Sample records for auroral substorms

  1. The convection electric field in auroral substorms

    Gjerløv, Jesper Wittendorff; Hoffman, R.A.


    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...... this database enabled us to compile a model of the ionospheric convection electric field. The characteristics of the premidnight convection reversal show a pronounced local time dependency. Far west of the surge it is a fairly well defined point reversal or convection shear. Approaching the surge and within...... the surge it is a region of weak electric fields increasing in width toward midnight that separates regions of equatorward and poleward electric fields. Therefore we adopt the term Harang region rather than the Harang discontinuity for the premidnight convection reversal. A relatively narrow convection...

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

    Gjerløv, Jesper Wittendorff; Hoffman, R.A.

    We present height-integrated Hall and Pedersen conductivity (conductance) calculations from 31 individual Dynamics Explorer 2 (DE 2) substorm crossings. All are northern hemisphere (except one) nighttime passes which took place from September 1981 to January 1982. Global auroral images are used 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...

  3. Response of northern winter polar cap to auroral substorms

    Liou, Kan; Sotirelis, Thomas


    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.

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

    Gjerløv, Jesper Wittendorff; Hoffman, R.A.

    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...

  5. Variations of auroral hydrogen emission near substorm onset

    L. P. Borovkov


    Full Text Available The results of coordinated optical ground-based observations of the auroral substorm on 26 March 2004 in the Kola Peninsula are described. Imaging spectrograph data with high spectral and temporal resolution recorded the Doppler profile of the Hα hydrogen emission; this allows us to estimate the average energy of precipitating protons and the emission intensity of the hydrogen Balmer line. Two different populations of precipitating protons were observed during an auroral substorm. The first of these is associated with a diffuse hydrogen emission that is usually observed in the evening sector of the auroral oval and located equatorward of the discrete electron arcs associated with substorm onset. The average energy of the protons during this precipitation was ~20–35 keV, and the energy flux was ~3x10–4Joule/m2s. The second proton population was observed 1–2min after the breakup during 4–5min of the expansion phase of substorm into the zone of bright, discrete auroral structures (N-S arcs. The average energy of the protons in this population was ~60 keV, and the energy flux was ~2.2x10–3Joule/m2s. The observed spatial structure of hydrogen emission is additional evidence of the higher energy of precipitated protons in the second population, relative to the protons in the diffuse aurora. We believe that the most probable mechanism of precipitation of the second population protons was pitch-angle scattering of particles due to non-adiabatic motion in the region of local dipolarization near the equatorial plane.

    Keywords. Auroral ionosphere; Particle precipitation; Storms and substorms

  6. Observations of magnetic field dipolarization during auroral substorm onset

    Frank, L. A.; Paterson, W. R.; Sigwarth, J. B.; Kokubun, S.


    The dynamical behavior of plasmas and magnetic fields in the vicinity of the equatorial crossing of magnetic field lines threading the onset auroral arc is examined for two substorms on November 26, 1997. The locations of the initial brightenings of the auroral arcs were determined with the cameras for visible and far-ultraviolet wavelengths on board the Polar spacecraft. The equatorial positions of the field lines were in the range of radial distances of 8-12RE as computed with models of Earth's global magnetic field. The radial distance of the Geotail spacecraft was 14 RE at a position in the premidnight sector that was 2RE below the current sheet. This spacecraft was embedded in a low-β plasma that was located adjacent to the central hot plasma sheet. For the first substorm, with onset at 1310 UT, no substantial effect was observed in the plasmas and magnetic fields, although the Geotail spacecraft was located only about 2 hours in magnetic local time from the field lines threading the onset auroral arc. For the second substorm onset, at 1354 UT, the spacecraft was positioned within tens of minutes in local time of the position of the magnetic field lines threading the onset auroral arc. This fortuitous spacecraft position in the relatively quiescent plasma and magnetic fields adjacent to the central plasma sheet and within several Earth radii of the position of the onset mechanism allowed determination of the beginning time of the dipolarization of the magnetic fields. This time was simultaneous with the onset brightening of the auroral arc within the approximately 1-min time resolution of the auroral images. The simultaneity of the initial brightening of the auroral arc and of the initiation of the dipolarization of the magnetic field, presumably due to diversion of current from the equatorial current sheet to the ionosphere, provides an important guideline for global dynamical MHD models of Earth's magnetosphere.

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

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


    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...

  8. Plasma sheet fast flows and auroral dynamics during substorm: a case study

    N. L. Borodkova

    Full Text Available Interball-1 observations of a substorm development in the mid-tail on 16 December 1998 are compared with the auroral dynamics obtained from the Polar UV imager. Using these data, the relationship between plasma flow directions in the tail and the location of the auroral activation is examined. Main attention is given to tailward and earth-ward plasma flows, interpreted as signatures of a Near Earth Neutral Line (NENL. It is unambiguously shown that in the mid-plasma sheet the flows were directed tailward when the auroral bulge developed equatorward of the spacecraft ionospheric footprint. On the contrary, when active auroras moved poleward of the Interball-1 projection, earthward fast flow bursts were observed. This confirms the concept that the NENL (or flow reversal region is the source of auroras forming the poleward edge of the auroral bulge. The observed earthward flow bursts have all typical signatures of Bursty Bulk Flows (BBFs, described by Angelopolous et al. (1992. These BBFs are related to substorm activations starting at the poleward edge of the expanded auroral bulge. We interpret the BBFs as a result of reconnection pulses occurring tail-ward of Interball-1. In addition, some non-typically observed phenomena were detected in the plasma sheet during this substorm: (i tailward/earthward flows were superimposed on a very strong duskward flow, and (ii wavy structures of both magnetic field and plasma density were registered. The latter observation is probably linked to the filamentary structure of the current sheet.

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

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

    A. Grocott


    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

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

    Grocott, A.; Lester, M.; Parkinson, M. L.; Yeoman, T. K.; Dyson, P. L.; Devlin, J. C.; Frey, H. U.


    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 way which has

  11. Dependence of substorm occurrence probability on the interplanetary magnetic field and on the size of the auroral oval

    The dependence of substorm occurrence probability on the north--south component Bz of the interplanetary magnetic field (IMF) and on the size of the auroral oval is examined on the basis of two independent data sets (Isis 1 and 2 low-energy electron data and all-sky camera data from the Alaska meridan). The occurrence of substorms is identified by the electron precipitation pattern (Isis data), the auroral features in the Alaskan sector, and available ground magnetic records. The substorm occurrence frequency increases as the oval expands and as the Bz component of the IMF decreases. It increases from approximately 25% to 100% for Bz values of the IMF ranging from +7 to -5 nT; here Bz values are averaged for 1 hour preceding the time of satellite passage and the onset of substorms observed by the all-sky cameras. The occurrence probability of quiet times increases with an increasing value of the northward IMF. It is interesting to note that there are almost no periods without substorms when the IMF has a large southward component, but substorms do occur even when the IMF has a large northward component. Since there is a close relationship between the direction of the IMF and the size of the auroral oval, our finding that the occurrence frequency of substorms increases with the expansion of the auroral oval suggests that the substorm probability may be related to the amount of energy stored in the magnetotail

  12. Shape-Constrained Sparse and Low-Rank Decomposition for Auroral Substorm Detection.

    Yang, Xi; Gao, Xinbo; Tao, Dacheng; Li, Xuelong; Han, Bing; Li, Jie


    An auroral substorm is an important geophysical phenomenon that reflects the interaction between the solar wind and the Earth's magnetosphere. Detecting substorms is of practical significance in order to prevent disruption to communication and global positioning systems. However, existing detection methods can be inaccurate or require time-consuming manual analysis and are therefore impractical for large-scale data sets. In this paper, we propose an automatic auroral substorm detection method based on a shape-constrained sparse and low-rank decomposition (SCSLD) framework. Our method automatically detects real substorm onsets in large-scale aurora sequences, which overcomes the limitations of manual detection. To reduce noise interference inherent in current SLD methods, we introduce a shape constraint to force the noise to be assigned to the low-rank part (stationary background), thus ensuring the accuracy of the sparse part (moving object) and improving the performance. Experiments conducted on aurora sequences in solar cycle 23 (1996-2008) show that the proposed SCSLD method achieves good performance for motion analysis of aurora sequences. Moreover, the obtained results are highly consistent with manual analysis, suggesting that the proposed automatic method is useful and effective in practice. PMID:25826810

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

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


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

    Gjerløv, Jesper Wittendorff; Hoffman, R.A.


    are highly localized with a typical scale size of similar to 20 km and are associated with energetic (>10 keV) inverted V events. Except in the low-latitude part of the auroral oval the Hall to Pedersen ratio equals or exceeds 1.0, and it peaks in the high-latitude part of the surge where values of 3...

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

    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. Global Auroral Energy Deposition during Substorm Onset Compared with Local Time and Solar Wind IMF Conditions

    Spann, J. F.; Brittnacher, M.; Fillingim, M. O.; Germany, G. A.; Parks, G. K.


    The global images made by the Ultraviolet Imager (UVI) aboard the IASTP/Polar Satellite are used to derive the global auroral energy deposited in the ionosphere resulting from electron precipitation. During a substorm onset, the energy deposited and its location in local time are compared to the solar wind IMF conditions. Previously, insitu measurements of low orbiting satellites have made precipitating particle measurements along the spacecraft track and global images of the auroral zone, without the ability to quantify energy parameters, have been available. However, usage of the high temporal, spatial, and spectral resolution of consecutive UVI images enables quantitative measurement of the energy deposited in the ionosphere not previously available on a global scale. Data over an extended period beginning in January 1997 will be presented.

  17. Substorm related changes in precipitation in the dayside auroral zone – a multi instrument case study

    A. J. Kavanagh

    Full Text Available A period (08:10–14:40 MLT, 11 February 1997 of enhanced electron density in the D- and E-regions is investigated using EISCAT, IRIS and other complementary instruments. The precipitation is determined to be due to substorm processes occurring close to magnetic midnight. Energetic electrons drift eastward after substorm injection and precipitate in the morning sector. The precipitation is triggered by small pulses in the solar wind pressure, which drive wave particle interactions. The characteristic energy of precipitation is inferred from drift timing on different L-shells and apparently verified by EISCAT measurements. The IMF influence on the precipitation in the auroral zone is also briefly discussed. A large change in the precipitation spectrum is attributed to increased numbers of ions and much reduced electron fluxes. These are detected by a close passing DMSP satellite. The possibility that these ions are from the low latitude boundary layer (LLBL is discussed with reference to structured narrow band Pc1 waves observed by a search coil magnetometer, co-located with IRIS. The intensity of the waves grows with increased distance equatorward of the cusp position (determined by both satellite and HF radar, contrary to expectations if the precipitation is linked to the LLBL. It is suggested that the ion precipitation is, instead, due to the recovery phase of a small geomagnetic storm, following on from very active conditions. The movement of absorption in the later stages of the event is compared with observations of the ionospheric convection velocities. A good agreement is found to exist in this time interval suggesting that E × B drift has become the dominant drift mechanism over the gradient-curvature drift separation of the moving absorption patches observed at the beginning of the morning precipitation event.

    Key words. Ionosphere (auroral ionosphere; particle precipitation Magnetospheric physics (storms and substorms

  18. Composite imaging of convective flows and auroral forms during a substorm cycle

    Semeter, J. L.; Butler, T.; Zettergren, M. D.; Nicolls, M. J.; Heinselman, C. J.


    Measurements obtained with the electronically steerable Poker Flat Incoherent Scatter Radar (PFISR) and a collocated all-sky camera have been used to construct composite images of ionospheric convective flows and auroral forms associated with an isolated substorm on 26 March 2008. The radar was configured to cycle through a 5x5 grid of beam positions. A statistical inversion of line-of-sight velocities was used to construct images of the overlying flow field at 30-km spatial resolution and 1-min time resolution over a 100x100-km field. The flow fields were co-registered with all-sky images recorded at 20-s cadence. Analysis of the composite images has revealed several interesting contrasts between growth-, expansion-, and recover-phase morphology. These include, (1) anti-correlation between ion velocity (electric field) and luminosity (plasma density, hence, conductance) in space and time during growth- and expansion-phases; identical velocities inside and outside the aurora during recovery phase, (2) large tangential velocity directed along auroral boundaries during all phases (consistent with electric field directed into the aurora), irrespective of the orientation of the arc boundary, and (3) large relative drift (~2 km/s) between aurora forms and convective flows during the recovery phase; little or no proper motion during growth phase. The results are interpreted with respect to electrodynamic models of auroral M-I coupling. Composite image showing convective flows (arrows), ion temperature at 200 km (contours), and auroral forms at onset of a pseudo-breakup event.

