Mexico , October 1978 and to be published in Astrophysics and Space Science Library...and Related Plasma Processes, Los Alamos, New Mexico , October 1978, published in Astrophysics and Space Science Library Series,p.14 3, Yasuhara, F., and

  6. Two satellite study of substorm expansion near geosynchronous orbit

    Directory of Open Access Journals (Sweden)

    Ø. Holter

    2004-12-01

    Full Text Available During several time intervals in 1979–1980 the satellites GEOS-2 and SCATHA were situated relatively close on the nightside of the Earth at geosynchronous distances. Several substorm events were identified during these periods. The event considered in this paper was recorded on 22 May 1979, when the satellites were separated by less than 30min in local time around 21:00 LT. The observed 45 to 60 s delay of magnetic signatures observed at the two s/c indicates a westward expansion of ~7.7°/min. At the two s/c, the magnetic signatures are, in particular for the azimuthal magnetic field components, quite different. At GEOS-2, being close to the magnetic equator, the dominant feature is a dipolarization with a weak field-aligned current signature corresponding to a symmetric current which cancels at the equator. On SCATHA, however, being close to the current sheet boundary, the azimuthal magnetic field indicates a strong field-aligned Birkeland current structure. On both s/c the first indication of an approaching substorm was an increase in the high energy ion flux followed by a reduction in the flux intensity of energetic electrons and a further tailward stretching of the magnetic field, starting ~2min before the onset of the magnetic field dipolarization. The tailward stretching, the observed variations of the magnetic field components, and the subsequent dipolarization are interpreted in terms of an azimuthally tilted field-aligned current system passing the s/c on the tailward side from east to west. The westward expansion and dipolarization observed at the two s/c are consistent with the propagation of a Rayleigh-Taylor type instability. The increased radial ion flux corresponds to the ExB-drift due to the substorm associated electric field.

    Key words. Magnetospheric physics (storms and substorms; plasma waves and instabilities; current systems

  7. Conditions for substorm onset by the fast reconnection mechanism

    Directory of Open Access Journals (Sweden)

    M. Ugai

    2008-12-01

    Full Text Available The fast reconnection mechanism, involving slow shocks and Alfvénic fast plasma jets, is most responsible for the explosive conversion of magnetic energy associated with geomagnetic substorms and solar flares. In this paper, the spontaneous fast reconnection model is applied to well-known phenomena of substorms. When the east-west width of the tail current sheet becomes 3–4 times larger than its north-south thickness, the fast reconnection mechanism can fully be established, which may lead to substorm onset. The resulting Alfvénic jet can exactly explain, both qualitatively and quantitatively, the in-situ satellite observations of the traveling compression regions (TCRs associated with large-scale plasmoids propagating down the tail. Also, the earthward fast reconnection jet causes drastic magnetic field dipolarization, so that the sheet current ahead of the magnetic loop of closed field lines suddenly turns its direction toward the loop footpoint and a large-scale current wedge is formed according to the growth of field-aligned currents. It is demonstrated that an MHD generator arises ahead of the magnetic loop and drives the current wedge to distinctly enhance the current density in a pair of thin layers of the loop footpoint, giving rise to drastic heating in the form of two ribbons.

  8. Modelling substorm chorus events in terms of dispersive azimuthal drift

    Directory of Open Access Journals (Sweden)

    A. B. Collier

    2004-12-01

    Full Text Available The Substorm Chorus Event (SCE is a radio phenomenon observed on the ground after the onset of the substorm expansion phase. It consists of a band of VLF chorus with rising upper and lower cutoff frequencies. These emissions are thought to result from Doppler-shifted cyclotron resonance between whistler mode waves and energetic electrons which drift into a ground station's field of view from an injection site around midnight. The increasing frequency of the emission envelope has been attributed to the combined effects of energy dispersion due to gradient and curvature drifts, and the modification of resonance conditions and variation of the half-gyrofrequency cutoff resulting from the radial component of the ExB drift.

    A model is presented which accounts for the observed features of the SCE in terms of the growth rate of whistler mode waves due to anisotropy in the electron distribution. This model provides an explanation for the increasing frequency of the SCE lower cutoff, as well as reproducing the general frequency-time signature of the event. In addition, the results place some restrictions on the injected particle source distribution which might lead to a SCE.

    Key words. Space plasma physics (Wave-particle interaction – Magnetospheric physics (Plasma waves and instabilities; Storms and substorms

  9. 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.

  10. Jumps of the solar wind direction and the substorm probability

    Science.gov (United States)

    Kubyshkina, Daria; Kubyshkina, Marina; Semenov, Vladimir

    2015-04-01

    Magnetospheric substorm commonly supposed to consist of two stages, loading and unloading. During the first stage the magnetic energy is stored in the magnetotail, which leads to increasing of the magnetic field intensity in the lobes and electric currents in the plasma sheet. The next uloading stage usually related to the reconnection process, which releases accumulated magnetic energy and produces the bursty bulk flows (BBFs) in the magnetotail. Such a scheme has been confirmed from both experimental and theoretical points of view. The weakest point of this scheme is the physical conditions which are necessary for the onset of the reconnection, but although the huge number of investigations was made to this end. Among them substorm triggers such as pressure pulses, turning of the interplanetary magnetic field (IMF) to the north direction and so on. We would like to emphasize the role of the bent current sheets first proposed by Kivelson and Hughes in 1990. The idea is that in the asymmetric configurations gradients and current density growth, so these conditions are supposed to be favorable for the reconnection. Then the minimal stress of the system can lead to the substorm onset. In the presented study we have analyzed the possibility of the current sheet asymmetry to be the trigger in theory and in observations (by statistical analysis of substorm occurrences). The bent of the current sheet can be produced by different sources. The most evident of them are the dipole tilt angle variations and the changes of the solar wind direction. The first source, tilt variations, are slow, so in the current study we at first analyzed the fast changes of the solar wind. The experimental analysis includes the investigation of the number of the events against dipole tilt angle and the solar wind direction, which both produce the distortion and inclination of the dipole current sheet. Theoretical investigation of this issue is based on the analysis of the quasi

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. The high latitude convection response to an interval of substorm activity

    Directory of Open Access Journals (Sweden)

    T. K. Yeoman

    Full Text Available On 17 March 1991, five clear substorm onsets/intensifications took place within a three hour interval. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were available, in addition to data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation. This interval of substorm activity has been interpreted as being in support of a near-Earth current disruption model of substorm onset. In the present study the ionospheric convection response, observed some four hours to the west in MLT by the Halley HF radar in Antarctica, is related to the growth, expansion and recovery phases of two of the substorm onsets/expansions observed in the Northern Hemisphere. Bursts of ionospheric flow and motion of the convection reversal boundary (CRB are observed at Halley in response to the substorm activity and changes in the IMF. The delay between the substorm expansion phase onset and the response in the CRB location is dependent on the local time separation from, and latitude of, the initial substorm onset region. These results are interpreted in terms of a synthesis of the very near-Earth current disruption model and the near-Earth neutral line model of substorm onset.

  17. Investigation of isolated substorms: Generation conditions and characteristics of different phases

    Science.gov (United States)

    Vorobjev, V. G.; Yagodkina, O. I.; Zverev, V. L.

    2016-11-01

    Characteristics of isolated substorms selected by variations in the 1-min values of the AL index are analyzed. The substorms were divided into several types with respect to the behavior of the Bz component of the interplanetary magnetic field (IMF) during the expansion phase. The probability of observations of substorms associated with the northward turn of the Bz component of IMF was 19%, while the substorms taking place at Bz 30 min) period of the southward IMF and a following sharp turn of the Bz component of IMF before the north was detected. The data suggest that a northward IMF turn is neither a necessary nor sufficient condition for generating substorms. It has been shown for substorms of the both types that the average duration of the southward IMF to moment T 0 and the average intensity of the magnetic perturbation in the maximum are approximately the same and amount to 80 min and-650 nT, respectively. However, for substorms at Bz loading-unloading processes in the magnetosphere in the periods of magnetospheric substorms were investigated with different functions that determine the efficiency of the energy transfer from the solar wind to the magnetosphere. It has been shown that the highest correlation coefficient ( r = 0.84) is observed when the function suggested by Newell et al. (2007) is used. It has been detected that a simple function VB S yields a high correlation coefficient ( r = 0.75).

  18. What effect do substorms have on the content of the radiation belts?

    Science.gov (United States)

    Forsyth, C.; Rae, I. J.; Murphy, K. R.; Freeman, M. P.; Huang, C.-L.; Spence, H. E.; Boyd, A. J.; Coxon, J. C.; Jackman, C. M.; Kalmoni, N. M. E.; Watt, C. E. J.

    2016-07-01

    Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV "seed" population into the inner magnetosphere which is subsequently energized through wave-particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1-3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM-H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels.

  19. What effect do substorms have on the content of the radiation belts?

    Science.gov (United States)

    Forsyth, C; Rae, I J; Murphy, K R; Freeman, M P; Huang, C-L; Spence, H E; Boyd, A J; Coxon, J C; Jackman, C M; Kalmoni, N M E; Watt, C E J

    2016-07-01

    Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV "seed" population into the inner magnetosphere which is subsequently energized through wave-particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1-3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM-H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels.

  20. 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.

  1. 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.

  2. Prompt enhancement of the Earth's outer radiation belt due to substorm electron injections

    Science.gov (United States)

    Tang, C. L.; Zhang, J.-C.; Reeves, G. D.; Su, Z. P.; Baker, D. N.; Spence, H. E.; Funsten, H. O.; Blake, J. B.; Wygant, J. R.

    2016-12-01

    We present multipoint simultaneous observations of the near-Earth magnetotail and outer radiation belt during the substorm electron injection event on 16 August 2013. Time History of Events and Macroscale Interactions during Substorms A in the near-Earth magnetotail observed flux-enhanced electrons of 300 keV during the magnetic field dipolarization. Geosynchronous orbit satellites also observed the intensive electron injections. Located in the outer radiation belt, RBSP-A observed enhancements of MeV electrons accompanied by substorm dipolarization. The phase space density (PSD) of MeV electrons at L* 5.4 increased by 1 order of magnitude in 1 h, resulting in a local PSD peak of MeV electrons, which was caused by the direct effect of substorm injections. Enhanced MeV electrons in the heart of the outer radiation belt were also detected within 2 h, which may be associated with intensive substorm electron injections and subsequent local acceleration by chorus waves. Multipoint observations have shown that substorm electron injections not only can be the external source of MeV electrons at the outer edge of the outer radiation belt (L* 5.4) but also can provide the intensive seed populations in the outer radiation belt. These initial higher-energy electrons from injection can reach relativistic energy much faster. The observations also provide evidence that enhanced substorm electron injections can explain rapid enhancements of MeV electrons in the outer radiation belt.

  3. Substorm-related thermospheric density and wind disturbances derived from CHAMP observations

    Directory of Open Access Journals (Sweden)

    P. Ritter

    2010-06-01

    Full Text Available The input of energy and momentum from the magnetosphere is most efficiently coupled into the high latitude ionosphere-thermosphere. The phenomenon we are focusing on here is the magnetospheric substorm. This paper presents substorm related observations of the thermosphere derived from the CHAMP satellite. With its sensitive accelerometer the satellite can measure the air density and zonal winds. Based on a large number of substorm events the average high and low latitude thermospheric response to substorm onsets was deduced. During magnetic substorms the thermospheric density is enhanced first at high latitudes. Then the disturbance travels at an average speed of 650 m/s to lower latitudes, and 3–4 h later the bulge reaches the equator on the night side. Under the influence of the Coriolis force the travelling atmospheric disturbance (TAD is deflected westward. In accordance with present-day atmospheric models the disturbance zonal wind velocities during substorms are close to zero near the equator before midnight and attain moderate westward velocities after midnight. In general, the wind system is only weakly perturbed (Δvy<20 m/s by substorms.

  4. A comparison of substorms occurring during magnetic storms with those occurring during quiet times

    Science.gov (United States)

    McPherron, R. L.; Hsu, T.-S.

    2002-09-01

    It has been suggested that there may be a fundamental difference between substorms that occur during magnetic storms and those that occur at other times. [1996] presented evidence that there is no obvious change in lobe field in "quiet time" substorms but that "storm time" substorms exhibit the classic pattern of storage and release of lobe field energy. This result led them to speculate that the former are caused by current sheet disruption, while the latter are caused by reconnection of lobe flux. In this paper we examine their hypothesis with a much larger data set using definitions of the two types of substorms similar to theirs, as well as additional more restrictive definitions of these classes of events. Our results show that the only differences between the various classes are the absolute value of the lobe field and the size of the changes. When the data are normalized to unit field amplitude, we find that the percent change during storm time and non-storm time substorms is nearly the same. The above conclusions are demonstrated with superposed epoch analysis of lobe field (Bt and Bz) for four classes of substorms: active times (Dst -25 nT), and quiet time substorms (no evidence of storm in Dst). Epoch zero for the analysis was taken as the main substorm onset (Pi2 onset closest to sharp break in AL index). Our results suggest that there is no qualitative distinction between the various classes of substorms, and so they are all likely to be caused by the same mechanism.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. The physics of plasma injection events. [during magnetospheric substorms

    Science.gov (United States)

    Kivelson, M. G.; Kaye, S. M.; Southwood, D. J.

    1980-01-01

    In this paper, plasma injection is defined as an increase of particle flux in a detector of finite bandwidth. Injection can result from dynamic processes or from spacecraft penetration of a quasi-static spatial structure produced by a steady magnetospheric convection pattern. ATS-5 particle spectrograms are found to provide examples of plasma injection events of both sorts. Dynamic injection occurs both with and without local magnetic signatures. For events not associated with clear local magnetic signatures, convection theory with a steady or a time-varying uniform electric field can account for the energy dispersion of injected particles with energy less than 50 keV. The paper concludes with a discussion of the way in which the convection boundaries are related to the substorm injection boundary of Mauk and McIlwain. Several alternative expressions for the local time and K(p) dependence of the injection boundary are given.

  13. Numerical modelling of the thermosphere-ionosphere coupling during substorm

    Science.gov (United States)

    Korenkov, Yu. N.; Bessarab, F. S.; Klimenko, V. V.; Surotkin, V. A.; Smertin, V. M.

    The numerical calculation results of the thermospheric parameters ([O]/[N_2] ratio and Tn) and critical frequencies of F2-region of ionosphere, foF2, in the global scale for the recovery phase of the substorm are presented. The calculations were executed with the use of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) was constructed in the Kaliningrad Observatory of the IZMIRAN and modified in the Polar Geophysical Institute. The influences of the global distribution of Joule dissipation on the neutral atmosphere and ionosphere parameters are discussed. It is emphasised that the Joule dissipation in the neutral atmosphere is a main cause of the negative disturbance in the F2 region of the ionosphere.

  14. Phenomenological and Theoretical Studies on Magnetic Indicators of Substorm Activity.

    Science.gov (United States)

    1980-03-21

    kkurr,,nts, Planet. Space Scl., 23, 1355-1368, 1975. 96VOL. 84. NO. AllI JOURNAL OF GEOPHYSICAL RESEARCH NOVEMBER 1. 1979 On the Orientation of the...latitude electric fields I laiend u Ao paaes csea rer th s edc xvtmde lue W e- Geop.vs. Res.. 82. 1115-1125i 1977. pcndupo paametrs n te coduciviy moel...deviation. From uqsenhoven et al. (1978). 131 VOL 83. NO AI0 JOURNAL OF GEOPHYSICAL RESEARCH OCTOBER J. 1978 Characteristics of the Equatorward Auroral

  15. A Catapult (Slingshot) Current Sheet Relaxation Model for Substorm Triggering

    Science.gov (United States)

    Machida, S.; Miyashita, Y.; Ieda, A.

    2010-12-01

    Based on the results of our superposed epoch analysis of Geotail data, we have proposed a catapult (slingshot) current sheet relaxation model in which earthward flows are produced in the central plasma sheet (CPS) due to the catapult (slingshot) current sheet relaxation, together with the rapid enhancement of Poynting flux toward the CPS in the lobe around X ~ -15 Re about 4 min before the substrom onset. These earthward flows are characterized by plasma pressure decrease and large amplitude magnetic field fluctuations. When these flows reach X ~ 12Re in the magnetotail, they give significant disturbances to the inner magnetosphere to initiate some instability such as a ballooning instability or other instabilities, and the substorm starts in the inner magnetosphere. The occurrence of the magnetic reconnection is a natural consequence of the initial convective earthward flows, because the relaxation of a highly stretched catapult current sheet produces a very thin current at its tailward edge being surrounded by intense magnetic fields which were formerly the off-equatorial lobe magnetic fields. Recently, Nishimura et al. [2010] reported that the substorm onset begins when faint poleward discrete arcs collide with equatorward quiet arcs. The region of earthward convective flows correlatively moves earthward prior to the onset. Thus, this region of the earthward convective flows seems to correspond to the faint poleward discrete arcs. Interestingly, our statistical analysis shows that the earthward convective flows are not produced by the magnetic reconnection, but they are attributed to the dominance of the earthward JxB force over the tailward pressure associated with the progress of the plasma sheet thinning.

  16. 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.

  17. 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.

  18. 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....

  19. 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....

  20. 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).

  1. 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

  2. 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.

  3. Dying Flow Bursts as Generators of the Substorm Current Wedge

    Science.gov (United States)

    Haerendel, Gerhard

    2016-07-01

    Many theories or conjectures exist on the driver of the substorm current wedge, e.g. rerouting of the tail current, current disruption, flow braking, vortex formation, and current sheet collapse. Magnitude, spatial scale, and temporal development of the related magnetic perturbations suggest that the generator is related to the interaction of the flow bursts with the dipolar magnetosphere after onset of reconnection in the near-Earth tail. The question remains whether it is the flow energy that feeds the wedge current or the internal energy of the arriving plasma. In this presentation I argue for the latter. The current generation is attributed to the force exerted by the dipolarized magnetic field of the flow bursts on the preceding layer of high-beta plasma after flow braking. The generator current is the grad-B current at the outer boundary of the compressed high-beta plasma layers. It needs the sequential arrival of several flow bursts to account for duration and magnitude of the ionospheric closure current.

  4. Response of plasmaspheric configuration to substorms revealed by Chang’e 3

    Science.gov (United States)

    He, Han; Shen, Chao; Wang, Huaning; Zhang, Xiaoxin; Chen, Bo; Yan, Jun; Zou, Yongliao; Jorgensen, Anders M.; He, Fei; Yan, Yan; Zhu, Xiaoshuai; Huang, Ya; Xu, Ronglan

    2016-08-01

    The Moon-based Extreme Ultraviolet Camera (EUVC) of the Chang’e 3 mission provides a global and instantaneous meridian view (side view) of the Earth’s plasmasphere. The plasmasphere is one inner component of the whole magnetosphere, and the configuration of the plasmasphere is sensitive to magnetospheric activity (storms and substorms). However, the response of the plasmaspheric configuration to substorms is only partially understood, and the EUVC observations provide a good opportunity to investigate this issue. By reconstructing the global plasmaspheric configuration based on the EUVC images observed during 20–22 April 2014, we show that in the observing period, the plasmasphere had three bulges which were located at different geomagnetic longitudes. The inferred midnight transit times of the three bulges, using the rotation rate of the Earth, coincide with the expansion phase of three substorms, which implies a causal relationship between the substorms and the formation of the three bulges on the plasmasphere. Instead of leading to plasmaspheric erosion as geomagnetic storms do, substorms initiated on the nightside of the Earth cause local inflation of the plasmasphere in the midnight region.

  5. 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

  6. Spring-fall asymmetry of substorm strength, geomagnetic activity and solar wind: Implications for semiannual variation and solar hemispheric asymmetry

    Science.gov (United States)

    Marsula, K.; Tanskanen, E.; Love, J.J.

    2011-01-01

    We study the seasonal variation of substorms, geomagnetic activity and their solar wind drivers in 1993–2008. The number of substorms and substorm mean duration depict an annual variation with maxima in Winter and Summer, respectively, reflecting the annual change of the local ionosphere. In contradiction, substorm mean amplitude, substorm total efficiency and global geomagnetic activity show a dominant annual variation, with equinoctial maxima alternating between Spring in solar cycle 22 and Fall in cycle 23. The largest annual variations were found in 1994 and 2003, in the declining phase of the two cycles when high-speed streams dominate the solar wind. A similar, large annual variation is found in the solar wind driver of substorms and geomagnetic activity, which implies that the annual variation of substorm strength, substorm efficiency and geomagnetic activity is not due to ionospheric conditions but to a hemispherically asymmetric distribution of solar wind which varies from one cycle to another. Our results imply that the overall semiannual variation in global geomagnetic activity has been seriously overestimated, and is largely an artifact of the dominant annual variation with maxima alternating between Spring and Fall. The results also suggest an intimate connection between the asymmetry of solar magnetic fields and some of the largest geomagnetic disturbances, offering interesting new pathways for forecasting disturbances with a longer lead time to the future.

  7. 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.

  8. 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.

  9. 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...

  10. 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.

  11. Charged Particle Energization and Transport in the Magnetotail during Substorms

    Science.gov (United States)

    Pan, Qingjiang

    This dissertation addresses the problem of energization of particles (both electrons and ions) to tens and hundreds of keV and the associated transport process in the magnetotail during substorms. Particles energized in the magnetotail are further accelerated to even higher energies (hundreds of keV to MeV) in the radiation belts, causing space weather hazards to human activities in space and on ground. We develop an analytical model to quantitatively estimate flux changes caused by betatron and Fermi acceleration when particles are transported along narrow high-speed flow channels from the magnetotail to the inner magnetosphere. The model shows that energetic particle flux can be significantly enhanced by a modest compression of the magnetic field and/or shrinking of the distance between the magnetic mirror points. We use coordinated spacecraft measurements, global magnetohydrodynamic (MHD) simulations driven by measured upstream solar wind conditions, and large-scale kinetic (LSK) simulations to quantify electron local acceleration in the near-Earth reconnection region and nonlocal acceleration during plasma earthward transport. Compared to the analytical model, application of the LSK simulations is much less restrictive because trajectories of millions of test particles are calculated in the realistically determined global MHD fields and the results are statistical. The simulation results validated by the observations show that electrons following a power law distribution at high energies are generated earthward of the reconnection site, and that the majority of the energetic electrons observed in the inner magnetosphere are caused by adiabatic acceleration in association with magnetic dipolarizations and fast flows during earthward transport. We extend the global MHD+LSK simulations to examine ion energization and compare it with electron energization. The simulations demonstrate that ions in the magnetotail are first nonadiabatically accelerated in the weak

  12. Streaming energetic electrons in earth's magnetotail - Evidence for substorm-associated magnetic reconnection

    Science.gov (United States)

    Bieber, J. W.; Stone, E. C.

    1980-01-01

    This letter reports the results of a systematic study of streaming greater than 200 keV electrons observed in the magnetotail with the Caltech Electron/Isotope Spectrometers aboard IMP-7 and IMP-8. A clear statistical association of streaming events with southward magnetic fields, often of steep inclination, and with substorms as evidenced by the AE index is demonstrated. These results support the interpretation that streaming energetic electrons are indicative of substorm-associated magnetic reconnection in the near-earth plasma sheet.

  13. Simulation of the interchange instability in a magnetospheric substorm site

    Directory of Open Access Journals (Sweden)

    O. V. Mingalev

    2006-07-01

    Full Text Available We perform modeling of the interchange instability driven by longitudinal pressure asymmetry in the region of the pressure buildup that forms in the inner magnetosphere at the substorm growth phase. The simulation refers to the dawnward side of the Harang discontinuity and times after Bz IMF turning northward. The solution for the equilibrium state indicates tailward flows associated with vortices, which is in agreement with a previous finding of Ashour-Abdalla et al. (1999, 2002. We show that in the regions of equilibrium field-aligned currents (FACs, small initial perturbations in pVγ (p is the isotropic plasma pressure, V is the unit magnetic flux tube volume, γ=5/3 the adiabatic exponent, set up as ripples inclined to azimuth, grow in time. For the background FAC of ~10-6 A/m2, the linear growth rate of the instability is ~6 min. Starting from the 12th min of evolution, the perturbations exhibit nonlinear deformations, develop undulations and front steepening. An interesting peculiarity in the distribution of the associated small-scale FACs is that they become asymmetric with time. Specifically, the downward currents are more localised, reaching densities up to 15×10-6 A/m2 at the nonlinear stage. The upward FACs are more dispersed. When large enough, these currents are likely to produce the aurora. We also run our simulation for the initial perturbations of large transverse scales in order to demonstrate that the interchange instability can be responsible for pressure and cross-tail current spatial variations of great extent.

  14. 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.

  15. Simultaneous observations of the near-earth and distant geomagnetic tail during a substorm by ISEE-1, ISEE-3 and geostationary spacecraft

    Science.gov (United States)

    Richardson, I. G.; Scholer, M.; Tsurutani, B. T.; Daly, P. W.; Baker, D. N.

    1987-01-01

    The structure of the geomagnetic tail during a substorm is investigated by combining plasma, magnetic field, and energetic particle data from the ISEE-3 spacecraft in the deep tail with similar near-earth observations from ISEE-1 and geostationary spacecraft. The observations can be interpreted in terms of the neutral-line model of substorms and indicate the formation of a closed-loop field region (plasmoid) following substorm onset, which is ejected down the tail. The plasmoid is observed to have a double-loop field strucure. This may be the result of a second substorm onset occurring about 25 min after the first, producing a further near-earth neutral line and closed field loop. During the substorm recovery phase, the substorm neutral line moves tailward to beyond 130 earth radii from earth by some 3 h after substorm onset.