  19. Substorm processes in the geomagnetic tail and their effect in the nightside auroral zone ionosphere as observed by EISCAT

    Current understanding of magnetospheric substorms is reviewed with special emphasis on the relation between space-based and ground-based observations. Traditional means of monitoring substorms from the ground (by using magnetometers, riometers and auroral observations) give only a selective picture of the whole phenomenon, related to the precipitation of electrons with energies above 1 keV. Measurements by incoherent scatter radar, such as the European incoherent scatter facility (EISCAT), give a more complete and continuous picture. The 'neutral line' model of substorms provides a natural, physical basis on which relevant data can be interpreted. In this picture, two sources of flow are anticipated in the nightside auroral zones, one 'directly driven' (with a delay of 15-20 min) by the interplanetary magnetic field (IMF) Bz component and associated with dayside reconnection, and the other appearing typically an hour after southward turnings of the IMF and associated with rapid tail reconnection during substorms. Evidence for the influence of both sources of flow is found in nightside EISCAT data. These data also reveal that, overall, the nightside ionospheric flow and plasma parameters often vary in a quasi-periodic way with a period of ca. 1 h. In two cases in which concurrent interplanetary data are available it appears that the periodicity is inherent in IMF Bz, but this is not expressed unmodified in the auroral zone because of the presence of the two sources of flow which depend on IMF Bz in different ways. (author)

  20. Inductive electric fields in the magnetotail and their relation to auroral and substorm phenomena

    The paper reviews the importance of inductive electric fields in explaining different magnetospheric and auroral phenomena during moderately and highly distrubed conditions. Quiet-time particle energization and temporal development of the tail structure during the substorm growth phase are explained by the presence of a large-scale elctrostatic field directed from dawn to dusk over the magentotail. Conservation of the first adiabatic invariant in the neutral sheet with a small value of the gradient in the magnetic field implies that the longitudical energy increases at each crossing of the neutral sheet. At a certain moment, this may result in a rapid local growth of the current and in an instability that triggers the onset. During the growth phase energy is stored in the magnetic field, since the energy density in the electric field is negligible compared to that of the magnetic field. An analytical model is described in which the characteristic observations of a substorm onset are taken into account. One major feature is that the triggering is confined to a small local time sector. During moderate disturbances, the induction fields in the magnetotail are stronger by at least one order of magnitude than the average cross-tail field. Temporal development of the disturbed area results in X- and O-type neutral lines. Particles near to these neutral lines are energized to over 1 MeV energies within a few seconds, due to an effective combination of linear and betatron acceleration. The rotational property of the induction field promotes energization in a restricted area wiht dimensions equivalent to a few Earth's radii. The model also predicts the existence of highly localized cable-type field-aligned currents appearing on the eastern and western edges of the expanding auroral bulge

  1. Equivalent currents associated with morning-sector geomagnetic Pc5 pulsations during auroral substorms

    Kauristie, K.; Uspensky, M. V.; Kleimenova, N. G.; Kozyreva, O. V.; Van De Kamp, M. M. J. L.; Dubyagin, S. V.; Massetti, S.


    Space and time variations of equivalent currents during morning-sector Pc5 pulsations (T ˜ 2-8 min) on 2 days (18 January and 19 February 2008) are studied in the context of substorm activity with THEMIS and MIRACLE ground-based instruments and THEMIS P3, P5, and P2 probes. These instruments covered the 22:00-07:00 magnetic local time during the analyzed events. In these cases abrupt changes in the Pc5 amplitudes, intensifications and/or weakenings, were recorded some minutes after auroral breakups in the midnight sector. We analyze three examples of Pc5 changes with the goal to resolve whether substorm activity can have an effect on Pc5 amplitude or not. In two cases (on 19 February) the most likely explanation for Pc5 amplitude changes comes from the solar wind (changes in the sign of interplanetary magnetic field Bz). In the third case (on 18 January) equivalent current patterns in the morning sector show an antisunward-propagating vortex which replaced the Pc5-related smaller vortices and consequently the pulsations weakened. We associate the large vortex with a field-aligned current system due to a sudden, although small, drop in solar wind pressure (from 1 to 0.2 nPa). However, the potential impact of midnight substorm activity cannot be totally excluded in this case, because enhanced fluxes of electrons with high enough energies (˜ 280 keV) to reach the region of Pc5 within the observed delay were observed by THEMIS P2 at longitudes between the midnight and morning-sector instrumentation.

  2. Equatorial ionospheric response to isolated auroral substorms over a solar cycle (1980-85): evidence of longitudinal anomaly

    Hajkowicz, L. A.


    The equatorial ionospheric response to 228 isolated, rapid-onset auroral substorms (as defined from the auroral electrojet index AE) was found from enhancements of the virtual (minimum) height of the F-region (h(') F) in the declining phase of a solar cycle (1980-85). The responses, found for three longitudinal sectors at the equator: Africa (Ouagadougou and Dakar), Asia (Manila) and America (Huancayo), were compared with the response close to the auroral source region at Yakutsk (northern Siberia). The auroral substorm onsets were centered at 17 and 15 UT at sunspot maximum (1980-82) and minimum (1983-85), preceding by 3-5 h the period of post-sunset height rise in the African sector whereas other sectors were in the early afternoon (Huancayo) and morning (Manila). The African response, particularly at Ouagadougou, was distinctly different from other sectors. In the sunspot maximum years (1980-81) the auroral surges were followed after about 3 h by a sharp depression (h(') Fh(') F=0) in 1982. A response polarity reversal (h(') F>0) was noted in this sector for sunspot minimum (1983-85) when large h(') F enhancements were observed at the sunset region. The responses in the Asian and American sector were positive except for a case in Huancayo when response was negative, following an auroral surge before the sunset at this station. It appears that the aurorally generated large-scale travelling ionospheric disturbances (LSTIDs), which first cause positive height enhancements in a sub-auroral location (Yakutsk), subsequently affect the unstable post-sunset ionosphere in the equatorial Africa.

  3. Equatorial ionospheric response to isolated auroral substorms over a solar cycle (1980−85: evidence of longitudinal anomaly

    L. A. Hajkowicz

    Full Text Available The equatorial ionospheric response to 228 isolated, rapid-onset auroral substorms (as defined from the auroral electrojet index AE was found from enhancements of the virtual (minimum height of the F-region (∆h$^prime$F in the declining phase of a solar cycle (1980–85. The responses, found for three longitudinal sectors at the equator: Africa (Ouagadougou and Dakar, Asia (Manila and America (Huancayo, were compared with the response close to the auroral source region at Yakutsk (northern Siberia. The auroral substorm onsets were centered at 17 and 15 UT at sunspot maximum (1980–82 and minimum (1983–85, preceding by 3–5 h the period of post-sunset height rise in the African sector whereas other sectors were in the early afternoon (Huancayo and morning (Manila. The African response, particularly at Ouagadougou, was distinctly different from other sectors. In the sunspot maximum years (1980–81 the auroral surges were followed after about 3 h by a sharp depression (∆h$^prime$F<0 in the post-sunset height rise, with a period of little or no response (∆h$^prime$F=0 in 1982. A response polarity reversal (∆h$^prime$F>0 was noted in this sector for sunspot minimum (1983–85 when large h$^prime$F enhancements were observed at the sunset region. The responses in the Asian and American sector were positive except for a case in Huancayo when response was negative, following an auroral surge before the sunset at this station. It appears that the aurorally generated large-scale travelling ionospheric disturbances (LSTIDs, which first cause positive height enhancements in a sub-auroral location (Yakutsk, subsequently affect the unstable post-sunset ionosphere in the equatorial Africa.

  4. On the triggering of auroral substorms by northward turnings of the interplanetary magnetic field

    J. A. Wild


    Full Text Available Some studies over the last decade have indicated that the instability responsible for substorm expansion phase onset may require an external trigger such as a northward turning of the interplanetary magnetic field (IMF. Statistical investigations have lead to contrasting interpretations regarding the relationship between proposed solar wind triggers and substorm onsets identified from geomagnetic data. We therefore present the results of a study into the possible triggering of 260 substorms between 2001–2005, exploiting data from the Cluster and IMAGE satellite missions. We find that only a small fraction (<25% of the substorms studied are associated with northward turnings of the IMF. However, the majority of the observed onsets are associated with a growth phase characterised using a subset of the criteria employed to define northward-turning IMF triggers. Based upon a case-by-case investigation and the results of an analysis using the statistics of point processes, we conclude that northward-turning structures in the IMF, while sometimes coinciding with the initial phase of individual substorms, are not required to trigger the magnetospheric instability associated with substorm expansion phase onset.

  5. Effect of auroral substorms on the ionospheric range spread-F enhancements at high southern midlatitudes using real time vertical-sounding ionograms

    Hajkowicz, Lech A.


    A comprehensive study has been undertaken on the effect of magnetic substorm onsets (as deduced from the auroral hourly electrojet AE-index) on the occurrence of high midlatitude (or sub-auroral latitude) ionospheric range spread-F (Sr). Unlike the previous reports real-time ionograms were used in this analysis thus eliminating ambiguities stemming from the correlating secondary evidence of spread-F with auroral substorms. The Australian southernmost ionosonde station Hobart (51.6°S geom.) proved to be uniquely suitable for the task as being sufficiently close to the southern auroral zone. Sr was assigned in km to each hourly nighttime ionogram at two sounding frequencies: Sr1 (at 2 MHz) and Sr2 (at 6 MHz) for four months in 2002: January and June (representing southern summer and winter solstices), and March and September (representing autumn and vernal equinoxes). It is evident that the southern winter solstitial period (June) is associated with high endemic midlatitude spread-F activity. All other seasons are closely linked with temporal sequences of enhanced spread-F activity following substorm onsets. For the first time it was possible not only find a simultaneous occurrence pattern of these diverse phenomena but to deduce numerical characteristics of the response of midlatitude ionosphere to the global auroral stimulus. Excellent case events, hitherto unpublished, are shown illustrating the presence of the AE peaks (in nT) being ahead of Sr peaks (in km) by a time shift ∆t (in h). Sr1 magnitude showed a significant correlation with the magnitudes of the preceding AE with a correlation coefficient (r) of 0.51 (probability of the occurrence by chance less than 0.01). Sr2 peaks were more sensitive to auroral disturbances but were not correlated with the AE magnitude variations. The time shift (∆t) was on average 4 h with a standard deviation of 3 h. The general pattern in the occurrence of magnetic substorms and spread-F is very similar. A number of

  6. The relationship between auroral hiss at high altitudes over the polar caps and the substorm dynamics of aurora

    Titova, E. E.; Yahnin, A. G.; Santolík, Ondřej; Gurnett, D. A.; Jiříček, František; Rauch, J. L.; Lefeuvre, F.; Frank, L. A.; Sigwarth, J. B.; Mogilevsky, M. M.


    Roč. 23, - (2005), s. 2117-2128. ISSN 0992-7689 R&D Projects: GA AV ČR IAA3042201; GA ČR GA205/03/0953; GA MŠk ME 650; GA ČR GA202/03/0832; GA MŠk 1P05ME811 Grant ostatní: ESA PECS(XE) 98025; INTAS(RU) 03-51-4132; NATO(XE) PST .GLG980041; NASA(US) NAG5-7943 Institutional research plan: CEZ:AV0Z30420517 Keywords : Magnetospheric physics (Auroral phenomena, Plasma waves and instabilities, Storms and substorms) Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.450, year: 2005

  7. On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations

    Motoba, T.; Ohtani, S.; Anderson, B. J.; Korth, H.; Mitchell, D. G.; Lanzerotti, L. J.; Shiokawa, K.; Connors, M. G.; Kletzing, C.; Reeves, G. D.


    Magnetotail processes and structures related to substorm growth phase/onset auroral arcs remain poorly understood mostly due to the lack of adequate observations. In this study we make a comparison between ground-based optical measurements of the premidnight growth phase/onset arcs at subauroral latitudes and magnetically conjugate measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) at ~780 km in altitude and by the Van Allen Probe-B spacecraft crossing L values of ~5.0-5.6 in the premidnight inner tail region. The conjugate observations offer a unique opportunity to examine the detailed features of the arc location relative to large-scale Birkeland currents and of the magnetospheric counterpart. The observations strongly suggest that the premidnight arc is connected to highly localized pressure gradients embedded in the near-tail R2 source region via a local upward FAC.

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

    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

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

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


    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...

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

    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)


    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

  11. Multiple-satellite studies of magnetospheric substorms: Plasma sheet recovery and the poleward leap of auroral-zone activity

    Particle observations from pairs of satellites (Ogo 5, Vela 4A and 5B, Imp 3) during the recovery of plasma sheet thickness late in substorms are examined. The time of occurrence and spatial extent of the recovery were related to the onset and approximate location of substorm expansions. It was found that the plasma sheet recovery occurred 10 - 30 min after the last in a series of Pi bursts, which indicates that the recovery is not due directly to a late, high-latitude substorm expansion. The recovery was also observed to occur after the substorm current wedge had moved into the evening sector and to extend far to the east of the center of the last preceding substorm expansion. During two events the plasma sheet in the near-earth tail was observed to recover within 1 - 2 min of the recovery in the Vela orbit. Recent magnetic field models suggest that the field lines through the spacecraft then intercepted the earth at high magnetic latitudes that are typically reached by ground activity during the 'poleward leap' late in a substorm. These concurrent plasma sheet recoveries, indicate that the recovery is due to a thickening of the plasma sheet toward higher latitudes that occurs over a broad azimuthal scale and from ionospheric heights to beyond the Vela orbit. The spatial character of these events is substantiated by an additional 20 correlated Ogo-Vela events. These results, are discussed in relation to current substorm models. This recovery appears to occur after the substorm expansion phase but before the beginning of the recovery phase; consequently, this phenomenon appears to represent a separate substorm phase. (JIW)

  12. VISIONS: Remote Observations of a Spatially-Structured Filamentary Source of Energetic Neutral Atoms near the Polar Cap Boundary During an Auroral Substorm

    Collier, Michael R.; Chornay, D.; Clemmons, J.; Keller, J. W.; Klenzing, J.; Kujawski, J.; McLain, J.; Pfaff, R.; Rowland, D.; Zettergren, M.


    We report initial results from the VISualizing Ion Outflow via Neutral atom imaging during a Substorm (VISIONS) rocket that flew through and near several regions of enhanced auroral activity and also sensed regions of ion outflow both remotely and directly. The observed neutral atom fluxes were largest at the lower energies and generally higher in the auroral zone than in the polar cap. In this paper, we focus on data from the latter half of the VISIONS trajectory when the rocket traversed the polar cap region. During this period, many of the energetic neutral atom spectra show a peak at 100 electronvolts. Spectra with peaks around 100 electronvolts are also observed in the Electrostatic Ion Analyzer (EIA) data consistent with these ions comprising the source population for the energetic neutral atoms. The EIA observations of this low energy population extend only over a few tens of kilometers. Furthermore, the directionality of the arriving energetic neutral atoms is consistent with either this spatially localized source of energetic ions extending from as low as about 300 kilometers up to above 600 kilometers or a larger source of energetic ions to the southwest.