  16. 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.

  17. 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

  18. Global MHD simulation and analysis of Feb. 22, 2009 THEMIS substorm event

    Science.gov (United States)

    Zhu, P.; Raeder, J.; Sakaguchi, K.; Shiokawa, K.; Hegna, C.

    2009-12-01

    Rayleigh-Taylor (RT)-like finger patterns have been observed in the diffuse aurora image at the beginning of recovery phase during recent Feb. 22, 2009 THEMIS substorm event [Sagaguchi and Shiokawa, 2009]. In this work, efforts are undertaken to identify the plasma processes in the magnetotail region that may be associated with or contribute to the formation of the RT-like aurora structure. Using the solar wind data from ACE satellite observation for the substorm event as an input at day-side, OpenGGCM simulations are used to reconstruct a sequence of global magnetospheric configurations around the Feb. 22, 2009 substorm onset. We benchmark the simulation with the THEMIS satellite data and compare the electron precipitation flux pattern in ionosphere region with the aurora images from all-sky ground observations. The ballooning stability criterion and growth rates of the near-Earth plasma sheet region are evaluated prior to the substorm onset time. The question we are addressing is if the RT-like aurora image pattern could be a footprint or projection of the ballooning-interchange processes in the plasma sheet. Research supported by NSF Grant No. ATM-0902360.

  19. 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

  20. Search for an onset mechanism that operates for both CMEs and substorms

    Directory of Open Access Journals (Sweden)

    G. L. Siscoe

    2009-08-01

    Full Text Available Substorms and coronal mass ejections have been cited as the most accessible examples of the explosive energy conversion phenomenon that seems to characterize one of the behavior modes of cosmic plasmas. This paper addresses the question of whether these two examples – substorms and CMEs – support or otherwise the idea that explosive energy conversion is the result of a single process operating in different places and under different conditions. As a candidate mechanism that might be common to both substorms and CMEs we use the Forbes catastrophe model for CMEs because before testing it appears to have the potential, suitably modified, to operate also for substorms. The essence of the FCM is a sudden onset of an imbalance of the forces acting on an incipient CME. The imbalance of forces causes the CME to start to rise. Beneath the rising CME conditions develop that favor the onset of magnetic reconnection which then releases the CME and assists its expulsion. Thus the signature of the FCM is a temporally ordered sequence in which there is first the appearance of force imbalance which leads to upward (or outward motion of the CME which leads to magnetic reconnection under it which expedites rapid expulsion. We look for the FCM signature in the output of two global magnetospheric MHD simulations that produce substorm-like events. We find the ordered sequence of events as stated but with a significant difference: there is no plasmoid prior to the onset of rapid reconnection, that is, there is no counterpart to the incipient CME on which an imbalance of forces acts to initiate the action in the FCM. If this result – that rapid tailward motion precedes the rapid reconnection of substorm expansion – is ultimately verified by other studies, it suggests that a description of the cause of substorm expansion should identify the cause of the preceding rapid tailward motion, since this leads necessarily to rapid reconnection, whatever the

  1. 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.

  2. The radial evolution of earthward BBFs during substorm

    Institute of Scientific and Technical Information of China (English)

    REME; H; DANDOURAS; I; LUCEK; E; DUNLOP; M

    2010-01-01

    We here study the occurrence rate,probability function of velocity and duration of earthward bursty bulk flows(BBFs) in the Inner Plasma Sheet(IPS,β>0.5) using the data of Cluster in 2001 and 2002.The occurrence rate of earthward BBFs increases with distance from the Earth up to ?19 RE,which is in agreement with the previous observations of the radial evolution of BBFs.About 54% of earthward BBFs in expansion phase have a velocity larger than 600 km/s,whereas only 38% of earthward BBFs in growth and recovery phases have a velocity larger than 600 km/s.The average velocity of earthward BBFs in expansion phase is 732 km/s,larger than those in growth phase(631 km/s) and recovery phase(617 km/s).The durations of earthward BBFs decrease with the decrease of downtail distance from Earth due to the braking of earthward BBFs.The duration of earthward BBFs in expansion phase is larger than that in growth and recovery phases.The average durations in growth,expansion,and recovery phases are respectively 49.3,71.5,and 47.6 s.Therefore,the ratios of transports of energy of earthward BBFs in growth,expansion,and recovery phases can be estimated to be 0.51:1:0.47.Thus,the earthward BBFs in the expansion phase have the largest capability of the transport of energy and can produce the largest braking effects,such as inertial currents and auroral activities.

  3. Irregular HF radio propagation on a subauroral path during magnetospheric substorms

    Directory of Open Access Journals (Sweden)

    D. V. Blagoveshchensky

    2006-08-01

    Full Text Available The impact of the main ionospheric trough, sporadic structures, gradients and inhomogeneities of the subpolar ionosphere during substorms on the signal amplitude, azimuthal angles of arrival, and propagation modes for the radio path Ottawa (Canada-St. Petersburg (Russia was considered. This subauroral path with the length of about 6600 km has approximately an east-west orientation. The main goals are to carry out numerical modeling of radio propagation for the path and to compare the model calculations with experimental results. Wave absorption and effects of focusing and divergence of rays were taken into consideration in the radio wave modeling process. The following basic results were obtained: The signal amplitude increases by 20–30 dB 1–1.5 h before the substorm expansion phase onset. At the same time the signal azimuth deviates towards north of the great circle arc for the propagation path. Compared with quiet periods there are effects due to irregularities and gradients in the area of the polar edge of the main ionospheric trough on the passing signals. Propagation mechanisms also change during substorms. The growth of signal amplitude before the substorm can be physically explained by both a decrease of the F2-layer ionization and a growth of the F2-layer height that leads to a decrease of the signal field divergence and to a drop of the collision frequency. Ionospheric gradients are also important. This increase of signal level prior to a substorm could be used for forecasting of space weather disturbed conditions.

  4. 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.

  5. 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.

  6. 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.

  7. 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...

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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...

  15. 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.

  16. 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.

  17. A statistical study of magnetic field magnitude changes during substorms in the near earth tail

    Science.gov (United States)

    Lopez, R. E.; Lui, A. T. Y.; Mcentire, R. W.; Potemra, T. A.; Krimigis, S. M.

    1990-01-01

    Using AMPTE/CCE data taken in 1985 and 1986 when the CCE apogee (8.8 earth radii) was within 4.5 hours of midnight, 167 injection events in the near-earth magnetotail have been cataloged. These events are exactly or nearly dispersionless on a 72-sec time scale from 25 keV to 285 keV. The changes in the field magnitude are found to be consistent with the expected effects of the diversion/disruption of the cross-tail current during a substorm, and the latitudinal position of the current sheet is highly variable within the orbit of CCE. The local time variation of the magnetic-field changes implies that the substorm current wedge is composed of longitudinally broad Birkeland currents.

  18. Impulse Travel Time from the Magnetotail to the Aurora Region during substorm: OpenGGCM Simulation

    Science.gov (United States)

    Ferdousi, Banafsheh; Raeder, Jimmy

    2016-07-01

    The onset of substorms is an unsolved problem in Space Physics although there are many models explaining the substorm process. Studying the processes that occur during first 2 minutes of substorm depends critically on the correct timing between different signals in the plasma sheet and the ionosphere. This has been difficult to accomplish with data alone, since signals are sometimes ambiguous, or they have not been observed in the right locations. To investigate signal propagation paths and signal travel times, we use Magnetohydrodynamic global simulations of the Earth magnetosphere: OpenGGCM. The waves are created at different locations in the magnetotail by perturbing plasma pressure in the plasma sheet. Thus, we can study wave path in the magnetotail and determine its travel time to the ionosphere. Contrary to previous studies, we find that wave travel reach the ionosphere from the midtail around 60 seconds. We also find that waves travel faster through the lobes, and the Tamao path is not generally the preferred path for waves originating in the plasma sheet. Furthermore, we find that the impulses that are generated closer to earth lead to dispersed ionosphere signatures, whereas the impulses originated in midtail region lead to more localized signatures.

  19. The mid-high latitude whistler mode chorus waves observed around substorm onsets

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Using the data of LFEW/TC-2, we studied the dawn side chorus around substorm onsets during a strong geomagnetic storm in November 2004. During this storm, LFEW/TC-2 observed 14 dawnside chorus events. Nine of them were associated with substorms and occurred within 40 min around the substorm onsets. The fre-quencies of waves have a very good correlation with the half equatorial electron cyclotron frequencies. Chorus can be excited in the region near magnetic equato-rial plane and then propagate to the mid and high latitudes. When the wave fre-quencies reach the local lower hybrid frequencies, chorus can be reflected due to the lower hybrid resonance. The time delay between the chorus and its echo is about 28 min. Previous observations show that the chorus can propagate at most to the magnetic latitudes of 40°. LFEW/ TC-2 found for the first time that the chorus in space could propagate to the magnetic latitude of 70°. Since most of the previous chorus observations are made close to the magnetic equatorial plane, our results are important for the studies of excitation and propagation of whistler mode wave, and relevant relativistic electron acceleration in the magnetosphere.

  20. Global Simulation of Proton Precipitation Due to Field Line Curvature During Substorms

    Science.gov (United States)

    Gilson, M. L.; Raeder, J.; Donovan, E.; Ge, Y. S.; Kepko, L.

    2012-01-01

    The low latitude boundary of the proton aurora (known as the Isotropy Boundary or IB) marks an important boundary between empty and full downgoing loss cones. There is significant evidence that the IB maps to a region in the magnetosphere where the ion gyroradius becomes comparable to the local field line curvature. However, the location of the IB in the magnetosphere remains in question. In this paper, we show simulated proton precipitation derived from the Field Line Curvature (FLC) model of proton scattering and a global magnetohydrodynamic simulation during two substorms. The simulated proton precipitation drifts equatorward during the growth phase, intensifies at onset and reproduces the azimuthal splitting published in previous studies. In the simulation, the pre-onset IB maps to 7-8 RE for the substorms presented and the azimuthal splitting is caused by the development of the substorm current wedge. The simulation also demonstrates that the central plasma sheet temperature can significantly influence when and where the azimuthal splitting takes place.

  1. The mid-high latitude whistler mode chorus waves observed around substorm onsets

    Institute of Scientific and Technical Information of China (English)

    YANG JunYing; CAO JinBin; YAN ChunXiao; LI LiuYuan; MA YuDuan

    2008-01-01

    Using the data of LFEW/TC-2, we studied the dawn side chorus around substorm onsets during a strong geomagnetic storm in November 2004. During this storm, LFEW/TC-2 observed 14 dawnside chorus events. Nine of them were associated with substorms and occurred within 40 min around the substorm onsets. The fre-quencies of waves have a very good correlation with the half equatorial electron cyclotron frequencies. Chorus can be excited in the region near magnetic equato-rial plane and then propagate to the mid and high latitudes. When the wave fre-quencies reach the local lower hybrid frequencies, chorus can be reflected due to the lower hybrid resonance. The time delay between the chorus and its echo is about 28 min. Previous observations show that the chorus can propagate at most to the magnetic latitudes of 40°. LFEW/TC-2 found for the first time that the chorus in space could propagate to the magnetic latitude of 70°. Since most of the previous chorus observatlons are made close to the magnetic equatorial plane, our results are Important for the studies of excitation and propagation of whistler mode wave, and relevant relativistic electron acceleration in the magnetosphere.

  2. 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.

  3. 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.

  4. 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

  5. pTC-1 observation of ion high-speed flow reversal in the near-Earth plasma sheet during substorm

    Institute of Scientific and Technical Information of China (English)

    H.; RME; I.; DANDOURAS; C.; M.; CARR

    2008-01-01

    Based on measurements of FGM and HIA on board TC-1 at its apogee on Septem-ber 14, 2004, we analyzed the ion high-speed flows in the near-Earth plasma sheet observed during the substorm expansion phase. Strong tailward high-speed flows (Vx ~ -350 km/s) were first seen at about X ~ -13.2 RE in near-Earth magnetotail, one minute later the flows reversed from tailward to earthward. The reversal process occurred quickly after the substorm expansion onset. The near-Earth magnetotail plasma sheet was one of key regions for substorm onset. Our analysis showed that the ion flow reversal from tailward to earthward was likely to be in close relation with the substorm expansion initiation and might play an important role in trigger-ing the substorm expansion onset.

  6. Wp index: A new substorm index derived from high-resolution geomagnetic field data at low latitude

    DEFF Research Database (Denmark)

    Nose, M.; Iyemori, T.; Wang, L.

    2012-01-01

    Geomagnetic field data with high time resolution (typically 1 s) have recently become more commonly acquired by ground stations. Such high time resolution data enable identifying Pi2 pulsations which have periods of 40-150 s and irregular (damped) waveforms. It is well-known that pulsations...... of this type are clearly observed at mid-and low-latitude ground stations on the nightside at substorm onset. Therefore, with 1-s data from multiple stations distributed in longitude around the Earth's circumference, substorm onset can be regularly monitored. In the present study we propose a new substorm...... index, the Wp index (Wave and planetary), which reflects Pi2 wave power at low-latitude, using geomagnetic field data from 11 ground stations. We compare the Wp index with the AE and ASY indices as well as the electron flux and magnetic field data at geosynchronous altitudes for 11 March 2010. We find...