  13. The convection electrojet and the substorm electrojet

    Y. Kamide

    Full Text Available Enhancements in the auroral electrojets associated with magnetospheric substorms result from those in either the electric field or the ionospheric conductivities, or both. Their relative importance varies significantly, even during a single substorm, depending on the location as well as on the substorm phases. It is predicted that different parts of the electrojets tend to respond in different ways to substorm activity. The unprecedented, unique opportunity for CLUSTER spacecraft observations of electric/magnetic fields and precipitating particles, combined with radar measurements of ionospheric quantities and with ground magnetometers, will provide us with crucial information regarding the physical nature of the separation between the "electric field-dominant'' and "conductivity-dominant'' auroral electrojets. This study also discusses the implications of these two auroral-electrojet components in terms of solar wind-magnetosphere-ionosphere interactions.

  14. Plasma sheet behavior during substorms

    Auroral or magnetic substorms are periods of enhanced auroral and geomagnetic activity lasting one to a few hours that signify increased dissipation of energy from the magnetosphere to the earth. Data acquired during the past decade from satellites in the near-earth sector of the magnetotail have suggested that during a substorm part of the plasma sheet is severed from earth by magnetic reconnection, forming a plasmoid, i.e., a body of plasma and closed magnetic loops, that flows out of the tail into the solar wind, thus returning plasma and energy that have earlier been accumulated from the solar wind. Very recently this picture has been dramatically confirmed by observations, with the ISEE 3 spacecraft in the magnetotail 220 R/sub E/ from earth, of plasmoids passing that location in clear delayed response to substorms. It now appears that plasmoid release is a fundamental process whereby the magnetosphere gives up excess stored energy and plasma, much like comets are seen to do, and that the phenomena of the substorm seen at earth are a by-product of that fundamental process

  15. Magnetospheric substorms

    The earth's magnetic tail acts as a reservoir for the energy that is extracted by the interaction between the solar wind and the earth's magnetosphere. Occasionally, a portion of that energy is released through a violent process known as a magnetospheric substorm. The substorm is one of the most important magnetospheric phenomena, and it is the subject of extensive research. Recent work utilizing data collected by the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer satellite, built at APL, has contributed markedly to the understanding of substorms. 11 refs

  16. Magnetospheric Substorm Electrodynamics

    Lyons, L. R.


    It was proposed that the expansion phase of substorms results from a reduction in the large-scale electric field imparted to the magnetosphere from the solar wind, following a greater than or equal to 30 min growth phase due to an enhancement in this electric field. The reduction in the electric field is assumed to propagate anti-sunward within the magnetosphere. Triggering by a reduction in the electric field is suggested by the observation that substorms are often triggered by northward turning of the interplanetary magnetic field (IMF). However, under the theory presented here, substorms may be triggered by anything that causes an electric field reduction such as a reduction in the magnitude of the y-component of the IMF. A reduction in the large-scale electric field disrupts both the inward motion and energization of plasma sheet particles that occurs during the growth phase. It is suggested here that this can lead to formation of the expansion-phase current wedge and active aurora. The current wedge results from the magnetic drift of ions, which has a speed proportional to particle energy, and a large azimuthal gradient in mean particle energy that is expected to develop in the vicinity of magnetic midnight during the growth phase. Current wedge formation will most likely be initiated near the radial distance (approx. 6- 10 R(sub E)) of the peak in the growth-phase plasma pressure distribution, and then propagate tailward from that region. Order-of-magnitude calculations show that the above proposal can account for the rapid development of the expansion phase relative to the growth phase, the magnitude of the reduction in the cross-tail current within the current wedge, the speeds of tailward and westward expansion of the current reduction region, the speeds of poleward and westward motion of active aurora in the ionosphere, and the magnitude of wedge field-aligned currents that connect the ionospheric region of active auroral to the divergent cross

  17. Coupling between pre-onset flows and substorm onset waves

    Nishimura, T.; Lyons, L. R.; Angelopoulos, V.; Donovan, E.; Mende, S. B.


    A critical, long-standing problem in substorm research is identification of the sequence of events leading to substorm expansion phase onset. Recent THEMIS all-sky imager (ASI) array observations have shown a repeatable pre-onset sequence, which is initiated by a poleward boundary intensification (PBI) and is followed by auroral streamers moving equatorward (earthward flow in the plasma sheet) and then by substorm onset. On the other hand, substorm onset is also preceded by azimuthally propagating waves, indicating a possible importance of wave instability for triggering substorm onset. However, it has been difficult to identify the link between fast flows and waves. We have found an isolated substorm event that was well-instrumented with the Poker Flat incoherent scatter radar (PFISR), THEMIS white-light ASI, and multi-spectral ASI, where the auroral onset occurred within the PFISR and ASI fields-of-view. This substorm onset was preceded by a PBI, and ionospheric flows propagated equatorward from the polar cap, crossed the PBI and reached the growth phase arc. This sequence provides evidence that flows from open magnetic field lines propagate across the open-closed boundary and reach the near-Earth plasma sheet prior to the onset. Quasi-stable oscillations in auroral luminosity and ionospheric density are found along the growth phase arc. These pre-onset auroral waves amplified abruptly at the onset time, soon after the equatorward flows reached the onset region. This sequence suggests a coupling process where pre-existing stable waves in the near-Earth plasma sheet interact with flows from further downtail and then evolve to onset instability.

  18. Substorm electrodynamics

    Stern, David P.


    The present one-dimensional model analysis of substorm electrodynamics proceeds from the standard scenario in which the plasma sheet collapses into a neutral sheet, and magnetic merging occurs between the two tail lobes; plasma flows into the neutral sheet from the lobes and the sides, undergoing acceleration in the dawn-dusk direction. The process is modified by the tendency of the accelerated plasma to unbalance charge neutrality, leading to an exchange of electrons with the ionosphere in order to maintain neutrality. The cross-tail current is weakened by the diversion: this reduces the adjacent lobe-field intensity, but without notable effects apart from a slight expansion of the tail boundary.

  19. Reconstruction of Fine Scale Auroral Dynamics

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


    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...

  20. Electrondynamics of the auroral E region

    This study concentrates on the signatures of the interaction process seen closest to the Earth - i.e. in the region where the visible aurora is produced. A number of experimental investigations are presented which look at details of the dynamics and electrodynamics of auroral ionisation features in the ionospheric E region. The studies are based primarily on measurement with the EISCAT UHF incoherent scatter radar which is located in northern Scandinavia. Initial calibration of the radar, and some measurements of the properties of the background atmosphere are described first. These are a necessary basis for the detailed studies which follow, which are of two aspects of auroral electrodynamics - substorms and aurorally-associated sporadic E layers. For the substorm studies, all-sky camera observations of the aurora over Scandinavia and ultra-violet images from the Viking satellite are used to identify the auroral forms corresponding to EISCAT measurements. This allows the determination of representative conductivities for the different auroral features which are characteristic of the substorm development. These conductivities are an important input for modelling studies of the electric current systems and have not previously been measured directly. Particle measurements from the Viking satellite are used together with EISCAT to determine the origin of the particles precipitated into the ionosphere during the energy-storage phase prior to the substorm. The sporadic E layers studies address the question of how ion layers and associated neutral sodium layers can be produced by some process which is common in association with auroral activity. Two candidates are considered - gravity waves and electric fields. (author)

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

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


    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.

  2. Hemispheric Assymeries in Auroral Precipitation

    Mende, S. B.


    It is widely accepted that the space weather related electrodynamic forcing of the geospace environment acts through the high geomagnetic latitude regions. At high latitudes inter-hemispheric asymmetries are largely due to the differences in solar illumination, the direction of the solar wind and interplanetary magnetic field components and to a lesser extent, due to differences between the two hemispheric internal fields. So far most research regarding interhemispheric differences concentrated on learning about the basic magnetosphere-ionosphere coupling mechanisms. It has been well established that sunlit conditions affect the energy flux of auroral precipitation resulting from the reduction in the mean energy of the auroral electrons in the sunlit summer hemisphere. This can be explained by the partial shorting out of the particle accelerating fields by the sunlight induced conductivity. It has also been found that sunlit conditions reduce the particle fluxes and therefore the associated field aligned currents. Unless the precipitation-induced conductivities overwhelm the sunlit component of conductivity, this would imply that the magnetospheric current generator responds to the ionospheric load in a highly non-linear manner. Interhemispheric currents may also play an important role that has not been fully explored. Interhemispheric asymmetries in substorm morphology have been explored critically because conjugacy implies that substorms have a common source at equatorial latitudes. In some cases the lack of conjugacy of substorms could be explained by considering the magnitude and direction of the IMF.

  3. Interplanetary energy flux associated with magnetospheric substorms

    It is shown that the interplanetary quantity epsilon(t), obtained by Perreault and Akasofu (Geophys. J.R. Astr. Soc.; 54: 547 (1978)) for intense geomagnetic storms, also correlates well with individual magnetospheric substorms. This quantity is given by epsilon(t)= VB2sin4 (theta/2) l02, where V and B denote the solar wind speed and the magnitude of the interplanetary magnetic field (IMF), respectively, and theta denotes the polar angle of the IMF; l0 is a constant approximately 7 Earth radii. The AE index is used in this correlation study. The correlation is good enough to predict both the occurrence and intensity of magnetospheric substorms observed in the auroral zone, by monitoring the quantity epsilon(T) upstream of the solar wind. (author)

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

    Dods, J; Gjerloev, J W


    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...

  5. Evolution of high latitude ionospheric convection associated with substorms: Multiple radar observations

    Zou, Shasha

    The work presented in this dissertation concerns evolution of the high latitude ionospheric convection and the relevant current systems associated with substorms, with emphasize on these features near the nightside Harang reversal region. Three different types of radars, including the Super Dual Auroral Radar Network (SuperDARN) coherent-scatter radars, the new advanced modular incoherent-scatter radar at Poker Flat (PFISR), and the Sondrestrom incoherent-scatter radar (ISR), have been utilized. Observations from those radars, together with those from complementary instruments, including satellites and other ground-based instruments, have revealed fundamental new understand of the ionospheric electrodynamic properties associated with substorms. By using the SuperDARN and the PFISR radars, we found that the auroral activity at substorm onset is located in the center of the Harang reversal, which represents a key region in the magnetospheric and ionospheric convection and is part of the Region 2 system. We have also shown that nightside convection flows exhibit repeatable, distinct variations at different locations relative to the substorm-related auroral activity. Taking advantage of the simultaneous flow and ionization measurements from PFISR, a current closure relation has been found between the Region 2 and the substorm field-aligned current systems. These observations demonstrate a strong coupling between the Region 2 system and the substorm dynamics. This study sheds new light on the substorm-related magnetosphere-ionosphere coupling and contributes to the building of a holistic picture of the substorm dynamics. The third radar has been used to study the dayside ionospheric convection response to the external soar wind and IMF driving and its role in substorm dynamics. The results have been applied to study substorm triggering and in the future could be used to study the relation between the external driving and the formation of the Harang reversal.

  6. 2-D Convection and Electrodynamic Features of Substorms Revealed by Multiple Radar Observations (Invited)

    Zou, S.


    Substorms are one of the fundamental elements of geomagnetic activity, which involve complex magnetosphere-ionosphere coupling processes. In this work, we aim to better understand the evolution of high latitude ionospheric convection and the relevant current systems associated with substorms, with emphasis on these features near the nightside Harang reversal region. Three different types of radars, including the Super Dual Auroral Radar Network (SuperDARN) coherent-scatter radars, the new advanced modular incoherent-scatter radar at Poker Flat (PFISR), and the Sondrestrom ISR, have been utilized. Observations from these radars, together with those from complementary instruments, including satellites and other ground-based instruments, have enabled fundamental new understanding of the ionospheric electrodynamic properties associated with substorms. In this presentation, I focus on electrodynamics near the nightside Harang reversal region. Observations from the SuperDARN and the PFISR radars revealed that auroral activity at substorm onset is located near the center of the Harang reversal, which represents a key feature of magnetospheric and ionospheric convection and is part of the Region 2 system. The observations also show nightside convection flows exhibit repeatable, distinct variations at different locations relative to the substorm-related auroral activity. Taking advantage of the simultaneous flow and ionization measurements from PFISR, a current closure relation has been found between the Region 2 and the substorm field-aligned current systems. By synthesizing these observations, a 2-D comprehensive view of the nightside ionospheric electrodynamical features, including electrical equipotentials, flows and FACs, and their evolution associated with substorms has been constructed, which has revealed a strong coupling between the substorm and the Region 2 current systems. This study sheds new light on substorm-related magnetosphere-ionosphere coupling and

  7. Associations of IMF polarity, plasma sheet thinning, and substorm occurrence on March 6, 1970

    Two substorms on March 6, 1970, were observed by the Vela 5A satellite in the magnetotail plasma sheet and by all-sky cameras along the Alaska meridian. The first substorm started early in a 3-hour interval of southward polarity of the interplanetary magnetic field (IMF). The second substorm, which was much more intense than the first and whose beginning was particularly well marked by the classical auroral and magnetic signatures of an expansive phase onset, started near the end of the 3-hour interval as the IMF was becoming less southward. Only sporadic and partial thinning of the plasma sheet was observed during the first substorm, whereas very rapid and extreme thinning of the plasma sheet occurred within minutes after the onset time of the second, more intense substorm. The observations during these two substorms thus do not fit in a straightforward way a theoretical framework which holds that the southward turning of the IMF leads to plasma sheet thinning and then to the substorm onset unless such thinning is localized in azimuth or in radial distance. An observed correlation of the sporadic partial thinnings during the first substorm with passage of westward traveling surges through the evening sector of the auroral oval suggests that surges may be magnetic projections, to the earth, of westward propagating 'waves' in the radial distance to a magnetic neutral line. The peak-to-peak amplitude of the waves may be as great as 5--10 earth radii

  8. 12-hour case study of auroral phenomena in the midnight sector: Electrojet and precipitating particle characteristics

    Airborne observations of auroral activity at midnight were conducted for a period of 9 hours by employing an ionospheric sounder and all-sky cameras. During the observation period, two substorms occurred. The first substorm was assciated with a compression of the magnetosphere (as measured by Dst) and with oscillations of the earth's bow shock. At this time, auroral activity was characterized by a series of poleward and equatorward motions and by the absence of a breakup phase. Magnetic disturbances were confined to a small region in the midnight sector. The second auroral substorm displayed many of the features assocated with a large-scale polar magnetic substorm. For selected times the locations of the eastward and westward electrojets were inferred from a number of high-latitude magnetic records. All-sky photographs and ionosonde data indicate that the poleward edge of the westward electrojet was bounded by a westward moving auroral surge accompanied by a strong sporadic E ionization. The equatorward electrojet boundary was less well defined by visual auroral forms. Soft particle spectrometer measurements from the Isis 2 satellite were made in conjunction with the aircraft measurements and indicate that large fluxes of field-aligned electrons gave rise to the bright auroral surge, more isotropic fluxes of less energetic electrons contributing to the auroral E layer

  9. Substorm triggering by poleward boundary intensification and related equatorward propagation

    Mende, S. B.; Frey, H. U.; Angelopoulos, V.; Nishimura, Y.


    Recently, a revised auroral substorm onset sequence has been proposed, in which onset is preceded by a poleward boundary intensification (PBI) and subsequent equatorward propagation of N-S-aligned auroral features to breakup arc latitudes. We reanalyzed 20 randomly selected samples of the Nishimura et al. (2010) 251-event database and show in greater detail to what degree the observed features in this subset of events are consistent with the proposed scenario. To assess the sensitivity of space-based imagers for seeing this scenario, we calibrated the absolute responsivity of the THEMIS ground-based imagers. We also show that although not suitable for studies from apogee, IMAGE/FUV imagers can also observe a consistent scenario from a lower altitude. We conclude that in some cases PBIs and subsequent plasma flows can be effective in providing a trigger if the inner magnetosphere is ready to produce a substorm.

  10. Substorm aurora and magnetic tail dynamics during interplanetary shock compression: THEMIS observations

    Angelopoulos, Vassilis; Zhou, Xiaoyan


    Fast and forward interplanetary shocks compress and squeeze the Earth magnetosphere and cause a series of magnetospheric and ionospheric reactions. In addition to the enhancement of chorus, electromagnetic ion cyclotron (EMIC) waves and magnetospheric hiss, the ionospheric convection is enhanced as well. Shock aurora is generated, which is a phenomenon first an auroral brightness onset near local noon right after the shock impingement then followed by a fast anti-sunward auroral propagation along the oval. It has been found that substorm auroral activity can be significantly intensified by the shock compression when the shock upstream magnetic field was in southward in a certain period of time. This paper will present recent results based on the THEMIS spacecraft and ground-based observations. With multiple spacecraft in the magnetotail, the complex dynamics of the compressed tail is identified and analyzed. Correlations between the tail dynamics and substorm auroral variations will be discussed. *On-leave from Jet Propulsion Laboratory

  11. Ground and satellite observations of auroral fragmentation into patches

    Shiokawa, Kazuo; Nishi, Katsuki


    We review characteristic auroral fragmentation which is the process by which uniform aurora is broken into several fragments to form auroral patches, based on the all-sky camera observations at Tromsoe, Norway and THEMIS chain in Canada. The auroral fragmentation occurs as finger-like structures developing predominantly in meridional direction with speeds of several tens m/s and scale sizes of several tens kilometers without any shearing motion. These features suggest that pressure-driven instability in the balance between the earthward magnetic-tension force and the tailward pressure gradient force in the magnetosphere is the main driving force of the auroral fragmentation. Thus, these observations indicate that auroral fragmentation associated with pressure-driven instability is a process that creates auroral patches. Auroral fragmentation is seen from midnight to dawn local time and usually appears at the beginning of the substorm recovery phase, near the low latitude boundary of the auroral region. One example of plasma and magnetic field observations by the THEMIS satellite in the conjugate magnetosphere shows diamagnetic anti-phase variations of magnetic and plasma pressures with time scales of several to tens minutes associated with the auroral fragmentation. This observation also supports the idea of pressure-driven instability to cause the auroral fragmentation into patches.

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

    Henderson, Michael G [Los Alamos National Laboratory


    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.

  13. Superposed epoch analysis of the ionospheric convection evolution during substorms: onset latitude dependence

    A. Grocott


    Full Text Available Using data from the Super Dual Auroral Radar Network (SuperDARN we investigate the ionospheric convection response to magnetospheric substorms. Substorms were identified using the Far Ultraviolet (FUV instrument on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE spacecraft, and were then binned according to the magnetic latitude of their onset. A superposed epoch analysis of the ionospheric convection patterns for each onset-latitude bin was then performed using radar data for the interval 60 min before onset to 90 min after. It is found that lower onset-latitude substorms are associated with generally more enhanced convection than the higher latitude substorms, although they suffer from a significant localised reduction of the flow in the midnight sector during the expansion phase. Higher-latitude substorms are associated with a significant and rapid increase in the nightside convection following substorm onset, with all onset-latitude bins showing an enhancement over onset values by ~60 min into the expansion phase. A rudimentary inspection of the concurrent auroral evolution suggests that the duration of the flow reduction following substorm onset is dependent on the strength and duration of the expansion phase aurora and its associated conductivity enhancement.

  14. A missing variable in the data-based substorm studies

    Sergeev, Viktor; Angelopoulos, Vassilis; Sormakov, Dmitry

    Nowadays the quantitative characterization of the magnetospheric activity is predominantly based on the amplitude of auroral zone magnetic perturbations (e.g., AL index value). This approach ignores the long-established fact that ground magnetic perturbations are basically formed by the Hall currents (Fukushima theorem), which depend critically on the Hall conductivity and, therefore, are sensitive to the plasma sheet electron parameters (Te and Ne, which also control the production of energetic electrons by their field-aligned acceleration). Observational confirmation of such influence is difficult because of many complicating factors, main of which are the inhomogeneity of Te, Ne parameters in the magnetotail and, especially, the reconnection-induced production of low-density and high-temperature electrons during substorms in the magnetotail. In this study, based on long-term monitoring of plasma sheet electrons by THEMIS spacecraft, we (a) demonstrate a strong variation of auroral zone currents (by an order of magnitude depending on the plasma sheet Te/Ne value) under the conditions of the substorm growth phase (when substorm-related acceleration is weak), (b) compare the average behaviors of Te, Ne during substorms under very large (very small) Te/Ne conditions and (c) briefly discuss a number of ’phantom problems’ which arise due to the ignorance of this dependence (incl. the problem of pseudobreakups, etc).

  15. Investigations of auroral dynamics: techniques and results

    This study is an experimental investigation of the dynamics of the aurora, describing both the systems developed for the optical measurements and the results obtained. It is found that during a auroral arc deformation, a fold travelling eastward along the arc is associated with an enhanced F-region ion temperature of 2700 K, measured by EISCAT, indicative of enhanced ionspheric electric fields. It is shown that for an auroral break-up, the large-scale westward travelling surge (WTS) is the last developed spiral in a sequence of spiral formations. It is proposed that the Kelvin-Helmholtz instability is the responsible process. In another event it is shown that large-amplitude long-lasting pulsations, observed both in ground-based magnetic field and photometer recordings, correspond to strong modulations of the particle intensity at the equatorial orbit (6.6 Re). In this event a gradual transition occurs between pulses classified as Ps6/auroral torches toward pulses with characteristics of substorms. The observations are explained by the Kelvin-Helmholtz instability in a magnetospheric boundary layer. The meridional neutral wind, at about 240 km altitude, is found to be reduced prior to or at the onset of auroral activity. These findings are suggestive of large-scale reconfigurations of the ionspheric electric fields prior to auroral onsets. A new real time triangulation technique developed to determine the altitude of auroral arcs is presented, and an alternative method to analyze incoherent scatter data is discussed. (With 46 refs.) (author)

  16. Observation of auroral fading before breakup

    We have obtained detailed observations of the onset of auroral breakup using a variety of instruments with time resolution of some tens of seconds. Rapid sequences of all-sky photographs, and fast meridian scans by photometers, show that breakup is usually preceded by moderate brightening, followed by fading of the auroral brightness lasting one or two minutes, before the actual breakup itself. At the time of the fading there is a brief darkening of the poleward sky. Often the breakup is preceded by one or more rapid intensifications, each one preceded by local fading. Pseudo-breakups may also occur without the development of a major event. A bonafide breakup may begin on the fading arc, on an adjacent arc, or in an entirely new region nearby. This optical activity is closely correlated with the development of auroral radar echoes, suggesting that variations in the ionospheric and magnetospheric electric and magnetic fields are responsible for the observed auroral variations. Data from the IMS magnetometer network provide some indication of a correlated response by the local auroral and ionospheric current, although this could be partly due to changes in conductivity. Riometer recordings show a slow decrease in ionsperic radio wave absorption over a period of about ten minutes prior to breakup, with the largest decrease essentially to quiet-time values in the region of auroral fading and subsequent breakup. The implications of these observations regarding the trigger mechanism for the expansion phase of a magnetospheric substorm are discussed. (author)

  17. Multipoint observations of a small substorm

    In this paper the authors present multipoint observations of a small substorm which occurred just after 0110 UT on April 25, 1985. The observations were made by spacecraft (AMPTE CCE, AMPTE IRM, DMSP F6, and DMSP F7), ground auroral stations (EISCAT magnetometer cross, Syowa, Narssarssuaq, Great Whale River, and Fort Churchill), and mid-latitude stations (Furstenfeldbruck, Toledo, and Argentine Island). These data provide them with a broad range of observations, including the latitudinal extent of the polar cap, visual identification of substorm aurorae and the magnetic perturbations produced directly beneath them, in situ magnetic field and energetic particle observations of the disruption of the cross-tail current sheet, and observations concerning the spatial expansion of the current disruption region from two radially aligned spacecraft. The DMSP data indicate that the event took place during a period when the polar cap was relatively contracted, yet the disruption of the current sheet was observed by CCE at 8.56 RE. They have been able to infer a considerable amount of detail concerning the structure and westward expansion of the auroral features associated with the event, and they show that those auroral surges were located more than 10 degree equatorward of the boundary between open and closed field lines. Moreover, they present evidence that the current sheet disruption observed by CCE in the neutral sheet was located on field lines which mapped to the westward traveling surge observed directly overhead of the ground station at Syowa. Furthermore, the observations strongly imply that disruption of the cross-tail current began in the near-Earth region and that it had a component of expansion which was radially antisunward

  18. The dawn and dusk electrojet response to substorm onset

    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

  19. A magnetospheric substorm observed at Sanae, Antarctica

    A magnetospheric substorm that occurred at Sanae, Antarctica, on July 27, 1979, was observed by a variety of techniques. A synthesis of the observations is presented, and an attempt made to deduce details of the behavior of the magnetosphere-ionosphere system during the event. While there was some evidence of a growth phase, it was inconclusive. At the onset there was a rapid change in the tail field, which assumed a more dipolar form, accompanied by Pi 2 oscillations and the precipitation of 6-keV electrons, with brightening of the auroral arc, auroral-type sporadic E ionization, and riometer absorption. A positive spike was observed in the D magnetic component, instead of the expected negative one. There was no evidence of the usual westward traveling surge at the beginning of the expansion phase during which the precipitation region, auroral arc, and electrojet moved rapidly poleward, though it may have occurred outside the field of view from Sanae. The Hβ emission increased by a factor of less than 2, whereas the oxygen and nitrogen emissions monitored increased by 3-4. During the recovery phase, phenomena were consistent with a return of the tail field to an elongated form; a very high ratio of 557.7-nm/630-nm emissions, exceeding 10, was observed; and the electrojet lagged noticeably behind the photon emission regions

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

    Fox, N.J.; Cowley, S.W.H.; Davda, V.N.; Enno, G.; Friis-Christensen, Eigil; Greenwald, R.A.; Hairston, M.R.; Lester, M.; Lockwood, M.; Luhr, H.; Milling, D.K.; Murphree, J.S.; Pinnock, M.; Reeves, G.D.


    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. The...

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

    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

  2. Electron precipitation morphology and plasma sheet dynamics: ground and magnetotail studies of the magnetospheric substorm

    The main results of some recent studies of the magnetospheric substorm are summarised and discussed in view of the fundamental role of magnetospheric convection. The substorm growth phase is described in terms of a temporary imbalance between the rates of magnetic field-line merging on the dayside, and reconnection on the nightside, of the magnetosphere following a southward turning of the interplanetary magnetic field. Some new understanding of the possible causal relationship between growth-phase and expansion-phase phenomena is provided through studies of multiple-onset substorms, during which substorm expansions are observed to occur at intervals of 10-15 min. Detailed observations have revealed new features of the radial and azimuthal dynamics of these substorms that are not consistent with recent models proposed by Akasofu and by Rostoker and his co-workers. It is shown that the behaviour of the near-earth plasma sheet early in a substorm cannot be inferred from measurements at larger distances (e.g., in the Vela satellite orbits), and that the triggering of a substorm expansion may well be directly related to pre-substorm thinning of the near-earth plasma sheet, even though the most significant thinning in the tailward region may occur at the onset, and therefore appears to be an effect rather than a cause of triggering. Initial results from studies of a new type of magnetospheric activity, characterised by strong auroral-zone bay activity but no other indications of substorm expansions, are shown to be consistent with current models of the growth and expansion phases of substorms and of substorm triggering. (JIW)

  3. Spatial scaling of optical fluctuations during substorm-time aurora

    B. V. Kozelov


    Full Text Available A study of statistical features of auroras during substorm activity is presented, emphasizing characteristics which are commonly applied to turbulent flows. Data from all-sky television (TV observations from the Barentsburg observatory (Svalbard have been used. Features of the probability density function (PDF of auroral fluctuations have been examined at different spatial scales. We find that the observed PDFs generally have a non-Gaussian, heavy-tailed shape. The generalized structure function (GSF for the auroral luminosity fluctuations has been analyzed to determine the scaling properties of the higher (up to 6 order moments, and the evolution of the scaling indices during the actual substorm event has been determined. The scaling features obtained can be interpreted as signatures of turbulent motion of the magnetosphere-ionosphere plasma. Relations to previously obtained results of avalanche analysis of the same event, as well as possible implications for the validity of self-organized criticality models and turbulence models of the substorm activity, are discussed.