  7. A Simulation Study of the Thermosphere Mass Density Response to Substorms Using GITM Model

    Science.gov (United States)

    Liu, X.; Ridley, A. J.

    2014-12-01

    The temporal and spatial variations of the thermosphere mass density during a variety of idealized substorms were investigated using the Global Ionosphere Thermosphere Model (GITM) simulation and Challenging Minisatellite Payload (CHAMP) satellite. From the GITM simulation, the maximum mass density perturbation of an idealized substorm with a peak variation of Hemispheric Power (HP) Index of 50 GW and interplanetary magnetic field (IMF) Bz of -2 nT was ~14% about 50 min after the substorm onset in the nightside sector of the aurora zone. About 110 min after onset, a negative mass density perturbation (~-5%) occurred in the night sector, which was consistent with the mass density measurement of the CHAMP satellite. Further investigation suggests that a large scale in situ gravity wave was generated in the aurora zone and propagated to the mid and low latitudes. Simulations with IMF Bz changes, with HP being constant and HP changing and IMF Bz being constant were run to investigate any nonlinearities in the combined response. The mass density perturbation due the IMF Bz variation peaks in the dusk sector and the density perturbation due to HP input peaks in the nightside sector. The non-linear of the mass density response to different energy input is less than 6%. The thermospheric mass density at higher altitudes is more sensitive to the Joule heating energy input. The change in hemisphere power adds electron density to lower altitudes, so the heating due to the HP change is at lower altitudes than the heating due to the IMF Bz change. This causes the density change due to the HP change to be larger than the density change due to the IMF change.

  8. The Origin of the Near-Earth Plasma Population During a Substorm on November 24, 1996

    Science.gov (United States)

    Ashour-Abdalla, M.; El-Alaoui, M.; Peroomian, V.; Walker, R. J.; Raeder, J.; Frank, L. A.; Paterson, W. R.

    1999-01-01

    We investigate the origins and the transport of ions observed in the near-Earth plasma sheet during the growth and expansion phases of a magnetospheric substorm that occurred on November 24, 1996. Ions observed at Geotail were traced backward in time in time-dependent magnetic and electric fields to determine their origins and the acceleration mechanisms responsible for their energization. Results from this investigation indicate that, during the growth phase of the substorm, most of the ions reaching Geotail had origins in the low latitude boundary layer (LLBL) and had already entered the magnetosphere when the growth phase began. Late in the growth phase and in the expansion phase a higher proportion of the ions reaching Geotail had their origin in the plasma mantle. Indeed, during the expansion phase more than 90% of the ions seen by Geotail were from the mantle. The ions were accelerated enroute to the spacecraft; however, most of the ions' energy gain was achieved by non-adiabatic acceleration while crossing the equatorial current sheet just prior to their detection by Geotail. In general, the plasma mantle from both southern and northern hemispheres supplied non-adiabatic ions to Geotail, whereas the LLBL supplied mostly adiabatic ions to the distributions measured by the spacecraft. Distribution functions computed at the ion sources indicate that ionospheric ions reaching Geotail during the expansion phase were significantly heated. Plasma mantle source distributions indicated the presence of a high-latitude reconnection region that allowed ion entry into the magnetosphere when the IMF was northward. These ions reached Geotail during the expansion phase. Ions from the traditional plasma mantle had access to the spacecraft throughout the substorm.

  9. Integrated Observations of ICME - Driven Substorm - Storm Evolution on 7 August 1998: Traditional and Non-Traditional Aspects.

    Science.gov (United States)

    Farrugia, C. J.; Sandholt, P. E.; Torbert, R. B.

    2015-12-01

    The aim of this study is to obtain an integrated view of substorm-storm evolution in relation to well-defined interplanetary (IP) conditions, and to identify traditional and non-traditional aspects of the DP1 and DP2 current systems during substorm activity. Specifically, we report a case study of substorm/storm evolution driven by an ICME from ground observations around the oval in relation to geoeffective IP parameters (Kan-Lee electric field, E-KL, and dynamic pressure, Pdyn), geomagnetic indices (AL, SYM-H and PCN) and satellite observations (from DMSP F13 and F14, Geotail, and GOES spacecraft). A sudden enhancement of E-KL at a southward turning of the IMF led to an initial transient phase (PCN-enhancement) followed by a persistent stage of solar wind-magnetosphere-ionosphere coupling. The persistent phase terminated abruptly at a steep E-KL reduction when the ICME magnetic field turned north after a 3-hour-long interval of enhanced E-KL. The persistent phase consisted of (i) a 45-min-long substorm growth phase (DP2 current) followed by (ii) a classical substorm onset (DP1 current) in the 0100 - 0300 MLT sector, (ii) a 30-min-long expansion phase, maximizing in the same sector, and (iii) a phase lasting for 1.5 hr of 10-15 min-long DP1 events in the 2100 - 2300 and 0400 - 0600 MLT sectors. In the morning sector the expansion phase was characterized by Ps6 pulsations and omega bands. The SYM-H evolution reached the level of a major storm after a 2.5-hour-long interval of E-KL ˜5 mV/m and elevated Pdyn in the substorm expansion phase. Magetosphere - Ionosphere (M - I) coupling during a localized electrojet event at 0500 MLT in the late stage of the substorm expansion is studied by ground - satellite conjunction data (Iceland - Geotail). The DP1 and DP2 components of geomagnetic activity are discussed in relation to M - I current systems and substorm current wedge morphology.

  10. Rapid enhancement of energetic oxygen ions in the inner magnetosphere during substorms

    Science.gov (United States)

    Nakayama, Y.; Ebihara, Y.; Tanaka, T.

    2014-12-01

    Satellite observations show that energetic (>100 keV) O+ ions are rapidly increased in the inner magnetosphere during substorms. The ultimate source of O+ ions is the Earth's ionosphere, so that O+ ions must be accelerated from ~eV to 100s keV somewhere in the magnetosphere. A fundamental question still arise regarding why O+ ions are accelerated and transported to the inner magnetosphere. We simulated substorms under two different solar wind conditions by using the global MHD simulation developed by Tanaka et al. (2010, JGR). The solar wind speed is set to be 372 km/s for Case I, and 500 km/s for Case II. In both cases, the MHD simulation result shows that the dawn to dusk electric field is enhanced in the night side tail region at >7 Re just after the substorm onset. In particular, the electric field in the inner region (~7 Re) is highly enhanced by the tension force because of relatively strong magnetic field together with curved field lines. The strongest electric field takes place near the region where the plasma pressure is high. We performed test particle simulation under the electric and magnetic fields for Cases I and II. O+ ions are released from two planes located at ±2 Re in the Z direction in the tail region. O+ ions released at the two planes represent outflowing stream of O+ ions escaping from the Earth. The distribution function at the planes is assumed to be drifting Kappa distribution with temperature of 10 eV, the density of 105 m-3, and the parallel velocity given by the MHD simulation. In total, around a billion of particles are traced. Each test particle carries the real number of particles in accordance with the Liouville theorem. After tracing particles, we reconstructed 6-dimensional phase space density of O+ ions. We obtained the following results. (1) Just after substorm onset, the differential flux of O+ ions is almost simultaneously enhanced in the region where the electric field is strong. (2) The kinetic energy increases rapidly to

  11. Investigation of a CTS solar cell test patch under simulated geomagnetic substorm charging conditions

    Science.gov (United States)

    Bogus, K. P.

    1977-01-01

    The CTS solar array technology experiment which consists of a solar cell test patch on the Kapton-substrate solar array and the appertaining electronics unit has been operating in geostationary orbit for nearly 1 year without any malfunction although it is expected to be strongly influenced by charging effects on the array surface. The results of a post-launch test program show that the experiment would not survive a discharge due to electrostatic charging in the test patch area. In a simulated substorm, environment discharges were obtained only below a temperature threshold of about 30 C. With solar illumination, this threshold is reduced below 0 C.

  12. 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.

  13. 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.

  14. Improved electron and ion temperatures and application to the Nov-24-12 substorm

    Science.gov (United States)

    Zhu, J.; Ridley, A. J.

    2014-12-01

    Improved energy equations have been implemented for both electrons and ions in the Global Ionosphere Thermosphere Model (GITM). The sources of the electron temperature include heating due to photoionization, elastic collisions with ions, elastic and inelastic collisions with neutrals, as well as energy fluxes from the magnetosphere. The sources of the ion temperature include elastic collisions with electrons, and energy exchanges with neutrals accounting for Joule heating and due to temperature difference. The model was constructed using a semi-implicit method on the thermal conduction and all of the temperature-dependent source terms [Huba and Joyce, 2000]. The Nov-24-2012 substorm is investigated using the improved model. The Joule heating and its effect on the ion and neutral temperatures in high-latitudes between the improved and basic models are compared. It is also shown that a decrease in the electron temperature exists in the region of the aurora oval with high electron densities. The partitioning of energy between different source terms and loss terms is investigated throughout the substorm and as a function of location.

  15. 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.

  16. 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.

  17. A statistical study of magnetic dipolarization for sawtooth events and isolated substorms at geosynchronous orbit with GOES data

    Directory of Open Access Journals (Sweden)

    X. Cai

    2006-12-01

    Full Text Available We investigate whether the dipolarization process during sawtooth events is global or not through an examination of the local time distribution of the magnetic tilt angle (i.e. the angle between the B vector and the equatorial plane in dipole VDH coordinates at geostationary orbit. From the statistical analysis of 207 individual teeth and 212 isolated substorms, we find that individual teeth follow a dipolarization pattern similar to that observed for isolated substorms. The dipolarization for individual teeth initiates in the sector between 22:00 magnetic local time (MLT and 00:00 MLT. Then the dipolarization expands both eastward and westward. However, relative to isolated substorms, we find that the nightside magnetosphere is much more stretched prior to the onset, and the change of the tilt angle during the dipolarization process is much larger during individual teeth. The magnetic dipolarization is seen over a wider local time sector during individual teeth than during isolated substorms. However, the magnetic dipolarization is rarely observed near local noon during individual teeth. This suggests that the magnetic dipolarization process during individual teeth is still confined primarily to the nightside.

  18. 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

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Midtail plasma flows and the relationship to near-Earth substorm activity: A case study

    Science.gov (United States)

    Lopez, R. E.; Goodrich, C. C.; Reeves, G. D.; Belian, R. D.; Taktakishvili, A.

    1994-12-01

    Recent simulations of magnetotail reconnection have pointed to a link between plasma flows, dipolarization, and the substorm current wedge. In particular, Hesse and Birn (1991) have proposed that earthward jetting of plasma from the reconnection region transports flux into the near-Earth region. At the inner edge of the plasma sheet this flux piles up, producing a dipolarization of the magnetic field. The vorticity produced by the east-west deflection of the flow at the inner edge of the plasma sheet gives rise to field-aligned currents that have region 1 polarity. Thus in this scenario the earthward flow from the reconnection region produces the dipolarization and the current wedge in a self-consistent fashion. In this study we examine observations made on April 8, 1985 by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (IRM), the geosynchronous satellites 1979-053, 1983-019, and 1984-037, and Syowa station, as well as AE. This event is unique because IRM was located near the neutral sheet in the midnight sector for an extended period of time. Ground data show that there was ongoing activity in the IRM local time sector for several hours, beginning at 1800 UT and reaching a crescendo at 2300 UT. This activity was also accompanied by energetic particle variations, including injections, at geosynchronous orbit in the nighttime sector. Significantly, there were no fast flows at the neutral sheet until the great intensification of activity at 2300 UT. At that time, IRM recorded fast earthward flow simultaneous with a dipolarization of the magnetic field. We conclude that while the aforementioned scenario for the creation of the current wedge encounters serious problems explaining the earlier activity, the observations at 2300 UT are consistent with the scenario of Hesse and Birn (1991). On that basis it is argued that the physics of substorms is not exclusively rooted in the development of a global tearing mode. Processes at the inner edge of

  7. The observations of high energy electrons and associated waves by DSP satellites during substorm

    Energy Technology Data Exchange (ETDEWEB)

    Cao Jinbin [Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, 100080 (China); Yang Junying; Yan Chunxiao [Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, 100080 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Li Liyuan [Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, 100080 (China)

    2007-04-15

    Double Star Program (DSP) is a CNSA-ESA cooperation mission. DSP consists of two satellites: Equatorial satellite (TC-1) and Polar satellite (TC-2). This paper presents important observations of long duration loss of high energetic electrons and relevant waves in the recovery phase of substorm, that are made by LFEW and HEED of the polar satellite of DSP (TC-2). The HEED of TC-2 observed a loss event of high energetic electrons which lasted about 4 minute. At the same time, the LFEW of TC-2 observed a wave burst. The wave burst began 1 minute earlier than the loss event of energetic electrons. The frequency of waves ranges form 600 Hz to over 10 kHz. The analyses of wave characteristics indicate that the wave was whistler-mode. Thus it is very possible that the loss of high energy electrons was caused by wave activities through wave-particle interactions.