  4. Global properties of the magnetosphere during a substorm growth phase: A case study

    At approximately 0100 UT on December 29, 1976, a large injection of energetic (>30 keV) particles was observed by Los Alamos instrumentation onboard spacecraft 1976--059 (35 0W longitude) at geostationary orbit. This injection was closely associated with the onset of a major substorm (also at 0100 UT) identified by sharp negative bays in the H components of magnetic records at Leirvogur (22 0W) and Narssarssuaq (45 0W) and by the occurrence of a positive H component bay at 0100 UT in the mid-latitude magnetogram record at M'Bour (17 0W). This substorm expansion onset (and concomitant particle injection) was preceded (between 2330 and 0100 UT) by a pronounced 'stretching' of the magnetic field at synchronous orbit into a taillike configuration and by a development of highly cigarlike (field-aligned) electron distributions at geostationary orbit that we have in the past identified with the substorm growth phase. Of principal importance in this case are two other auxiliary data sets. The first is a well-timed set of DMSP auroral images taken during the course of the growth and expansion phases of the substorm. The images before and during the growth (cigar) phase, including one auroral zone crossing at approx.0050 UT, show quiet aurora with no observable substorm activity in the visible polar region. The second relevant data set is a broad set of riometer data from 13 separate stations in three general meridians (west coast Greenland, east coast Greenland, and northern Scandinavia) from magnetic latitudes of approx.650 to approx.900. The riometer data also show clearly that there was no measurable substorm activity anywhere, either in longitude or latitude, as the magnetosphere developed its very stressed, growth-phase configuration prior to substorm expansion onset. These results support the concept of a storage of energy (growth phase) prior to its rapid release at substorm onset

  5. Substorms on Mercury

    The Mariner 10 encounter of Mercury provided data showing a strong interaction between the solar wind and the planet similar to a scaled down version of that producing the earth's magnetosphere. Some of the features observed in Mercury's night side magnetosphere suggest time-dependent processes occurring there. Interpreted as temporal events, these features bear striking resemblances to substorm phenomena in the earth's magnetosphere

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

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


    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...

  7. Experimental study of diffuse auroral precipitations

    First chapter is devoted to low energy electron precipitation in the evening sector of the auroral magnetosphere, during quiet and disturbed magnetic periods. Four subjects are studied in detail: the latitude distribution of the varied auroral forms and their relations to external magnetosphere; the time coefficients related to precipitations, the form and the dynamic of the diffuse precipitation equatorial frontier; the precipitation effect on the ionosphere concentration. The last part of the chapter shows that the plasma convection in the magnetosphere, associated to wave-particle interactions near the equatorial accounts for the principal characteristics of the evening sector diffuse electronic precipitations. The second chapter deals with subauroral precipitations of low energy ions, after the magnetospheric substorms, in the high latitude regions of the morning sector

  8. Propagation of BBFs and Dipolarization Fronts in the Global MHD simulation of February 27, 2009 Substorm

    Ge, Y.; Raeder, J.; Angelopoulos, V.; Gilson, M. L.; Runov, A.


    A global MHD simulation has been performed to investigate the THEMIS substorm on February 27, 2009. During this substorm the conjugated observations from the space and on the THEMIS ground observatories are available. The location and time of this substorm onset can be determined based on these observations. The initial auroral brightening is found at around 07:49 UT in the field of view of Fort Smith station (FSMI), with a pre-existing auroral arc located equatorward. A couple minutes later, the in situ observations recorded a sharp dipolarization front sunward passing through THEMIS spacecraft, which travels almost 10 RE in the magnetotail. In this study our global MHD model, i.e., OpenGGCM, driven by the real-time solar wind/IMF conditions, is able to reproduce the key features of these substorm signatures, including the auroral breakup at FSMI with the same onset time as the observations, and a strong earthward Bursty Bulk Flow (BBF) and dipolarization fronts that cause the substorm onset signatures. It is found in the simulation that the auroral breakup is caused by the strong flow shear and the flow vortices which form as the BBF moves earthward. Investigation of the tail BBF and its dipolarization front (DF) reveals that the bipolar change of the Bz component ahead of the DF can be produced by the interaction between two distinct plasmas from separate X lines: the anti-sunward moving southward flux tubes in the tailward flows emanating from an inner magnetic reconnection region, and the sunward traveling dipolarized tubes within the front of a strong earthward BBF that originates in a mid-tail reconnection region. The rebound and oscillations of the intruding BBF reported by the recent THEMIS observations are also seen in the simulation when the BBF encounters the high-pressure inner magnetosphere.

  9. Particle simulation of auroral double layers. Doctoral thesis

    Smith, B.L.


    Externally driven magnetic reconnection has been proposed as a possible mechanism for production of auroral electrons during magnetic substorms. Fluid simulations of magnetic reconnection lead to strong plasma flows towards the increasing magnetic field of the earth. These plasma flows must generate large scale potential drops to preserve global charge neutrality. We have examined currentless injection of plasma along a dipole magnetic field into a bounded region using both analytic techniques and particle simulation.

  10. A modeling of magnetic field variations during magnetospheric substorms

    Akasofu, S.-I.; Corrick, G. K.


    Magnetic field variations in the noon-midnight plane during the magnetospheric substorm are studied in terms of changes of three current systems: the dynamo-driven current on the magnetopause, the cross-tail current and the field-aligned current-auroral electrojet system. The field-aligned current is assumed to be generated as a result of interruption and subsequent diversion of the cross-tail current to the ionosphere. It is concluded that the available observations are consistent with a large increase of the three currents.

  11. Role of ionospheric effects and plasma sheet dynamics in the formation of auroral arcs

    Prakash, Manju; Rankin, R.


    At the ionospheric level, the substorm onset (expansion phase) is marked by the initial brightening and subsequent breakup of a pre-existing auroral arc. According to the field line resonance (FLR) wave model, the substorm-related auroral arc is caused by the field-aligned current carried by FLRs. The FLRs are standing shear Alfvén wave structures that are excited along the dipole/quasi-dipole lines of the geomagnetic field. The FLRs (that can cause auroral arc) thread from the Earthward edge of the plasma sheet and link the auroral arc to the plasma sheet region of 6-15 R_E. The region is associated with magnetic fluctuations that result from the nonlinear wave-wave interactions of the cross-field current-instability. The instability (excited at the substorm onset) disrupts the cross-tail current which is built up during the growth phase of the substorms and results in magnetic fluctuations. The diversion of the current to polar regions can lead to auroral arc intensification. The current FLR model is based on the amplitude equations that describe the nonlinear space-time evolution of FLRs in the presence of ponderomotive forces exerted by large amplitude FLRs (excited during substorms). The present work will modify the FLR wave model to include the effects arising from magnetic fluctuations that result from current disruption near the plasma sheet (6-15 R_E). The nonlinear evolution of FLRs is coupled with the dynamics of plasma sheet through a momentum exchange term (resulting from magnetic fluctuations due to current disruption) in the generalized Ohm's law. The resulting amplitude equations including the effects arising from magnetic fluctuations can be used to study the structure of the auroral arcs formed during substorms. We have also studied the role of feedback mechanism (in a dipole geometry of the geomagnetic field) in the formation of the discrete auroral arc observed on the nightside magnetosphere. The present nonlinear dispersive model (NDM) is

  12. Interplanetary Alfven waves and auroral (substorm) activity: IMP 8

    Almost year of IMP 8 interplanetary magnetic field and plasma data (Days 1-312, 1979) have been examined to determine the interplanetary causes of geomagnetic AE activity. The nature of the interplanetary medium (Alfvenic or non-Alfvenic) and the B2 correlation with AE were examined over 12-hour increments throughout the study. It is found that Alfvenic wave intervals (defined as Vx-Bx cross-correlation coefficients of >0.6) are present over 60% of the time and the southward component of the Alfven waves is well correlated with AE (average peak correlation coefficient 0.62), with a median lag of 43 min. The most probable delay of AE from Bs is considerably shorter, about 20-25 min. Southward magnetic fields during non-Alfvenic intervals (Vx-Bx cross-correlation coefficients of s were variable from event to event (and at different times within the Alfven wave train), ranging from 45 min to as little as 0 min. The cause of this variable delay is somewhat surprising and is not presently well understood

  13. Auroral electrojets during severely disturbed geomagnetic condition on 24 August 2005

    Singh, Anand K.; Sinha, A. K.; Saini, S.; Rawat, Rahul


    Very intense and highly dynamic eastward and westward currents flowing in the auroral ionosphere are traditionally monitored by the auroral electrojet indices - AUand AL , respectively. In this study we show that on occasions of intense magnetic activity, entire auroral oval could be dominated by the westward flowing currents, which lead to depression not only in AL index but also in supposedly positive AU index. During negative AU intervals, there could be up to ∼ 20 % underestimation of the total maximum intensity of the auroral electrojet represented by AEindex (defined as AU - AL). A detailed investigation of a well-studied extremely intense event of 24 August 2005 has been carried out. Global prevalence of the westward auroral electrojet was clearly observed at the auroral latitudes during the unusually intense substorm (AL ∼ - 4000 nT) on the day. Moreover, along the noon meridian westward electrojet appeared in the auroral region whereas eastward electrojet shifted towards lower latitudes. This paper emphasizes that intense substorms are represented better by AL index than AE index.

  14. About the relationship between auroral electrojets and ring currents

    A. Grafe

    Full Text Available The relationship between the storm-time ring current and the auroral electrojets is investigated using IMAGE magnetometer data, DSt and H-SYM, and solar wind data. Statistical results as well as the investigation of single events show that the auroral electrojets occur also during nonstorm conditions without storm-time ring current development and even during the storm recovery phase of increasing DSt. A close correlation between electrojet intensity and ring current intensity was not found. Though the eastward electrojet moves equatorward during the storm main phase there is no unequivocal relationship between the movement of the westward electrojet and the ring current development. All these results suggest that the auroral electrojets and the ring current develop more or less independently of each other.

    Key words: Magnetospheric physics (magnetosphere-ionosphere interactions; storms and substorms

  15. Reconnection in substorms

    Schindler, K.

    This paper attempts to deal with magnetospheric activity from the kinematic point of view, using the homogeneous subset of Maxwell's equations and Ohm's law. This approach gives insight into three major substorm processes: Plasma entry through the magnetopause (including impulsive penetration), plasmoid formation in the magnetotail and near-Earth magnetic reconfiguration. The central quantity is a generalized electric potential arising from electric field components parallel to the magnetic field. The present discussion is also extended to solar activity and to deviations from isorotation with possible consequences for the origin of cosmic rays.

  16. Cluster observation of plasma flow reversal in the magnetotail during a substorm

    A. T. Y. Lui; Zheng, Y; Zhang, Y.; Livi, S; H. Rème; M. W. Dunlop; G. Gustafsson; Mende, S. B.; Mouikis, C.; Kistler, L. M.


    We investigate in detail a reversal of plasma flow from tailward to earthward detected by Cluster at the downstream distance of ~19 RE in the midnight sector of the magnetotail on 22 August 2001. This flow reversal was accompanied by a sign reversal of the Bz component and occurred during the late substorm expansion phase as revealed by simultaneous global view of auroral activity from IMAGE. We exami...

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

    Winglee, Robert


    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...

  18. Forecast of auroral activity

    A new technique is developed to predict auroral activity based on a sample of over 9000 auroral sites identified in global auroral images obtained by an ultraviolet imager on the NASA Polar satellite during a 6-month period. Four attributes of auroral activity sites are utilized in forecasting, namely, the area, the power, and the rates of change in area and power. This new technique is quite accurate, as indicated by the high true skill scores for forecasting three different levels of auroral dissipation during the activity lifetime. The corresponding advanced warning time ranges from 22 to 79 min from low to high dissipation levels

  19. Instantaneous ionospheric global conductance maps during an isolated substorm

    A. Aksnes

    electron energy range is more or less comparable with the energy ranges of the statistical models. By calculating the conductivities from combined PIXIE and UVI measurements to compare with the conductivities from using UVI data only, we observe significant differences in the Hall conductance. The greatest differences are observed in the early evening and the late morning sector. We therefore suggest that the existing statistical models underestimate the Hall conductance.

    Key words. Ionosphere (auroral ionosphere, particle precipitation – Magnetospheric physics (storms and substorms

  20. Auroral boundary dynamics observed simultaneously from the Viking spacecraft and from the ground

    High spatial and temporal resolution auroral imaging from space and from the ground contiues to improve our understanding of auroral dynamics. The ultraviolet imager on the Viking spacecraft gives global information on the activity of the auroral distribution. The ground-based optical facility at Swedish Institute of Space Physics, in Kiruna, Sweden, gives information on the finer-scale auroral structure. Simultaneous satellite- and ground-based measurements using this instrumentation were obtained for three selected events during the spring of 1986. For some aspects the authors find a remarkable correspondence of particular features observed from space and from the ground. For others the different views are complementary in nature. Taken together, they provide a comprehensive picture of presubstorm, substorm, and postsubstorm dynamics. The major findings are (1) a narrow active rayed arc set within a background of softer precipitation that defines what is generally called the diffuse aurora, with repeated fading on the time scale of 5 min; (2) a period of rapid convection manifested by the disappearance of transpolar arcs and the onset of undulations of the poleward boundary arc observed well before substorm onset; and (3) two clearly separated latitudinal regions following substorm onset, the poleward one being more variable on a time scale of 10 min, but the equatorward one having at its equatorward boundary a coherent pulsating feature with periods in the range 1-3 min

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

    A small, isolated substorm with an expansion phase onset at 07:39 U.T. (±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 (∼220 RE) 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)

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

    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

  3. Stochastic modeling of the auroral electrojet index

    Anh, V. V.; Yong, J. M.; Yu, Z. G.