  8. Streaming reversal of energetic particles in the magnetotail during a substorm

    Science.gov (United States)

    Lui, A. T. Y.; Williams, D. J.; Eastman, T. E.; Frank, L. A.; Akasofu, S.-I.

    1984-01-01

    A case of reversal in the streaming anisotropy of energetic ions and in the plasma flow observed from the IMP 8 spacecraft during a substorm on February 8, 1978 is studied in detail using measurements of energetic particles, plasma, and magnetic field. Four new features emerge when high time resolution data are examined in detail. The times of streaming reversal of energetic particles in different energy ranges do not coincide with the time of plasma flow reversal. Qualitatively different velocity distributions are observed in earthward and tailward plasma flows during the observed flow reversal intervals. Strong tailward streaming of energetic particles can be detected during northward magnetic field environments and, conversely, earthward streaming in southward field environments. During the period of tailward streaming of energetic particles, earthward streaming fluxes are occasionally detected.

  9. Substorm effects on the plasma sheet on composition on March 22, 1979 (CDAW 6)

    Energy Technology Data Exchange (ETDEWEB)

    Lennartsson, W.; Sharp, R.D.; Zwickl, R.D.

    1985-02-01

    Data from the Plasma Composition Experiment on ISSE 1, covering the energy range 0.1--16 keV/e, show that a dramatic change took place in the plasma sheet ion composition in conjunction with the magnetic substorm activity on March 22, 1979. Beginning about 1124 UT the ion population at the ISEE 1 location changed from what appeared to be predominantly ions from the solar wind to a mixture of comparable numbers of solar wind and terrestrial ions. ISEE 1 was inbound in the predawn sector during this time, and the plasma composition experiment provided data from Rapprox. =21 R/sub E/ and LTapprox. =0130, down to Rapprox. =3 R/sub E/ and LTapprox. =0530. Prior to the substorm activity about 90--95% of the ion density was due to H/sup +/ and He/sup + +/ ions, which appeared to be mostly of solar wind origin. The H/sup +/ and He/sup + +/ components, each approximated by a Maxwell-Boltzmann distribution, had a temperature ratio T(He/sup + +/)/T(H/sup +/)approx. =4 and a density ratio n(He/sup + +/)/n(H/sup +/)approx. =1.5--3%. Both values are consistent with measurements made concurrently in the solar wind by the plasma experiment on ISSE 3. The remaining 5--10% of the density was due mainly to O/sup +/ and He/sup +/ ions of ionospheric origin. All four ion populations had broad energy spectra with mean energies of several keV/e.

  10. 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.

  11. 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.

  12. 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).

  13. 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.

  14. 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.

  15. 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.

  16. A substorm-associated enhancement in the XUV radiation measuring channel observed by ESP/EVE/SDO

    Science.gov (United States)

    Yan, Yan; Wang, Hua-Ning; Shen, Chao; Du, Zhan-Le

    2016-06-01

    Comparing the ESP/EVE/SDO flux data of 2011 Feb 6, with the counterparts of XRS/GOES and SEM/SOHO, we find that there is an enhancement that is not apparent in the two latter datasets. The enhancement, possibly regarded as a flare at first glimpse, nevertheless, does not involve an energy-release from the Sun. Based on the enhancement, we combine data from SXI/GOES 15 into a synthesized analysis, and concluded that it arises from a particle-associated enhancement in the channel that measures XUV radiation. Paradoxically, it seems to be somewhat of a particle-avalanching process. Prior to the event, a moderate geomagnetic storm took place. Subsequently, while the event is proceeding, a geomagnetic substorm is simultaneously observed. Therefore, the particles, though unidentified, are probably energetic electrons induced by substorm injection.

  17. 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.

  18. Simulating the Thinning Magnetotail Current Sheet During a Substorm Growth Phase with the Rice Convection Model-Equilibrium

    Science.gov (United States)

    Lemon, C. L.; Crabtree, C. E.; Chen, M.; Guild, T. B.

    2015-12-01

    Modeling the progression of the magnetotail configuration during a substorm growth phase is challenging because the current sheet becomes very thin, and is difficult to resolve while keeping the problem computationally tractable. Magnetohydrodynamics (MHD) models have dealt with this problem in various ways, and many claim to be driven by physical rather than numerical considerations. The Rice Convection Model-Equilibrium (RCM-E) is not an MHD model, and has advantages and disadvantages compared to MHD. The notable advantages are the characterization of the full energy distribution of the plasma (including the associated gradient/curvature drift), as well as its generally more comprehensive treatment of the electrodynamics of magnetosphere-ionosphere coupling. The disadvantages include the bounce-averaging of plasma drift, which limits the domain to closed field lines, and the assumption of slow flow relative to the Alfvén speed. The RCM-E has been used in the past to model a substorm growth phase, but its assumptions do not allow it to properly treat the onset mechanism or the formation of x-lines. It can simulate the approach to onset, but is limited by its ability to resolve the thinning current sheet. In this presentation, we present advances in the technique used to calculate the self-consistent magnetic field, which allows us to resolve thinner current sheets than were previously possible. We combine this with a generalized ballooning mode analysis of specific flux tubes in order to assess the stability of the magnetotail to substorm onset.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Magnetotail Current Sheet Thinning and Magnetic Reconnection Dynamics in Global Modeling of Substorms

    Science.gov (United States)

    Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.; DeZeeuw, D. L.; Gombosi, T. I.

    2008-01-01

    Magnetotail current sheet thinning and magnetic reconnection are key elements of magnetospheric substorms. We utilized the global MHD model BATS-R-US with Adaptive Mesh Refinement developed at the University of Michigan to investigate the formation and dynamic evolution of the magnetotail thin current sheet. The BATSRUS adaptive grid structure allows resolving magnetotail regions with increased current density up to ion kinetic scales. We investigated dynamics of magnetotail current sheet thinning in response to southwards IMF turning. Gradual slow current sheet thinning during the early growth phase become exponentially fast during the last few minutes prior to nightside reconnection onset. The later stage of current sheet thinning is accompanied by earthward flows and rapid suppression of normal magnetic field component $B-z$. Current sheet thinning set the stage for near-earth magnetic reconnection. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is non-gyrotropic effects with spatial scales comparable with the particle Larmor radius. One of the major challenges in global MHD modeling of the magnetotail magnetic reconnection is to reproduce fast reconnection rates typically observed in smallscale kinetic simulations. Bursts of fast reconnection cause fast magnetic field reconfiguration typical for magnetospheric substorms. To incorporate nongyritropic effects in diffusion regions we developed an algorithm to search for magnetotail reconnection sites, specifically where the magnetic field components perpendicular to the local current direction approaches zero and form an X-type configuration. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated self-consistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites and spatial scales of the diffusion region are updated

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. Spatial variation of eddy-diffusion coefficients in the turbulent plasma sheet during substorms

    Directory of Open Access Journals (Sweden)

    M. Stepanova

    2009-04-01

    Full Text Available Study of the plasma turbulence in the central plasma sheet was performed using the Interball-Tail satellite data. Fluctuations of the plasma bulk velocity in the plasma sheet were deduced from the measurements taken by the Corall instrument for different levels of geomagnetic activity and different locations inside the plasma sheet. The events that satisfied the following criteria were selected for analysis: number density 0.1–10 cm−3, ion temperature T≥0.3 keV, and average bulk velocity ≤100 km/s. It was found that the plasma sheet flow generally appears to be strongly turbulent, i.e. is dominated by fluctuations that are unpredictable. Corresponding eddy-diffusion coefficients in Y- and Z-direction in the GSM coordinate system were derived using the autocorrelation time and rms velocity. Statistical studies of variation of the eddy-diffusion coefficients with the location inside the plasma sheet showed a significant increase in these coefficients in the tailward direction. During substorms this dependence shows strong increase of eddy-diffusion in the central part of the plasma sheet at the distances of 10–30 Earth's radii. This effect is much stronger for Y-components of the eddy-diffusion coefficient, which could be related to the geometry of the plasma sheet, allowing more room for development of eddies in this direction.

  12. A Mechanism for the Loading-Unloading Substorm Cycle Missing in MHD Global Magnetospheric Simulation Models

    Science.gov (United States)

    Klimas, A. J.; Uritsky, V.; Vassiliadis, D.; Baker, D. N.

    2005-01-01

    Loading and consequent unloading of magnetic flux is an essential element of the substorm cycle in Earth's magnetotail. We are unaware of an available global MHD magnetospheric simulation model that includes a loading- unloading cycle in its behavior. Given the central role that MHD models presently play in the development of our understanding of magnetospheric dynamics, and given the present plans for the central role that these models will play in ongoing space weather prediction programs, it is clear that this failure must be corrected. A 2-dimensional numerical driven current-sheet model has been developed that incorporates an idealized current- driven instability with a resistive MHD system. Under steady loading, the model exhibits a global loading- unloading cycle. The specific mechanism for producing the loading-unloading cycle will be discussed. It will be shown that scale-free avalanching of electromagnetic energy through the model, from loading to unloading, is carried by repetitive bursts of localized reconnection. Each burst leads, somewhat later, to a field configuration that is capable of exciting a reconnection burst again. This process repeats itself in an intermittent manner while the total field energy in the system falls. At the end of an unloading interval, the total field energy is reduced to well below that necessary to initiate the next unloading event and, thus, a loading-unloading cycle results. It will be shown that, in this model, it is the topology of bursty localized reconnection that is responsible for the appearance of the loading-unloading cycle.

  13. Electron dynamics during substorm dipolarization in Mercury's magnetosphere

    Directory of Open Access Journals (Sweden)

    D. C. Delcourt

    2005-11-01

    Full Text Available We examine the nonlinear dynamics of electrons during the expansion phase of substorms at Mercury using test particle simulations. A simple model of magnetic field line dipolarization is designed by rescaling a magnetic field model of the Earth's magnetosphere. The results of the simulations demonstrate that electrons may be subjected to significant energization on the time scale (several seconds of the magnetic field reconfiguration. In a similar manner to ions in the near-Earth's magnetosphere, it is shown that low-energy (up to several tens of eV electrons may not conserve the second adiabatic invariant during dipolarization, which leads to clusters of bouncing particles in the innermost magnetotail. On the other hand, it is found that, because of the stretching of the magnetic field lines, high-energy electrons (several keVs and above do not behave adiabatically and possibly experience meandering (Speiser-type motion around the midplane. We show that dipolarization of the magnetic field lines may be responsible for significant, though transient, (a few seconds precipitation of energetic (several keVs electrons onto the planet's surface. Prominent injections of energetic trapped electrons toward the planet are also obtained as a result of dipolarization. These injections, however, do not exhibit short-lived temporal modulations, as observed by Mariner-10, which thus appear to follow from a different mechanism than a simple convection surge.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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

  1. Role of substorm-associated impulsive electric fields in the ring current development during storms

    Directory of Open Access Journals (Sweden)

    N. Yu. Ganushkina

    2005-02-01

    Full Text Available Particles with different energies produce varying contributions to the total ring current energy density as the storm progresses. Ring current energy densities and total ring current energies were obtained using particle data from the Polar CAMMICE/MICS instrument during several storms observed during the years 1996-1998. Four different energy ranges for particles are considered: total (1-200keV, low (1-20keV, medium (20-80keV and high (80-200keV. Evolution of contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases is followed. To model this evolution we trace protons with arbitrary pitch angles numerically in the drift approximation. Tracing is performed in the large-scale and small-scale stationary and time-dependent magnetic and electric field models. Small-scale time-dependent electric field is given by a Gaussian electric field pulse with an azimuthal field component propagating inward with a velocity dependent on radial distance. We model particle inward motion and energization by a series of electric field pulses representing substorm activations during storm events. We demonstrate that such fluctuating fields in the form of localized electromagnetic pulses can effectively energize the plasma sheet particles to higher energies (>80keV and transport them inward to closed drift shells. The contribution from these high energy particles dominates the total ring current energy during storm recovery phase. We analyse the model contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases. By comparing these results with observations we show that the formation of the ring current is a combination of large-scale convection and pulsed inward shift and consequent energization of the ring current particles.

  2. 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

  3. 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.

  4. The pulsed nature of the nightside contribution to polar cap convection: Repetitive substorm activity under steady interplanetary driving

    Science.gov (United States)

    Sandholt, P.; Farrugia, C. J.; Andalsvik, Y.

    2012-12-01

    The aim of this study is to investigate the contributions of substorm processes to temporal structure of polar cap plasma convection. The central parameter is the cross-polar cap potential (CPCP). Selecting a ten hour-long interval of stable interplanetary driving by an interplanetary CME (ICME), we are able to distinguish between the dayside and nightside sources of the convection. The event was initiated by an abrupt enhancement of the magnetopause (MP) reconnection rate triggered by a southward turning of the ICME magnetic field. This was followed by long interval (ten hours) of steady and strong driving. Under the latter condition a long series of electrojet intensifications (polar cap contractions) was observed which recurred at 50 min. intervals. The detailed temporal structure of polar cap convection in relation to the polar cap contraction events is obtained by combining continuous ground observations of convection - related magnetic deflections (including polar cap magnetic indices in the northern and southern hemispheres, PCN and PCS) and the more direct but lower resolution ion drift data obtained from a satellite (DMSP F13) in polar orbit. The observed PCN enhancements combined with satellite observations (DMSP F13 and F15 data) of polar cap contractions during the evolution of selected substorm expansions allowed us to calculate the CPCP enhancements associated with each event in the series.

  5. 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.

  6. 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.

  7. "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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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

  17. 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...

  18. 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%.

  19. 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.

  20. 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.

  1. 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.

  2. ;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.

  3. 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.

  4. 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.

  5. 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...

  6. 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

  7. 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

  8. Spatial structure and temporal evolution of energetic particle injections in the inner magnetosphere during the 14 July 2013 substorm event

    CERN Document Server

    Gkioulidou, Matina; Mitchell, D G; Ukhorskiy, A Y; Reeves, G D; Turner, D L; Gjerloev, J W; Nosé, M; Koga, K; Rodriguez, J V; Lanzerotti, L J

    2016-01-01

    Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside geosynchronous orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm $\\textit{ Dst }$ $\\sim$ -40nT on 14 July 2013. Van Allen Probe B, inside geosynchronous orbit, observed two energetic proton injections within 10min, with different dipolarization signatures and duration. The first one is a dispersionless, short-timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer-timescale injection pulse accompanied by a gradual dipolarization signature. We combined ground magnetometer data from various stations and in situ particle and magnetic field data from multiple satellites in the inne...

  9. Generation of large-amplitude electric field and subsequent enhancement of O+ ion flux in the inner magnetosphere during substorms

    Science.gov (United States)

    Nakayama, Y.; Ebihara, Y.; Tanaka, T.

    2015-06-01

    Energetic O+ ions are rapidly enhanced in the inner magnetosphere because of abrupt intensification of the dawn-to-dusk electric field and significantly contribute to the ring current during substorms. Here we examine the generation mechanism of the dawn-to-dusk electric field that accelerates the O+ ions and the spatial and temporal evolution of the differential flux of the O+ ions by using a test particle simulation in the electric and magnetic fields that are provided by a global magnetohydrodynamics (MHD) simulation. In the MHD simulation, strong dawn-to-dusk electric field appears in the near-Earth tail region by a joint action of the earthward tension force and pileup of magnetic flux near an onset of substorm expansion. The peak of the electric field is ~9-13 mV/m and is located ~1-2 RE earthward of the peak of the plasma bulk speed because of the pileup. O+ ions coming from the lobe are accelerated from ~eV to >100 keV in ~10 min. The reconstructed flux of the O+ ions shows that at ~7 RE near midnight, the flux has a peak near a few tens of keV and the flux below ~10 keV is small. This structure, called a "void" structure, is consistent with the Polar observation and can be regarded as a manifestation of the acceleration of unmagnetized ions perpendicular to the magnetic field. In the inner magnetosphere (at 6.0 RE), reconstructed energy-time spectrograms show the nose dispersion structure that is also consistent with satellite observations.

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Electrostatic solitary waves in current layers: from Cluster observations during a super-substorm to beam experiments at the LAPD

    Directory of Open Access Journals (Sweden)

    J. S. Pickett

    2009-06-01

    Full Text Available Electrostatic Solitary Waves (ESWs have been observed by several spacecraft in the current layers of Earth's magnetosphere since 1982. ESWs are manifested as isolated pulses (one wave period in the high time resolution waveform data obtained on these spacecraft. They are thus nonlinear structures generated out of nonlinear instabilities and processes. We report the first observations of ESWs associated with the onset of a super-substorm that occurred on 24 August 2005 while the Cluster spacecraft were located in the magnetotail at around 18–19 RE and moving northward from the plasma sheet to the lobes. These ESWs were detected in the waveform data of the WBD plasma wave receiver on three of the Cluster spacecraft. The majority of the ESWs were detected about 5 min after the super-substorm onset during which time 1 the PEACE electron instrument detected significant field-aligned electron fluxes from a few 100 eV to 3.5 keV, 2 the EDI instrument detected bursts of field-aligned electron currents, 3 the FGM instrument detected substantial magnetic fluctuations and the presence of Alfvén waves, 4 the STAFF experiment detected broadband electric and magnetic waves, ion cyclotron waves and whistler mode waves, and 5 CIS detected nearly comparable densities of H+ and O+ ions and a large tailward H+ velocity. We compare the characteristics of the ESWs observed during this event to those created in the laboratory at the University of California-Los Angeles Plasma Device (LAPD with an electron beam. We find that the time durations of both space and LAPD ESWs are only slightly larger than the respective local electron plasma periods, indicating that electron, and not ion, dynamics are responsible for generation of the ESWs. We have discussed possible mechanisms for generating the ESWs in space, including the beam and kinetic Buneman type instabilities and the acoustic instabilities. Future studies will examine these mechanisms in

  5. 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

  6. Crossover behavior of multiscale fluctuations in Big Data: Langevin model and substorm time-scales in Earth's magnetosphere

    Science.gov (United States)

    Sharma, A. S.; Setty, V. A.

    2015-12-01

    Multiscale fluctuations in large and complex data are usually characterized by a power law with a scaling exponent but many systems require more than one exponent and thus exhibit crossover behavior. The scaling exponents, such as Hurst exponents, represent the nature of correlation in the system and the crossover shows the presence of more than one type of correlation. An accurate characterization of the crossover behavior is thus needed for a better understanding of the inherent correlations in the system, and is an important method of Big Data analysis. A multi-step process is developed for accurate computation of the crossover behavior. First the detrended fluctuation analysis is used to remove the trends in the data and the scaling exponents are computed. The crossover point is then computed by a Hyperbolic regression technique, with no prior assumptions. The time series data of the magnetic field variations during substorms in the Earth's magnetosphere is analyzed with these techniques and yields a crossover behavior with a time scale of ~4 hrs. A Langevin model derived from the data provides an excellent fit to the crossover in the scaling exponents and a good model of magnetospheric dynamics. The combination of fluctuation analysis and mathematical modeling thus yields a comprehensive approach in the analysis of Big Data.

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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...

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Models of field-aligned currents needful to simulate the substorm variations of the electric field and other parameters observed by EISCAT

    Directory of Open Access Journals (Sweden)

    M. A. Volkov

    Full Text Available We have used the global numerical model of the coupled ionosphere-thermosphere-protonosphere system to simulate the electric-field, ion- and electron-temperature and -concentration variations observed by EISCAT during the substorm event of 25 March 1987. In our previous studies we adopted the model input data for field-aligned currents and precipitating electron fluxes to obtain an agreement between observed and modelled ionospheric variations. Now, we have calculated the field-aligned currents needful to simulate the substrom variations of the electric field and other parameters observed by EISCAT. The calculations of the field-aligned currents have been performed by means of numerical integration of the time-dependent continuity equation for the cold magnetospheric electrons. This equation was added to the system of the modelling equations including the equation for the electric-field potential to be solved jointly. In this case the inputs of the model are the spatial and time variations of the electric-field potential at the polar-cap boundaries and those of the cold magnetospheric electron concentration which have been adopted to obtain the agreement between the observed and modelled ionospheric variations for the substorm event of 25 March 1987. By this means it has been found that during the active phase of the substorm the current wedge is formed. It is connected with the region of the decreased cold magnetospheric electron content travelling westwards with a velocity of about 1 km s–1 at ionospheric levels.

  13. Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns

    Directory of Open Access Journals (Sweden)

    J. R. Taylor

    Full Text Available The dynamic behaviour of the northern polar cap area is studied employing Northern Hemisphere electric potential patterns derived by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE procedure. The rate of change in area of the polar cap, which can be defined as the region of magnetospheric field lines open to the interplanetary magnetic field (IMF, has been calculated during two intervals when the IMF had an approximately constant southward component (1100–2200 UT, 20 March 1990 and 1300–2100 UT, 21 March 1990. The estimates of the polar cap area are based on the approximation of the polar cap boundary by the flow reversal boundary. The change in the polar cap area is then compared to the predicted expansion rate based on a simple application of Faraday's Law. Furthermore, timings of magnetospheric substorms are also related to changes in the polar cap area. Once the convection electric field reconfigures following a southward turning of the IMF, the growth rate of the observed polar cap boundary is consistent with that predicted by Faraday's Law. A delay of typically 20 min to 50 min is observed between a substorm expansion phase onset and a reduction in the polar cap area. Such a delay is consistent with a synthesis between the near Earth neutral line and current disruption models of magnetospheric substorms in which the dipolarisation in the magnetotail may act as a trigger for reconnection. These delays may represent a propagation time between near geosynchronous orbit dipolarisation and subsequent reconnection further down tail. We estimate, from these delays, that the neutral X line occurs between ~35RE and ~75RE downstream in the tail.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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...

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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

  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. 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

  9. Temporal and Spatial Evolution of Energetic Ion Injections in the Inner Magnetosphere: Multi-Point Observations of a Substorm Event.

    Science.gov (United States)

    Gkioulidou, M.; Ohtani, S.; Mitchell, D. G.; Reeves, G. D.; Ukhorskiy, A. Y.; Turner, D. L.; Gjerloev, J. W.; Nose, M.; Koga, K.; Rodriguez, J. V.; Lanzerotti, L. J.

    2014-12-01

    Plasma transport and energization of ions in the magnetotail has been shown to largely occur in the form of injections of hot plasma, localized in MLT, associated with bursty bulk flows and sharp dipolarizations of the magnetic field. However, the relationship of these transient tail phenomena to energetic particle injections into the inner magnetosphere is not well understood. Recent results by the RBSPICE instrument of the Van Allen Probes mission showed that the occurrence of energetic ion injections inside geosynchronous orbit can be very frequent throughout the main phase of a geomagnetic storm, and indicated that the contribution of such injections to the ring current buildup could be substantial. Understanding the formation and evolution of energetic ion injections in the inner magnetosphere and their relationship to transient phenomena in the tail is, therefore, of great importance. In order to differentiate between temporal and spatial variations, it is essential to investigate injections via multi-point observations. We study a substorm event that occurred during a small storm (Dst ~-40 nT), where two injections of energetic ions (50 - 300 keV), 10 minutes apart, were observed by RBSPICE instrument inside geosynchronous orbit, and six LANL and two GOES spacecraft at geosynchronous orbit. Geosynchronous spacecraft ETS-8, at a similar MLT with Van Allen Probe B, also observed the dipolarization signatures associated with these two injections. At the same time, two THEMIS spacecraft were monitoring the night-side magnetosphere at ~ 10 RE. Using ground-based magnetometer data, we are able to identify the eastward and westward edges of the current wedge associated with each one of these injections. The two injections, as observed in the inner magnetosphere, exhibit distinct differences in their dipolarization signatures as well as their duration. With all the above data at hand, we investigate the inward propagation of the injections into the inner

  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. 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.

  5. 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.

  6. 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.

  7. 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...

  8. 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.

  9. 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

  10. 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.

  11. Continuous lobe reconnection in the mid-tail and its relationship to substorms: Cluster observations of continuous lobe reconnection in the mid-magneto tail

    Institute of Scientific and Technical Information of China (English)

    CAO Xin; Q. G. Zong; H. Reme; K. H. Glassmeier; PU Zuyin; ZHANG Hui; FU Suiyan; XIAO Chijie; LIU Zhenxing; J. B. Cao; A. Korth; M. Frazen

    2005-01-01

    When the IMF turns southward, a great amount of magnetic energy is stored in the magnetotail, and the electric field across the magnetotail substantially enhances. As long as magnetic reconnection (MR) in the magnetotail initiates and continues, the magnetic field and plasma in the central plasma sheet are carried away to the near-Earth and down to the tail, the magnetic field and plasma in the lobe region enter the CPS and are involved in MR. We call this process "Continuous Lobe Reconnection (CLR)". In this paper a detailed analysis of Cluster observation of MR through 2001―2003 is made. Plenty of CLR events are found that led to considerable changes of tail configuration, appearance of BBF, as well as large-scale bubbles in which both plasma temperature and number density substantially decrease. It is shown that in general CLR events last for dozens of minutes and have good correspondence to substorm initiation under the condition of continuous southward IMF.

  12. 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

  13. 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

  14. 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.

  15. 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

  16. Adaptive systems for processing of high-dimensional and multi-scale data: Application to forecasting of geomagnetic substorms and financial time series.