    Substorms are often identified by bursts of activities in the magnetosphere-ionosphere system characterized by the auroral electrojet (AE) index. The highly complex nature of substorm-related bursts suggests that a stochastic approach would be needed. Stochastic models including fractional Brownian motion, linear fractional stable motion, Fokker-Planck equation and Itô-type stochastic differential equation have been suggested to model the AE index. This paper provides a stochastic model for the AE in the form of fractional stochastic differential equation. The long memory of the AE time series is represented by a fractional derivative, while its bursty behavior is modeled by a Lévy noise with inverse Gaussian marginal distribution. The equation has the form of the classical Stokes-Boussinesq-Basset equation of motion for a spherical particle in a fluid with retarded viscosity. Parameter estimation and approximation schemes are detailed for the simulation of the equation. The fractional order of the equation conforms with the previous finding that the fluctuations of the magnetosphere-ionosphere system as seen in the AE reflect the fluctuations in the solar wind: they both possess the same extent of long-range dependence. The introduction of a fractional derivative term into the equation to capture the extent of long-range dependence together with an inverse Gaussian noise input describe the right amount of intermittency inherent in the AE data.

  4. Substorms - Future of magnetospheric substorm-storm research

    Seven approaches and/or areas of magnetospheric substorm and storm science which should be emphasized in future research are briefly discussed. They are: the combining of groups of researchers who study magnetic storms and substorms in terms of magnetic reconnection with those that do not, the possible use of a magnetosphere-ionosphere coupling model to merge the groups, the development of improved input-output relationships, the complementing of satellite and ground-based observations, the need for global imaging of the magnetosphere, the complementing of observations with computer simulations, and the need to study the causes of changes in the north-south component of the IMF. 36 refs

  5. Threshold of auroral intensification reduced by electron precipitation effect

    Hiraki, Yasutaka


    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.

  6. The equatorial electrojet during geomagnetic storms and substorms

    Yamazaki, Yosuke; Kosch, Michael J.


    The climatology of the equatorial electrojet during periods of enhanced geomagnetic activity is examined using long-term records of ground-based magnetometers in the Indian and Peruvian regions. Equatorial electrojet perturbations due to geomagnetic storms and substorms are evaluated using the disturbance storm time (Dst) index and auroral electrojet (AE) index, respectively. The response of the equatorial electrojet to rapid changes in the AE index indicates effects of both prompt penetration electric field and disturbance dynamo electric field, consistent with previous studies based on F region equatorial vertical plasma drift measurements at Jicamarca. The average response of the equatorial electrojet to geomagnetic storms (Dststorm" effect is found to depend on the magnitude of the storm, solar EUV activity, season, and longitude.

  7. Observations of substorm fine structure

    L. L. Lazutin

    Full Text Available Particle and magnetic field measurements on the CRRES satellite were used, together with geosynchronous satellites and ground-based observations, to investigate the fine structure of a magnetospheric substorm on February 9, 1991. Using the variations in the electron fluxes, the substorm activity was divided into several intensifications lasting about 3–15 minutes each. The two main features of the data were: (1 the intensifications showed internal fine structure in the time scale of about 2 minutes or less. We call these shorter periods activations. Energetic electrons and protons at the closest geosynchronous spacecraft (1990 095 were found to have comparable activation structure. (2 The energetic (>69 keV proton injections were delayed with respect to electron injections, and actually coincided in time with the end of the intensifications and partial returns to locally more stretched field line configuration. We propose that the energetic protons could be able to control the dynamics of the system locally be quenching the ongoing intensification and possibly preparing the final large-scale poleward movement of the activity. It was also shown that these protons originated from the same intensification as the preceeding electrons. Therefore, the substorm instability responsible for the intensifications could introduce a negative feedback loop into the system, creating the observed fine structure with the intensification time scales.

    Key words. Magnetospheric Physics (Storms and substorms.

  8. Dynamics of the auroral electrojets and their mapping to the magnetosphere

    Data of the EISCAT and IMAGE magnetic observatories chains in combination with data of three Russian observatories (St. Petersburg, Borok and Moscow) were used to determine the eastward and westward electrojet dynamics in the course of magnetic storms. During the storm main phase and maximum substorm intensity the eastward electrojet is located at latitudes lower than usual. During intervals between substorms the westward electrojet centre shifts equatorwards as Dst increases. At a substorm maximum the westward electrojet widens polewards. The spectrograms of precipitating electrons and ions of auroral energies obtained onboard the DMSP F8, F10 and F11 satellites allow to connect the regions of the electrojet location with characteristic plasma structures at ionospheric altitudes. The eastward electrojet in the evening sector is located in the region of diffuse electron precipitations. The electrojet centre coincides with the latitude of an energy flux maximum of auroral protons. In the course of substorms the westward electrojet at the nightside is located at latitudes of both diffuse and discrete electron precipitations. The electrojets and plasma region boundaries are mapped to the magnetosphere. The paraboloid model of the magnetosphere is used here. The influence of paraboloid model input parameters on the dayside cusp latitude, on the ionospheric boundaries between open and closed as well as dipole-like and tail-like field lines is considered. It is shown that tail currents influence magnetic field line configuration in the nightside magnetosphere stronger than the ring current

  9. Precipitation of low energy electrons at high latitudes: Effects of substorms, interplanetary magnetic field and dipole tilt angle

    Burch, J. L.


    Data from the auroral particles experiment on OGO-4 were used to study effects of substorm activity, interplanetary magnetic field latitutde, and dipole tilt angle on high-latitude precipitation of 700 eV electrons. It was found that: (1) The high-latitude zone of 700 eV electron precipitation in late evening and early morning hours moves equatorward by 5 to 10 deg during substorms. (2) The low-latitude boundary of polar cusp electron precipitation at 9 to 15 hours MLT also moves equatorward by several degrees during substorms and, in the absence of significant substorm activity, after a period of southward interplanetary magnetic field. (3) With times containing substorm activity or a southward interplanetary magnetic field eliminated, the low-latitude boundary of polar cusp electron precipitation is found to move by approximately 4 deg over the total yearly range of tilt angles. At maximum winter and summer conditions the invariant latitude of the boundary is shown to shift by approximately -3 deg and +1 deg respectively from its equinox location.

  10. Substorm topology in the ionosphere and magnetosphere during a flux rope event in the magnetotail

    O. Amm


    Full Text Available On 13 August 2002, at ~23:00 UT, about 10 min after a substorm intensification, Cluster observes a flux rope in the central magnetotail, followed by a localised fast flow event about oneminute later. Associated with the flux rope event, a traveling compression region (TCR is seen by those Cluster spacecraft which reside in the lobe. In the conjugate ionospheric region in Northern Scandinavia, the MIRACLE network observes the ionospheric equivalent currents, and the electron densities and electric fields are measured by the EISCAT radar along a meridional scanning profile. Further, the auroral evolution is observed with the Wideband Imaging Camera (WIC on the IMAGE satellite. We compare in detail the substorm evolution as observed in the ionosphere and in the magnetosphere, and examine whether topological correspondences to the flux rope event exist in the ionospheric signatures. The large-scale mapping of both the location and the direction of the flux rope to the ionosphere shows an excellent correspondence to a lens-shaped region of an auroral emission minimum. This region is bracketed by an auroral region equatorward of it which was preexisting to the substorm intensification, and a substorm-related auroral region poleward of it. It is characterised by reduced ionospheric conductances with respect to its environment, and downward field-aligned current (FAC observed both in the magnetosphere and in the ionosphere. As determined from the ionospheric data, this downward FAC area is moving eastward with a speed of ~2 km s-1, in good agreement with the mapped plasma bulk velocity measured at the Cluster satellite closest to that area. Further southwestward to this leading downward FAC area, a trailing upward FAC area is observed that moves eastward with the same speed. The direction of the ionospheric electric field permits a current closure between these two FAC areas through the ionosphere. We speculate that these FAC areas may

  11. Auroral images and particle precipitations observed by S-310JA-8, -9, and -10 at Syowa Station

    Three sounding rockets were launched in 1984 from Syowa Station in Antarctica into different types of aurora, designated as AURORA I (an active auroral arc at the substorm expansion phase), II (a stable are prior to the substrom onset) and III (a diffuse aurora during the recovery phase). A new television camera was used to take an auroral picture, together with the electron spectrometers to measure the energy spectrum of auroral particles. AURORA I showed greater values in both auroral emission and electron density than for AURORA II. In AURORA III, although the auroral emission intensity was much less in comparison with AURORA I, the electron density showed a pronounced enhancement in the D-region and was comparable with the case of AURORA I above the E-region. As for an energy spectrum of auroral electrons, AURORA I and II showed an inverted-V type monoenergetic peak with much higher energy for AURORA I than for AURORA II, whereas AURORA III exhibits a power-law spectrum with a small superposing monoenergetic peak around 0.5 keV above 200 km in altitude. The television camera showed a dependence of auroral color spectrum on the auroral activity, i.e., the ratio of an apparent emission rate at 427.8 nm and an illuminance in a visible range (400 to 800 nm) becomes greater for brighter aurora. (author)

  12. On principal factors in substorm models

    朱岗; 洪明华


    This paper gives a brief account of substorm modeling with different key elements or factors. The progress of our understanding of substorms consists of three chief stages during this century. Nine previous substorm models are briefly recapitulated, and then a recent two neutral-points model by Prof. C.T. Russell is introduced. In order to test or to strengthen this new model, several correlated examples of meaningful data are duly given in this short paper.

  13. The expansive phase of magnetospheric substorms 2. The response at synchronous altitude of particles of different energy ranges

    Several previous studies have shown that there are variations in the energetic particle populations at synchronous orbit during periods of substorm activity; however, in these investigations the precise location of the satellite with respect to the longitudinal regime experiencing expansion phase activity has been unknown. In this paper, data from the Lockheed particle detectors on ATS 5 in synchronous orbit and from the meridian line of magnetometers operated by the University of Alberta are correlated for periods of substorm activity where the position of the satellite with respect to the expansion phase regime is known. It is found that changes in the nature of the energetic particle signatures at ATS 5 are correlated with changes in the auroral electrojet structure during the development of the substorm expansive phase. In particular, it is found that marked increases in the fluxes of the energetic particles showing no dispersion among the energy channels occur only when the satellite is on field lines which map to the poleward border of the substorm-intensified westward electrojet. It is further found that when the satellite is on field lines which penetrate the heart of the substorm westward electrojet, one only observes steady high fluxes of energetic particles, and there are no sharp well-defined changes in fluxes associated with continuing impulsive intensifications of the electrojet at its poleward border. It is concluded that the substorm disturbance typically begins at a given latitude and propagates poleward steps and that energetic electron enhancements are observed at ATS 5 when the poleward border of the electrojet intensifies in the latitude range of the ATS field line foot. This fact permits the mapping of field lines in the geographic equatorial plane to the earth's surface at specific instants during the substorm expansion phase

  14. Interhemispheric asymmetries in the occurrence of magnetically conjugate sub-auroral polarisation streams

    Parkinson, M. L.; Pinnock, M.; Wild, J. A.; Lester, M.; Yeoman, T. K.; Milan, S. E.; Ye, H.; Devlin, J. C.; Frey, H. U.; Kikuchi, T.


    Earthward injections of energetic ions and electrons mark the onset of magnetospheric substorms. In the inner magnetosphere (L{sim}4), the energetic ions drift westward and the electrons eastward, thereby enhancing the equatorial ring current. Wave-particle interactions can accelerate these particles to radiation belt energies. The ions are injected slightly closer to Earth in the pre-midnight sector, leading to the formation of a radial polarisation field in the inner magnetosphere. This maps to a poleward electric field just equatorward of the auroral oval in the ionosphere. The poleward electric field is subsequently amplified by ionospheric feedback, thereby producing auroral westward flow channels (AWFCs). In terms of electric field strength, AWFCs are the strongest manifestation of substorms in the ionosphere. Because geomagnetic flux tubes are essentially equi-potentials, similar AWFC signatures should be observed simultaneously in the Northern and Southern Hemispheres. Here we present magnetically conjugate SuperDARN radar observations of AWFC activity observed in the pre-midnight sector during two substorm intervals including multiple onsets during the evening of 30 November 2002. The Northern Hemisphere observations were made with the Japanese radar located at King Salmon, Alaska (57circLambda ), and the Southern Hemisphere observations with the Tasman International Geospace Environment Radar (TIGER) located at Bruny Island, Tasmania (-55circLambda ). LANL geosynchronous satellite observations of energetic ion and electron fluxes monitored the effects of substorms in the inner magnetosphere (L{sim}6). The radar-observed AWFC activity was coincident with activity observed at geosynchronous orbit, as well as westward current surges in the ionosphere observed using ground-based magnetometers. The location of AWFCs with respect to the auroral oval was inferred from FUV auroral images recorded on board the IMAGE spacecraft. DMSP SSIES ion drift measurements

  15. The Four-Part Field-Aligned Current System in the Ionosphere at Substorm Onset

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


    Whereas the plasma circulation in the ionosphere is driven by convective drift which is the same for ions and electrons, the magnetospheric plasma circulation includes curvature and gradient drifts, which are charge-dependent. There is even a region of the Neutral Sheet in which the ions, but not the electrons, are "unmagnetized" and where charge separation can occur even for convective drift, which the electrons execute but the ions do not. Due to the charge separations in the magnetosphere, field-aligned currents are generated. The FACs and the associated electric fields play an important role in producing the convection pattern in the ionosphere. Here we argue that there are two pairs of FACs near substorm onset. One pair involves the auroral zone portion of the convection. There, a downward D FAC occurs in the poleward part of the auroral zone and an upward U FAC occurs in the equatorward part. We show that the D-U auroral FAC pair results from the odd situation in the INSh, where the electrons can convect earthward while the unmagnetized ions do not and so remain further tailward of the electrons. The equatorward edge of the auroral zone is marked by a convection reversal, because the auroral zone flows have an eastward velocity component, whereas subauroral flows have a westward component. At the convection reversal, the flow is strictly southward and the electric field strictly westward. The subauroral zone maps out to the outer radiation belt, where the high-energy electrons precipitate tailward of the energetic electron trapping boundary,and high-energy ions precipitate tailward of the energetic ion trapping boundary, the latter being earthward of the former. As a result, another FAC pair forms on field lines in the ORB/subauroral regions. The U FAC of the latter region is adjacent but earthward of the U FAC of the auroral zone pair. The D-U auroral zone pair is poleward of the U-D subauroral (Radiation Belt) pair. Finally, we note that the electric field

  16. THEMIS observation of a substorm event on 04:35, 22 February 2008

    J. Liu


    Full Text Available We report on THEMIS in-situ and ground-based observations during a substorm between 04:30~04:50 UT on 22 February 2008. The spacecraft (probes were aligned along the tail between XGSM=−5 RE to −25 RE. The most distant probe P1 (X=−24.5 RE detected two successive tailward moving bipolar magnetic structures. P2 (X=−18 RE, P3 (X=−11 RE, P4 (X=−10.5 RE all captured signatures related to the Earthward movement of a magnetic structure. THEMIS ground stations and all-sky imagers also recorded Pi2 pulsations and a sudden brightening in a white-light auroral imager followed by poleward expansion. We perform a detailed timing analysis of probe and ground-based data and reconstruct the time sequence of phenomena during this substorm. The earliest sign of substorm onset was the bipolar perturbation in the northward component of the magnetic field (interpreted as the result of reconnection onset at P1 at 04:35:16 UT and corresponding magnetic perturbation at P2 at 04:35:14 UT. Auroral onset was seen at or before 04:36:55 UT, consistent with the visual onset of high-latitude magnetic pulsations at around that time. Earthward flows at P3 and P4 seen at ~04:36:03 UT, and dipolarization onset at ~04:36:50 UT, were observed at almost the same time as the ground onset signature, implying that near-Earth dipolarization happened in the aftermath of tail reconnection but not significantly ahead of the auroral intensification. Reconnection in the tail preceded ground onset and near-Earth dipolarization (current disruption by ~2 min. Two reconnection pulses (the first one weaker than the second one accompanied by correlative increases of cumulative magnetic flux transfer into the reconnection region were observed. A direct association of the reconnection pulses with two auroral intensifications can be made

  17. Characterization and diagnostic methods for geomagnetic auroral infrasound waves

    Oldham, Justin J.