    Science.gov (United States)

    Gavrishchaka, Valeriy; Ganguli, Supriya

    2001-10-01

    Predictive capabilities of the data-driven models of the systems with complex multi-scale dynamics depend on the quality and amount of the available data and on the algorithms used to extract generalized mappings. Availability of the real-time high-resolution data constantly increases in many fields of practical interest. However, the majority of advanced nonlinear algorithms, including neural networks (NN), can encounter a set of problems called "dimensionality curse" when applied to high-dimensional data. Nonstationarity of the system can also impose significant limitations on the size of training set which leads to poor generalization ability of the model. A very promising algorithm that combines the power of the best nonlinear techniques and tolerance to high-dimensional and incomplete data is support vector machine (SVM). We have summarized and demonstrated advantages of the SVM by applying it to two important and challenging problems: substorm forecasting from solar wind data and volatility forecasting from multi-scale stock and exchange market data. We have shown that performance of the SVM model for substorm prediction can be comparable to or be superior to that of the best existing models including NNs. The advantages of the SVM-based techniques are expected to be much more pronounced in future space-weather forecasting models, which will incorporate many types of high-dimensional, multi-scale input data once real-time availability of this information becomes technologically feasible. We have also demonstrated encouraging performance of the SVM in application to volatility prediction using S&P 500 stock index and USD-DM exchange rate data. Future applications of the SVM in the emerging field of high-frequency finance and its relation to existing models are also discussed.

  17. Geotail observations of energetic ion species and magnetic field in plasmoid-like structures in the course of an isolated substorm event

    Energy Technology Data Exchange (ETDEWEB)

    Zong, Q.; Wilken, B. [Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau (Germany); Reeves, G.D. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States); Daglis, I.A. [Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau (Germany)]|[Institute of Ionospheric and Space Research, National Observatory of Athens (Greece); Doke, T. [Department of Physics, Nagoya University, Nagoya (Japan); Iyemori, T. [WDC-C2 for Geomagnetism, Faculty of Science, Kyoto University, Kyoto (Japan); Livi, S. [Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau (Germany); Maezawa, K. [Advanced Research Center for Science and Engineering, Waseda University, Tokyo (Japan); Mukai, T. [Institute of Space Astronautical and Science, Kanagawa (Japan); Kokubun, S. [Solar-Terrestrial Environment Laboratory, Nagoya University, Toyokawa (Japan); Pu, Z. [Department of Geophysics, Peking University, Beijing (China); Ullaland, S. [University of Bergen, Bergen (Norway); Woch, J. [Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau (Germany); Lepping, R. [NASA Goddard Space Flight Center, Greenbelt, Maryland (United States); Yamamoto, T. [Institute of Space Astronautical and Science, Kanagawa (Japan)

    1997-06-01

    On January 15, 1994, the ion spectrometer high energy particle{endash}low energy particle detector (HEP-LD) on the Japanese spacecraft Geotail observed five quasi-periodic energetic ion bursts in the deep tail (X={minus}96R{sub E}). These bursts were associated with plasmoid-like structures in the magnetic field components. In addition, three multiple TCR groups were identified in the interval. The observations in the distant tail occurred during a time interval of substorm activity which also produced multiple injections in the geosynchronous orbit region. The HEP-LD observations show that B{sub z} bipolar plasmoid-like structures are associated with tailward flowing particle bursts. However, earthward flowing particle bursts are predominantly associated with bipolar signatures in B{sub y}. In addition, an oxygen burst was seen in the back of a plasmoid (postplasmoid) which showed both B{sub y} and B{sub z} bipolar magnetic field signatures. The oxygen burst lasted for 23 min, and the density ratio (O/H) reached 15{percent} for the HEP-LD energy range (in the same plasmoid, this ratio was approximately 1{percent} before the oxygen burst). The oxygen burst exhibited a strong beam-like structure which occupied only 6{approximately}7{percent} of the full solid angle (4{pi}). We suggest that energized oxygen ions of ionospheric origin travel downtail in the narrow postplasmoid-plasma sheet which trails the plasmoid. Furthermore, we suggest that the magnetosphere dissipated larger quantities of energy during this very intense substorm event by ejecting multiple relatively small plasmoids rather than through the formation and ejection of a single large plasmoid.{copyright} 1997 American Geophysical Union

  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. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 3D PIC Simulation of the Magnetosphere during IMF Rotation from North to South: Signatures of Substorm Triggering in the Magnetotail

    Science.gov (United States)

    Nishikawa, Ken-Ichi; Cao. D/ S/; Lembege, B.

    2008-01-01

    Three dimensional PIC simulations are performed in order to analyse the dynamics of the magnetotail as the interplanetary magnetic field (IMF) rotates from northward to southward direction. This dynamics reveals to be quite different within meridian/equatorial planes over two successive phases of this rotation. First, as IMF rotates from North to Dawn-Dusk direction, the X-Point (magnetic reconnection) evidenced in the magnetotail (meridian plane) is moving earthward (from x=-35 Re to x=-17.5 ) distance at which it stabilizes. This motion is coupled with the formation of "Crosstail-S" patterns (within the plane perpendicular to the Sun-Earth mine) through the neutral sheet in the nearby magnetotail. Second, as IMF rotates from dawn-dusk to South, the minimum B field region is expanding within the equatorial plane and forms a ring. This two-steps dynamics is analyzed in strong association with the cross field magnetotail current Jy, in order to recover the signatures of substorms triggering.

  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. Two Wide-Angle Imaging Neutral-Atom Spectrometers and Interstellar Boundary Explorer energetic neutral atom imaging of the 5 April 2010 substorm

    Science.gov (United States)

    McComas, D. J.; Buzulukova, N.; Connors, M. G.; Dayeh, M. A.; Goldstein, J.; Funsten, H. O.; Fuselier, S.; Schwadron, N. A.; Valek, P.

    2012-03-01

    This study is the first to combine energetic neutral atom (ENA) observations from Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) and Interstellar Boundary Explorer (IBEX). Here we examine the arrival of an interplanetary shock and the subsequent geomagnetically effective substorm on 5 April 2010, which was associated with the Galaxy 15 communications satellite anomaly. IBEX shows sharply enhanced ENA emissions immediately upon compression of the dayside magnetosphere at 08:26:17+/-9 s UT. The compression drove a markedly different spectral shape for the dayside emissions, with a strong enhancement at energies >1 keV, which persisted for hours after the shock arrival, consistent with the higher solar wind speed, density, and dynamic pressure (˜10 nPa) after the shock. TWINS ENA observations indicate a slower response of the ring current and precipitation of ring current ions as low-altitude emissions ˜15 min later, with the >50 keV ion precipitation leading the internal magnetospheric processes are occurring after compression of the magnetosphere and before the ring current ions end up in the loss cone and precipitate into the ionosphere. We also compare MHD simulation results with both the TWINS and IBEX ENA observations; while the overall fluxes and distributions of emissions were generally similar, there were significant quantitative differences. Such differences emphasize the complexity of the magnetospheric system and importance of the global perspective for macroscopic magnetospheric studies. Finally, Appendix A documents important details of the TWINS data processing, including improved binning procedures, smoothing of images to a given level of statistical accuracy, and differential background subtraction.

  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. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Motion of the dayside polar cap boundary during substorm cycles: II. Generation of poleward-moving events and polar cap patches by pulses in the magnetopause reconnection rate

    Directory of Open Access Journals (Sweden)

    M. Lockwood

    2005-12-01

    Full Text Available Using data from the EISCAT (European Incoherent Scatter VHF and CUTLASS (Co-operative UK Twin-Located Auroral Sounding System HF radars, we study the formation of ionospheric polar cap patches and their relationship to the magnetopause reconnection pulses identified in the companion paper by Lockwood et al. (2005. It is shown that the poleward-moving, high-concentration plasma patches observed in the ionosphere by EISCAT on 23 November 1999, as reported by Davies et al. (2002, were often associated with corresponding reconnection rate pulses. However, not all such pulses generated a patch and only within a limited MLT range (11:00-12:00 MLT did a patch result from a reconnection pulse. Three proposed mechanisms for the production of patches, and of the concentration minima that separate them, are analysed and evaluated: (1 concentration enhancement within the patches by cusp/cleft precipitation; (2 plasma depletion in the minima between the patches by fast plasma flows; and (3 intermittent injection of photoionisation-enhanced plasma into the polar cap. We devise a test to distinguish between the effects of these mechanisms. Some of the events repeat too frequently to apply the test. Others have sufficiently long repeat periods and mechanism (3 is shown to be the only explanation of three of the longer-lived patches seen on this day. However, effect (2 also appears to contribute to some events. We conclude that plasma concentration gradients on the edges of the larger patches arise mainly from local time variations in the subauroral plasma, via the mechanism proposed by Lockwood et al. (2000.

  7. 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.

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. Ionospheric characteristics of the dusk-side branch of the two-cell aurora

    Directory of Open Access Journals (Sweden)

    J.-H. Shue

    2006-03-01

    Full Text Available The two-cell aurora is characterized by azimuthally elongated regions of enhanced auroral brightness over extended local times in the dawn and dusk sectors. Its association with the convection, particle precipitation, and field-aligned currents under various phases of substorms has not been fully understood. With Polar Ultraviolet Imager auroral images in conjunction with Defense Meteorological Satellite Program (DMSP F12 spacecraft on the dusk-side branch of the two-cell aurora, we are able to investigate an association of the auroral emissions with the electric fields, field-aligned currents, and energy flux of electrons. Results show that the substorm expansion onset does not significantly change the orientation of the dusk-side branch of the two-cell aurora. Also, the orientation of the magnetic deflection vector produced by the region 1 field-aligned current changed from 73±1° to the DMSP trajectory during the substorm growth phase, to 44±6° to the DMSP trajectory during the substorm expansion phase. With a comparison between the orientation of the dusk-side branch of the two-cell aurora and the orientation of the magnetic deflection vector, it is found that the angular difference between the two orientations is 28±5° during the substorm growth phase, and 13±6° during the substorm expansion phase.

  5. 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.

  6. 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.

  7. 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.

  8. Periodic Substorm Activity in the Geomagnetic Tail.

    Science.gov (United States)

    1983-02-01

    The electron intensities appear to be iso- tropic , while the ions exhibit a weak anisotropy. The bulk of the plasma may be present below 215 eV and...G. K. Parks, C. S. Lin, H. Reme, J. M. Bosqued , F. Martel, F. Cotin and A. Cros, An experiment to study energetic particle fluxes in and beyond the

  9. 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...

  10. 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

  11. 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.

  12. Dual HF radar study of the subauroral polarization stream

    Directory of Open Access Journals (Sweden)

    R. A. Makarevich

    2008-01-01

    Full Text Available The dual HF radars comprising the Tasman International Geophysical Environment Radar (TIGER system often observe localized high-velocity F-region plasma flows (≥1500 m/s in the midnight sector (20:00–02:00 MLT at magnetic latitudes as low as Λ=60° S. The flow channels exhibit large variability in the latitudinal extent and electric field strength, and are similar to the subauroral polarization stream or SAPS, a plasma convection feature thought to be related to the polarization electric field due to the charge separation during substorm and storm development. In this study, the 2-D plasma drift velocity within the channel is derived for each of the two TIGER radars from the maximum velocities measured in all 16 radar beams within the latitudinally narrow channel, and the time variation of the subauroral electric field is examined near substorm onset. It is demonstrated that the flow channel often does not have a clear onset, rather it manifests differently in different phases of its evolution and can persist for at least two substorm cycles. During the growth phase the electric fields within the flow channel are difficult to distinguish from those of the background auroral convection but they start to increase near substorm onset and peak during the recovery phase, in contrast to what has been reported previously for auroral convection which peaks just before the substorm onset and falls sharply at the substorm onset. The response times to substorm onset range from −5 to +40 min and show some dependence on the substorm location with longer delays observed for substorms eastward of the radars' viewing area. The propagation velocity of the high-velocity region is also investigated by comparing the observations from the two closely-spaced TIGER radars. The observations are consistent with the notion that the polarization electric field is established with the energetic ions drifting westward and equatorward from the initial substorm

  13. 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.

  14. Active probing of space plasmas

    Science.gov (United States)

    Chan, Chang; Silevitch, Michael B.; Villalon, Elena

    1989-09-01

    During the course of the research period our efforts were focused on the following areas: (1) An examination of stochastic acceleration mechanisms in the ionosphere; (2) A study of nonequilibrium dynamics of the coupled magnetosphere - ionosphere system; and (3) Laboratory studies of active space experiments. Reprints include: Dynamics of charged particles in the near wake of a very negatively charged body -- Laboratory experiment and numerical simulation; Laboratory study of the electron temperature in the near wake of a conducting body; New model for auroral breakup during substorms; Substorm breakup on closed field lines; New model for substorm on sets -- The pre-breakup and triggering regimes; Model of the westward traveling surge and the generation of Pi 2 pulsations; Ionospheric electron acceleration by electromagnetic waves near regions of plasma resonances; Relativistic particle acceleration by obliquely propagating electromagnetic fields; Some consequences of intense electromagnetic wave injection into space plasmas.

  15. Active probing of space plasmas. Final report, 25 October 1985-30 September 1989

    Energy Technology Data Exchange (ETDEWEB)

    Chan, C.; Silevitch, M.B.; Villalon, E.

    1989-09-01

    During the course of the research period our efforts were focused on the following areas: (1) An examination of stochastic acceleration mechanisms in the ionosphere; (2) A study of nonequilibrium dynamics of the coupled magnetosphere - ionosphere system; and (3) Laboratory studies of active space experiments. Reprints include: Dynamics of charged particles in the near wake of a very negatively charged body -- Laboratory experiment and numerical simulation; Laboratory study of the electron temperature in the near wake of a conducting body; New model for auroral breakup during substorms; Substorm breakup on closed field lines; New model for substorm on sets -- The pre-breakup and triggering regimes; Model of the westward traveling surge and the generation of Pi 2 pulsations; Ionospheric electron acceleration by electromagnetic waves near regions of plasma resonances; Relativistic particle acceleration by obliquely propagating electromagnetic fields; Some consequences of intense electromagnetic wave injection into space plasmas.

  16. The aurora and the magnetosphere - The Chapman Memorial Lecture. [dynamo theory development, 1600-present

    Science.gov (United States)

    Akasofu, S.-I.

    1974-01-01

    Review of recent progress in magnetospheric physics, in particular, in understanding the magnetospheric substorm. It is shown that a number of magnetospheric phenomena can now be understood by viewing the solar wind-magnetosphere interaction as an MHD dynamo; auroral phenomena are powered by the dynamo. Also, magnetospheric responses to variations of the north-south and east-west components of the interplanetary magnetic field have been identified. The magnetospheric substorm is entirely different from the responses of the magnetosphere to the southward component of the interplanetary magnetic field. It may be associated with the formation of a neutral line within the plasma sheet and with an enhanced reconnection along the line. A number of substorm-associated phenomena can be understood by noting that the new neutral line formation is caused by a short-circuiting of a part of the magnetotail current.

  17. 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.

  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. Discrete auroras and magnetotail processes.

    Science.gov (United States)

    Lyons, L. R.

    Important information about magnetospheric phenomena associated with auroras and substorms can be inferred from low-altitude auroral observations. Satellite observations have shown that discrete auroral arcs lie within a boundary plasma sheet (BPS) region that is outside the central plasma sheet (CPS). The observations imply that arcs are generated along BPS field lines by magnetospheric processes that form large, perpendicular electric field structures. The BPS and the arc generation processes apparently lie along field lines that are in the vicinity of the boundary between open and closed field lines and cross the tail (or magnetopause) current sheet. Ground-based observations show that the first indication of a substorm onset is the brightening of a quiet, discrete arc. This suggests that substorms are initiated along the BPS field lines associated with arc generation, and not within the CPS. Finally, auroral observations have shown that the area of open, polar-cap field lines varies considerably during periods of geomagnetic activity. Expansion of the polar cap has the potential for releasing trapped plasma sheet particles along freshly open field lines. The resulting evacuation of field lines has the potential for being an important loss process for the plasma sheet and for being a source of tailward flows and energetic particle bursts in the tail.

  20. Substorm activity in Venus's magnetotail

    Directory of Open Access Journals (Sweden)

    M. Volwerk

    2009-06-01

    Full Text Available The magnetotail of the induced magnetosphere of Venus is investigated through the magnetic field and plasma data of Venus Express. A comparison is made between two neutral sheet crossings. One crossing shows the magnetic field is rather quiet and the plasma instrument indicates a change from energetic (few 100 eV to low energy (few 10 eV ions. The other crossing shows more dynamics in the magnetic field, including signatures that are interpreted as characteristic of a reconnection site, and the plasma instrument indicates ions that are energized to 1500 to 2000 eV, in the same magnetospheric region where in the first crossing only low energy ions showed up.

  1. Source Determination for Substorm-Related Ion Injections

    Science.gov (United States)

    Strangeway, Robert J.; Evans, David (Technical Monitor)

    2001-01-01

    The grant supported an effort to restore and analyze data from the Spacecraft Charging at High Altitude (SCATHA) spacecraft. This spacecraft, which was originally an Air Force mission, was launched into a near geo-synchronous orbit in early 1979 to, investigate the inner magnetosphere at altitudes where it was known that spacecraft can undergo significant charging events. SCATHA included an ion composition experiment (designated SC8) and in many ways was a precursor to other missions, such as the AMPTE Charge Composition Explorer.

  2. 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...

  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. 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

  5. Evaluation on the analogy between the dynamic magnetosphere and a forced and/or self-organized critical system

    Directory of Open Access Journals (Sweden)

    A. T. Y. Lui

    2002-01-01

    Full Text Available The dissipation power and size of auroral blobs are investigated in detail to examine the possible analogy between the dynamic magnetosphere and a forced and/or self-organized critical system. The distributions of these auroral parameters are sorted in terms of different levels of activity, namely substorms, pseudo-breakups, and quiet conditions. A power law (scale-free component is seen in all these distributions. In addition, a peak distribution is found for substorm intervals and a hump for pseudo-breakup intervals. The peak distribution is present prominently during magnetic storms, i.e. when the magnetosphere is strongly driven by the solar wind. It is interpreted that the scale-free component is associated with the activity of the diffuse aurora, corresponding to disturbances at all permissible scales within the plasma sheet. Ionospheric feedback appears to be essential for the presence of two components in the distribution for auroral dissipation power. These results are consistent with the concept that the magnetosphere is in a forced and/or self-organized critical state, although they do not constitute conclusive evidence for the analogy.

  6. Catapult current sheet relaxation model confirmed by THEMIS observations

    Science.gov (United States)

    Machida, S.; Miyashita, Y.; Ieda, A.; Nose, M.; Angelopoulos, V.; McFadden, J. P.

    2014-12-01

    In this study, we show the result of superposed epoch analysis on the THEMIS probe data during the period from November, 2007 to April, 2009 by setting the origin of time axis to the substorm onset determined by Nishimura with THEMIS all sky imager (THEMS/ASI) data (http://www.atmos.ucla.edu/~toshi/files/paper/Toshi_THEMIS_GBO_list_distribution.xls). We confirmed the presence of earthward flows which can be associated with north-south auroral streamers during the substorm growth phase. At around X = -12 Earth radii (Re), the northward magnetic field and its elevation angle decreased markedly approximately 4 min before substorm onset. A northward magnetic-field increase associated with pre-onset earthward flows was found at around X = -17Re. This variation indicates the occurrence of the local depolarization. Interestingly, in the region earthwards of X = -18Re, earthward flows in the central plasma sheet (CPS) reduced significantly about 3min before substorm onset. However, the earthward flows enhanced again at t = -60 sec in the region around X = -14 Re, and they moved toward the Earth. At t = 0, the dipolarization of the magnetic field started at X ~ -10 Re, and simultaneously the magnetic reconnection started at X ~ -20 Re. Synthesizing these results, we can confirm the validity of our catapult current sheet relaxation model.

  7. 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.

  8. 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.

  9. 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

  10. On the dissociation of nitrogen by electron impact and by EUV photo-absorption. [in aurorqs

    Science.gov (United States)

    Zipf, E. C.; Mclaughlin, R. W.

    1978-01-01

    The dissociation of N2 by electron impact and by absorption of EUV photons was studied experimentally. It was shown that most of the N2 molecules excited to singlet states in the 12.5-14.86 eV range are depopulated by predissociation and not by the emission of EUV photons and that this is the principal mechanism by which N2 is dissociated by solar EUV absorption and by electron impact. The experiments provide a physical explanation for the near absence of N2 band radiation in airglow and auroral EUV spectra, and rule out the excitation of EUV radiation as a major factor in the overall energy economy of an auroral substorm.

  11. Exploring the Secrets of the Aurora Second Edition

    CERN Document Server

    Akasofu, Syun-Ichi

    2007-01-01

    This new edition of Exploring the Secrets of the Aurora is based on the author's own experiences as a scientist. It describes the history of progress made in auroral science and magnetospheric physics by providing examples of ideas, controversies, struggles, acceptance, and success. Although no general methodologies are mentioned, the hope is that the reader will learn about the history of progress in auroral science and examples of dealing with the many controversies. This book aims to help young scientific researchers learn how to persevere during periods of controversy and struggles for acceptance. In this second edition, by utilizing multiple examples, Akasofu is successful in demonstrating the importance and usefulness of Synthesis. "Probably the book's most valuable contribution to the history of space physics is precisely the narration of the discovery of substorms.---The book has special features.---Akasofu's coverage of the history of pre-space age solar-terrestrial relations is the most comprehensiv...

  12. Intermittency on simultaneous observations of riometer at several Antarctic locations

    Science.gov (United States)

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

    2016-03-01

    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 night-time 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, we analyse simultaneous observations of riometer absorption at seven Antarctic locations, to determine whether they exhibit intermittency. We determine the Probability Distribution Functions of the fluctuations of riometer absorption for absorption events larger than 0.1 dB, as well as those for the time-intervals between absorption events. Observations are for locations within the austral auroral absorption zone and on the polar cap. It is found that the parameters of a power law used to describe the calculated PDFs are consistent with the formation of coherent structures being more frequent within the auroral zone, as a manifestation of intermittency.

  13. Phase fluctuations of GPS signals and irregularities in the high latitude ionosphere during geomagnetic storm

    Science.gov (United States)

    Shagimuratov, I.; Chernouss, S.; Cherniak, Iu.; Efishov, I.; Filatov, M.; Tepenitsyna, N.

    2016-05-01

    In this report we analysed latitudinal occurrence of TEC fluctuations over Europe during October 2, 2013 geomagnetic storm. The data of GPS stations spaced in latitudinal range 68°-54° N over longitude of 20°E were involved in this investigation. The magnetograms of the IMAGE network and geomagnetic pulsations at Lovozero (68°02'N 35°00'W) and Sodankyla (67°22'N 26°38'W) observatories were used as indicator of auroral activity. During October 2, 2013 the strong geomagnetic field variations took place near 05 UT at auroral IMAGE network. We found good similarities between time development of substorm and fluctuations of GPS signals. The bay-like geomagnetic variations were followed by intensive phase fluctuations at auroral and subauroral stations. The strong short-term phase fluctuations were also found at mid-latitude Kaliningrad station near 05 UT that correspond to the maximal intense geomagnetic bay variations. This date confirms the equatorward expansion of the auroral oval. It brings in evidence also the storm time behavior of the irregularities oval obtained from multi-site GPS observations.

  14. The Linkage Between the Ionospheric Trough and Ring Current

    Science.gov (United States)

    Brandt, P. C.; Zheng, Y.; Talaat, E.; Sotirelis, T.; Foster, J. C.; Erickson, P. J.

    2007-05-01

    We present data-model investigations of how the ring current couples to the sub-auroral ionosphere. The ring current pressure distribution during storm and substorms is highly asymetrical and sets up the region 2 current system that closes through the sub-auroral ionosphere. Of particular interest is what happens in the so-called ionospheric trough region, which is a region in the evening ionosphere with extremely low conductance (few tenths of a mho). Observations show strong westward flows in the ionospheric trough (Sub-Auroral Polarization Stream - SAPS) and sometimes highly structured and variable. The Comprehensive Ring Current Model models the ring current by using the bounce averaged Boltzmann equation and allowing the ring current to close through the ionosphere. Our model ionosphere includes dayside and auroral conductance as well as semi-empirical representation of the trough conductance. By using realistic representations of the conductances we seek to explore how the ring current pressure distribution (and therefore the region 2 current system) is linked to the presence of the trough. We use data from the IMAGE satellite, the Millstone Hill and SuperDARN radar facilities.

  15. 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

  16. 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.

  17. 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

  18. 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...

  19. 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.

  20. 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.

  1. 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...

  2. 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.

  3. Comment on Decay of the Dst Field of Geomagnetic Disturbance After Substorm Onset and its Implication to Storm-Substorm Relation

    Science.gov (United States)

    Rostoker, G.; Baumjohann, W.; Gonzalez, W.; Kamide, Y.; Kokubun, S.; McPherron, R. L.; Tsurutani, B. T.

    1996-01-01

    Over the past few years, there has been a considerable revival in the study of geomagnetic storms stimulated by an increasing knowledge of the energetic particles which comprise the ring current. It is only in recent years that the composition of the ring current has been thouroughly explored and the important role of the oxygen component of the near Earth plasma sheet has become recognized.

  4. Continuous tailward flow in the near-Earth magnetotail observed by TC-1 satellite

    Institute of Scientific and Technical Information of China (English)

    ZHANG LingQian; LIU ZhenXing; MA ZhiWei; PU ZuYin; WANG JiYe; SHEN Chao

    2007-01-01

    On July 11, 2004, a substorm process in the period of continuou