    Infrasonic perturbations resulting from auroral activity have been observed since the 1950's. In the last decade advances in infrasonic microphone sensitivity, high latitude sensor coverage, time series analysis methods and computational efficiency have elucidated new types of auroral infrasound. Persistent periods of infrasonic activity associated with geomagnetic sub-storms have been termed geomagnetic auroral infrasound waves [GAIW]. We consider 63 GAIW events recorded by the Fairbanks, AK infrasonic array I53US ranging from 2003 to 2014 and encompassing a complete solar cycle. We make observations of the acoustic features of these events alongside magnetometer, riometer, and all-sky camera data in an effort to quantify the ionospheric conditions suitable for infrasound generation. We find that, on average, the generation mechanism for GAIW is confined to a region centered about ~60 0 longitude east of the anti-Sun-Earth line and at ~770 North latitude. We note furthermore that in all cases considered wherein imaging riometer data are available, that dynamic regions of heightened ionospheric conductivity periodically cross the overhead zenith. Consistent features in concurrent magnetometer conditions are also noted, with irregular oscillations in the horizontal component of the field ubiquitous in all cases. In an effort to produce ionosphere based infrasound free from the clutter and unknowns typical of geophysical observations, an experiment was undertaken at the High Frequency Active Auroral Research Program [HAARP] facility in 2012. Infrasonic signals appearing to originate from a source region overhead were observed briefly on 9 August 2012. The signals were observed during a period when an electrojet current was presumed to have passed overhead and while the facilities radio transmitter was periodically heating the lower ionosphere. Our results suggest dynamic auroral electrojet currents as primary sources of much of the observed infrasound, with

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

    A. Keiling


    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.

  19. Auroral Tomography Workshop, Proceedings

    In ionospheric and atmospheric physics the importance of multi-station imaging has grown as a consequence of the availability of scientific grade CCD cameras with digital output and affordable massive computing power. Tomographic inversion techniques are used in many different areas, e.g. medicine, plasma research and space physics. The tomography workshop was announced to gather a limited group of people interested in auroral tomography or tomographic inversion methods in general. ALIS (Auroral Large Imaging System) is a multi-station ground-based system developed primarily for three-dimensional auroral imaging, however other non-auroral objects can be studied with ALIS, e.g. stratospheric clouds. Several of the contributions in the workshop dealt with problems related to geometries similar to the ALIS-configuration. The Proceedings contain written contributions received either in abstract form or as full papers. The Proceedings also contain contributions intended for the Workshop but not presented due to the absence of the speaker. Separate abstracts have been prepared for 15 of the 17 papers

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

    N. C. Draper


    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

  1. Longitudinal (UT effect in the onset of auroral disturbances over two solar cycles as deduced from the AE-index

    L. A. Hajkowicz

    Full Text Available Statistical study on the universal time variations in the mean hourly auroral electrojet index (AE-index has been undertaken for a 21 y period over two solar cycles (1957–1968 and 1978–1986. The analysis, applied to isolated auroral substorm onsets (inferred from rapid variations in the AE-index and to the bulk of the AE data, indicates that the maximum in auroral activity is largely confined to 09–18 UT, with a distinct minimum at 03–06 UT. The diurnal effect was clearly present throughout all seasons in the first cycle but was mainly limited to northern winter in the second cycle. Severe storms (AE > 1000 nT tended to occur between 9–18 UT irrespective of the seasons whereas all larger magnetic disturbances (AE > 500 nT tended to occur in this time interval mostly in winter. On the whole the diurnal trend was strong in winter, intermediate at equinox and weak in summer. The implication of this study is that Eastern Siberia, Japan and Australia are mostly at night, during the period of maximum auroral activity whereas Europe and Eastern America are then mostly at daytime. The minimum of auroral activity coincides with near-midnight conditions in Eastern America. It appears that the diurnal UT distribution in the AE-index reflects a diurnal change between interplanetary magnetic field orientation and the Earth's magnetic dipole inclination.

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

  2. The reason for magnetospheric substorms and solar flares

    It has been proposed that magnetospheric substorms and solar flares are a result of the same mechanism. In our view this mechanism is connected with the escape, or attempted escape, of energized plasma from a region of closed magnetic field lines bounded by a magnetic bottle. In the case of the Earth, it must be plasma that is a able to maintain a discrete auroral arc, and we propose that the cross-tail current connected to the arc is filamentary in nature to provide the field-aligned current sheet above the arc. A localized meander of such an intense current filament could be caused by a tearing instability in the neutral sheet. Such a meander will cause an inductive electric field opposing the current change everywhere. In trying to reduce the component of the induction electric field parallel to the magnetic field lines, the plasma must enhance the transverse or cross-tail component; this action leads to eruptive behavior, in agreement with tearing theories. This enhanced induction electric field will cause a discharge along the magnetic neutral line at the apex of the magnetic arches, constituting an impulsive acceleration of all charged particles originally near the neutral line. The products of this phase then undergo betatron acceleration for a second phase. This discharge eventually reduces the electric field along the neutral line, and thereafter the enclosed magnetic flux through the neutral line remains nearly constant. The result is a plasmoid that has definite identity; its buoyancy leads to its escape. The auroral breakup (and solar flare) is the complex plasma response to the changing electromagnetic field. (orig.)

  3. Penetration dynamics of the ring current into the plasmasphere during substorms by the observation of diffuse aurora and SAR arc

    Complete text of publication follows. Observations of the diffuse aurora (DA) and stable auroral red (SAR) arc are the informative investigation method of magnetosphere-ionosphere coupling in the vicinity of plasmapause and inner boundary of the plasma sheet during magnetospheric disturbances. SAR arcs are the consequence of interaction of the outer plasmasphere (plasmapause) with energetic ions of the ring current. The DA is caused by the low-energy electron precipitation from the plasma sheet. During substorms we observe the intensity increase of DA and its equatorward extension up to the plasmapause projection which is mapped by the SAR arc occurring at that time. (Ievenko et al, Adv. Space Res., 2008). In this work we present the new study results of the DA and SAR arc dynamics based on spectrophotometric observations at the Yakutsk meridian (199deg E geomagnetic longitude). For individual events the relationship of equatorward extension of the DA in the 557,7 nm emission to the magnetospheric convection intensification after the turn of IMF BZ to the south is shown. The longitudinal dynamics of SAR arc formation during the substorm expansion phase is investigated. The connection of SAR arc occurrence with the substorm injection by the geosynchronous measurements is analyzed. It is assumed that the interval of latitudes where SAR arcs are observed during weak and moderate storms is a statistical map of the outer plasmasphere region, into which the developing ring current penetrates and damps during substorms.

  4. Far ultraviolet auroral imager

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


    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°.

  5. Aftereffects of isolated magnetospheric substorm activity on the Mid-Latitude ionosphere: Localized depressions in F layer electron densities

    Ground-based ionosonde data from a global network of about 100 stations have been used to study ionospheric disturbances at mid-latitudes associated with isolated magnetospheric substorm activity. The results of four case studies during solstice periods are presented here. In each case, pronounced (approx.10-30%) depressions in ∫0F2 developed in a limited longitude sector in the summer hemispher and lasted for about 1 day. The region of depressed ∫0F2 appears as a tongue extending from the auroral zone down to about 20degree geomagnetic latitude and corotating with the earth. This region is found to have been on the dayside of the earth while the substorm activity was in progress. It is suggested that these depressions are caused by changes in the thermospheric composition and that the primary heat source for the thermospheric disturbances is Joule heating in the dayside polar cusp region

  6. THEMIS observations of double-onset substorms and their association with IMF variations

    C.-C. Cheng


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

    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.

  8. Interaction of dipolarization fronts within multiple bursty bulk flows in global MHD simulations of a substorm on 27 February 2009

    Ge, Y. S.; Raeder, J.; Angelopoulos, V.; Gilson, M. L.; Runov, A.


    We performed a global MHD simulation of a well-studied substorm on 27 February 2009 (Runov et al., 2009) to understand the generation and large-scale evolution of dipolarization fronts within bursty bulk flows (BBFs). Conjugate, well-positioned Time History of Events and Macroscale Interactions During Substorms (THEMIS) observations from space and ground observatories provide significant constraints to the simulation model. The main substorm onset auroral brightening, at 0749 UT, was in the field of view of Fort Smith (FSMI), just poleward of a preexisting auroral arc. Two minutes later, the space probes recorded a sharp dipolarization front moving sunward, passing by THEMIS and traversing ˜10 RE along the magnetotail. Our global MHD model, OpenGGCM, driven by real-time solar wind/interplanetary magnetic field conditions, is able to reproduce the key features of these signatures. We show that the auroral breakup is caused by the strong flow shear and the flow vortices formed by the BBF flows. Rebound oscillations of the intruding BBF (consistent with recent observations by Panov et al. (2010a)) and filamentation of the front into 1 RE size undulations are superimposed on the flow pattern. Further investigation of the interaction of the BBF and the dipolarization fronts (DFs) reveals that an observed bipolar Bz signature ahead of the DF is due to the interaction between two distinct plasmas emanating from multiple X lines: antisunward-moving flux tubes from a reconnection region at ˜13 RE and sunward-moving dipolarization region within a BBF from a midtail reconnection region at ˜23 RE.

  9. The Ionospheric Model Adaptation to the Auroral Latitudes With UHF EISCAT Radar and Tromso Magnetometer Data

    Nikolaeva, Vera; Gordeev, Evgeny; Kotikov, Andrey

    E-layer Auroral Ionosphere Model (E-AIM) developed in Arctic and Antarctic Research Institute can provide temporal and spatial distribution of the main ionosphere parameters: ion and electron density distribution in the altitude range from 90 to 150 km. The statistical study of E-layer electron density dependence on substorm activity was made to improve model results in high latitudes. About fifty substorms were included to the data analysis. Particular attention was paid to the dynamics of magnetic disturbances and ionospheric parameters measured by the radar. Correlation of electron density values measured by the UHF EISCAT incoherent scattering radar with geomagnetic indices was determined. Applicability of geomagnetic indices as input parameters of the local E-AIM model was estimated.

  10. Altitude Variations of the Peak Auroral Emissions within Auroral Structures

    Sangalli, L.


    The MIRACLE network monitors auroral activity in the Fennoscandian sector of Europe. Network stations cover the range of 55° to 57° magnetic latitude North and span two hours in magnetic local time. Some of the MIRACLE network stations include digital all-sky cameras (ASC) with overlapping field-of-views located at the latitude aurora occurs. The ASCs in this network operate at three different wavelengths: 427.8 nm (blue line), 557.7 nm (green line) and 630.0 nm (red line). These wavelengths are selected using narrow band filters. The new ASC systems are based on electron multiplying CCDs (emCCD), which allow higher time and spatial resolutions. The peak auroral emission altitude is determined using two ASC images from a station pair. Different auroral events are used to evaluate the altitude variations of the peak auroral emissions within auroral structures and its evolution in time.

  11. Large scale patterns of auroral ionospheric convection observed with the Chatanika radar

    Ionospheric convection at auroral latitudes has been examined during a series of long duration experiments with the Chatanika, Alaska, incoherent scatter radar. These experiments have been carefully designed to obtain maximum latitudinal coverage (56 0Λ to 75 0Λ) while maintaining a temporal resolution of 30 min in order to resolve the effects of individual substorms on the convection pattern. Design criteria for the experiments are described together with presentation of observational data acquired during 400 hr of radar operations during various levels of geophysical disturbance. The data accentuate the repeatability of the gross features of the auroral convection and its basic conformity to the two0cell pattern predicted from the large-scale magnetospheric circulation. For moderate to active geomagnetic conditions uniform sunward convection with velocities of 800 to 1200 m/s spans the 62 0Λ to 72 0Λ latitude band at both dawn and dusk. In quieter circumstances the sunward convection continues in this region, but has smaller speeds and is centered at higher latitudes. Little evidence of a throat in the dayside convection pattern is seen at latitudes below 75 0Λ except in very disturbed circumstances. During several experiments coordinated operation of the Chatanika and Millstone Hill, Massachusetts, radars permitted the simultaneous observation of the auroral convection pattern at two different local times. substorms affect the convection at all local times and appears to generally enhance the rate of convection without seriously changing its direction. Near midnight, latitudinal displacements and expansions of the convection pattern during substorms may result in a local rotation or reversal of the direction of convection, while near dawn and dusk, convection velocities are enhanced and the region of sunward flow expands to lower latitudes

  12. Energy density of ionospheric and solar wind origin ions in the near-Earth magnetotail during substorms

    Daglis, Loannis A.; Livi, Stefano; Sarris, Emmanuel T.; Wilken, Berend


    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

  13. The auroral electron accelerator

    A model of the auroral electron acceleration process is presented in which the electrons are accelerated resonantly by lower-hybrid waves. The essentially stochastic acceleration process is approximated for the purposes of computation by a deterministic model involving an empirically derived energy transfer function. The empirical function, which is consistent with all that is known of electron energization by lower-hybrid waves, allows many, possibly all, observed features of the electron distribution to be reproduced. It is suggested that the process occurs widely in both space and laboratory plasmas. (author)

  14. Auroral electron acceleration

    Two theories of auroral electron acceleration are discussed. Part 1 examines the currently widely held view that the acceleration is an ordered process in a quasi-static electric field. It is suggested that, although there are many factors seeming to support this theory, the major qualifications and uncertainties that have been identified combine to cast serious doubt over its validity. Part 2 is devoted to a relatively new interpretation in terms of stochastic acceleration in turbulent electric fields. This second theory, which appears to account readily for most known features of the electron distribution function, is considered to provide a more promising approach to this central question in magnetospheric plasma physics. (author)

  15. Auroral Current and Electrodynamics Structure Measured by Two SOunding Rockets in Flight Simultaneously

    Bounds, Scott R.; Kaeppler, Steve; Kletzing, Craig; Lessard, Marc; Cohen, Ian J.; Jones, Sarah; Pfaff, Robert F.; Rowland, Douglas E.; Anderson, Brian Jay; Gjerloev, Jesper W.; Labelle, James W.; Dombrowski, Micah P.; Dudok de Wit, Thierry; Heinselman, Craig J.


    On January 29, 2009, two identically instrumented sounding rockets were launched into a sub-storm auroral arc from Poker Flat Alaska. Labeled the Auroral Currents and Electrodynamics Structure (ACES) mission, the payloads were launched to different apogees (approx.350km and approx.120km) and staggered in time so as to optimize their magnetic conjunctions. The different altitudes provided simultaneous in-situ measurements of magnetospheric input and output to the ionosphere and the ionospheric response in the lower F and E region. Measurements included 3-axis magnetic field, 2-axis electric field nominally perpendicular to the magnetic field, energetic particles, electron and ion, up to 15keV, cold plasma temperature and density. In addition, PFISR was also operating in a special designed mode to measure electric field and density profiles in the plane defined by the rocket trajectories and laterally to either side of the trajectories. Observation of the measured currents and electrodynamics structure of the auroral form encountered are presented in the context of standard auroral models and the temporal/spatial limitations of mission designs.

  16. The optical manifestation of dispersive field-aligned bursts in auroral breakup arcs

    Dahlgren, H.; Semeter, J. L.; Marshall, R. A.; Zettergren, M.


    High-resolution optical observations of a substorm expansion show dynamic auroral rays with surges of luminosity traveling up the magnetic field lines. Observed in ground-based imagers, this phenomenon has been termed auroral flames, whereas the rocket signatures of the corresponding energy dispersions are more commonly known as field-aligned bursts. In this paper, observations of auroral flames obtained at 50 frames/s with a scientific-grade Complementary Metal Oxide Semiconductor (CMOS) sensor (30° × 30° field of view, 30 m resolution at 120 km) are used to provide insight into the nature of the precipitating electrons similar to high-resolution particle detectors. Thanks to the large field of view and high spatial resolution of this system, it is possible to obtain a first-order estimate of the temporal evolution in altitude of the volume emission rate from a single sensor. The measured volume emission rates are compared with the sum of modeled eigenprofiles obtained for a finite set of electron beams with varying energy provided by the TRANSCAR auroral flux tube model. The energy dispersion signatures within each auroral ray can be analyzed in detail during a fraction of a second. The evolution of energy and flux of the precipitation shows precipitation spanning over a large range of energies, with the characteristic energy dropping from 2.1 keV to 0.87 keV over 0.2 s. Oscillations at 2.4 Hz in the magnetic zenith correspond to the period of the auroral flames, and the acceleration is believed to be due to Alfvenic wave interaction with electrons above the ionosphere.

  17. MESSENGER Observations of Substorm Activity at Mercury

    Sun, W. J.; Slavin, J. A.; Fu, S.; Raines, J. M.; Zong, Q. G.; Poh, G.; Jia, X.; Sundberg, T.; Gershman, D. J.; Pu, Z.; Zurbuchen, T.; Shi, Q.


    MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma measurements taken during crossings of Mercury's magnetotail from 2011 to 2014 have been investigated for substorms. A number of events with clear Earth-like growth phase and expansion phase signatures were found. The thinning of the plasma sheet and the increase of magnetic field intensity in the lobe were observed during the growth phase and plasma sheet was observed to thicken during the expansion phase, which are similar to the observations at Earth. But the time scale of Mercury's substorm is only several minutes comparing with the several hours at Earth [Sun et al., 2015a]. Detailed analysis of magnetic field fluctuations during the substorm expansion phase have revealed low frequency plasma waves, e.g. Pi2-like pulsations. The By fluctuations accompanying substorm dipolarizations are consistent with pulses of field-aligned currents near the high latitude edge of the plasma sheet. Further study shows that they are near-circularly polarized electromagnetic waves, most likely Alfvén waves. Soon afterwards the plasma sheet thickened and MESSENGER detected a series of compressional waves. We have also discussed their possible sources [Sun et al., 2015b]. Sun, W.-J., J. A. Slavin, S. Y. Fu, et al. (2015a), MESSENGER observations of magnetospheric substorm activity in Mercury's near magnetotail. Geophys. Res. Lett., 42, 3692-3699. doi: 10.1002/2015GL064052.Sun, W.-J., J. A. Slavin, S. Y. Fu, et al. (2015b), MESSENGER observations of Alfvénic and compressional waves during Mercury's substorms. Geophys. Res. Lett., 42, in press. doi: 10.1002/ 2015GL065452.

  18. Substorm electric fields at nightside low latitude

    Hashimoto, K. K.; Kikuchi, T.; Tomizawa, I.; Nagatsuma, T.


    The convection electric field penetrates from the polar ionosphere to low latitude and drives the DP2 currents in the global ionosphere with an intensified equatorial electrojet (EEJ). The electric field often reverses its direction, that is, the overshielding occurs and causes the equatorial counterelectrojet (CEJ) during storm and substorms. In this paper we report that the overshielding electric field is detected by the HF Doppler sounders at low latitude on the nightside. We analyzed the Doppler frequency of the HF radio signals propagated over 120 km in Japan at frequencies of 5 and 8 MHz and compared with the equatorial EEJ/CEJ during the substorm expansion phase. We found that the overshielding electric field reaches around 2 mV/m during major substorms (AL <-1800 nT). Taking the geometrical attenuation into account, we estimate the equatorial electric field to be about 1.5 mV/m. We also found that the correlation coefficient was 0.94 between the overshielding electric field and eastward equatorial electrojet at YAP on the night side. The electric field drives the eastward electrojets in the equatorial ionosphere on the night side. It is to be noted that the overshielding electric field is observed on the nightside at low latitude during the major substorms, while the convection electric field is dominant during smaller size substorms, as the CEJ flows on the dayside. These results suggest that the overshielding electric field associated with the Region-2 field-aligned currents becomes dominant during substorms at low latitude on the nightside as well as on the dayside.

  19. Auroral Spatial Structures Probe Project

    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...

  20. Observational study of generation conditions of substorm-associated low-frequency AKR emissions

    A. Olsson


    Full Text Available It has lately been shown that low-frequency bursts of auroral kilometric radiation (AKR are nearly exclusively associated with substorm expansion phases. Here we study low-frequency AKR using Polar PWI and Interball POLRAD instruments to constrain its possible generation mechanisms. We find that there are more low-frequency AKR emission events during wintertime and equinoxes than during summertime. The dot-AKR emission radial distance range coincides well with the region where the deepest density cavities are seen statistically during Kp>2. We suggest that the dot-AKR emissions originate in the deepest density cavities during substorm onsets. The mechanism for generating dot-AKR is possibly strong Alfvén waves entering the cavity from the magnetosphere and changing their character to more inertial, which causes the Alfvén wave associated parallel electric field to increase. This field may locally accelerate electrons inside the cavity enough to produce low-frequency AKR emission. We use Interball IESP low-frequency wave data to verify that in about half of the cases the dot-AKR is accompanied by low-frequency wave activity containing a magnetic component, i.e. probably inertial Alfvén waves. Because of the observational geometry, this result is consistent with the idea that inertial Alfvén waves might always be present in the source region when dot-AKR is generated. The paper illustrates once more the importance of radio emissions as a powerful remote diagnostic tool of auroral processes, which is not only relevant for the Earth's magnetosphere but may be relevant in the future in studying extrasolar planets.

  1. Computer-simulation movie of ionospheric electric fields and currents for a magnetospheric substorm life cycle. Technical note

    Numerical solution of the current conservation equation gives the distributions of electric fields and currents in the global ionosphere produced by the field-aligned currents. By altering ionospheric conductivity distributions as well as the field-aligned current densities and configurations to simulate a magnetospheric substorm life cycle, which is assumed to last for five hours, various patterns of electric fields and currents are computed for every 30-second interval in the life cycle. The simulated results are compiled in the form of a color movie, where variations of electric equi-potential curves are the first sequence, electric current-vector changes are the second, and fluctuations of the electric current system are the third. The movie compresses real time by a factor of 1/180, taking 1.7 minutes of running time for one sequence. One of the most striking features of this simulation is the clear demonstration of rapid and large scale interactions between the auroral zone and middle-low latitudes during the substorm sequences. This technical note provides an outline of the numerical scheme and world-wide contour maps of the electric potential, ionospheric current vectors, and the equivalent ionospheric current system at 5-minute intervals as an aid in viewing the movie and to further detailed study of the 'model' substorms

  2. Multiscale and cross entropy analysis of auroral and polar cap indices during geomagnetic storms

    Gopinath, Sumesh; Prince, P. R.


    In order to improve general monoscale information entropy methods like permutation and sample entropy in characterizing the irregularity of complex magnetospheric system, it is necessary to extend these entropy metrics to a multiscale paradigm. We propose novel multiscale and cross entropy method for the analysis of magnetospheric proxies such as auroral and polar cap indices during geomagnetic disturbance times. Such modified entropy metrics are certainly advantageous in classifying subsystems such as individual contributions of auroral electrojets and field aligned currents to high latitude magnetic perturbations during magnetic storm and polar substorm periods. We show that the multiscale entropy/cross entropy of geomagnetic indices vary with scale factor. These variations can be attributed to changes in multiscale dynamical complexity of non-equilibrium states present in the magnetospheric system. These types of features arise due to imbalance in injection and dissipation rates of energy with variations in magnetospheric response to solar wind. We also show that the multiscale entropy values of time series decrease during geomagnetic storm times which reveals an increase in temporal correlations as the system gradually shifts to a more orderly state. Such variations in entropy values can be interpreted as the signature of dynamical phase transitions which arise at the periods of geomagnetic storms and substorms that confirms several previously found results regarding emergence of cooperative dynamics, self-organization and non-Markovian nature of magnetosphere during disturbed periods.

  3. Modes of high-latitude auroral conductance variability derived from DMSP energetic electron precipitation observations: Empirical orthogonal function analysis

    McGranaghan, Ryan; Knipp, Delores J.; Matsuo, Tomoko; Godinez, Humberto; Redmon, Robert J.; Solomon, Stanley C.; Morley, Steven K.


    We provide the first ever characterization of the primary modes of ionospheric Hall and Pedersen conductance variability as empirical orthogonal functions (EOFs). These are derived from six satellite years of Defense Meteorological Satellite Program (DMSP) particle data acquired during the rise of solar cycles 22 and 24. The 60 million DMSP spectra were each processed through the Global Airlglow Model. Ours is the first large-scale analysis of ionospheric conductances completely free of assumption of the incident electron energy spectra. We show that the mean patterns and first four EOFs capture ˜50.1 and 52.9% of the total Pedersen and Hall conductance variabilities, respectively. The mean patterns and first EOFs are consistent with typical diffuse auroral oval structures and quiet time strengthening/weakening of the mean pattern. The second and third EOFs show major disturbance features of magnetosphere-ionosphere (MI) interactions: geomagnetically induced auroral zone expansion in EOF2 and the auroral substorm current wedge in EOF3. The fourth EOFs suggest diminished conductance associated with ionospheric substorm recovery mode. We identify the most important modes of ionospheric conductance variability. Our results will allow improved modeling of the background error covariance needed for ionospheric assimilative procedures and improved understanding of MI coupling processes.

  4. Cluster observation of plasma flow reversal in the magnetotail during a substorm

    A. T. Y. Lui


    Full Text Available We investigate in detail a reversal of plasma flow from tailward to earthward detected by Cluster at the downstream distance of ~19 RE in the midnight sector of the magnetotail on 22 August 2001. This flow reversal was accompanied by a sign reversal of the Bz component and occurred during the late substorm expansion phase as revealed by simultaneous global view of auroral activity from IMAGE. We examine the associated Hall current system signature, current density, electric field, Lorentz force, and current dissipation/dynamo term, the last two parameters being new features that have not been studied previously for plasma flow reversals. It is found that (1 there was no clear quadrupole Hall current system signature organized by the flow reversal time, (2 the x-component of the Lorentz force did not change sign while the other two did, (3 the timing sequence of flow reversal from the Cluster configuration did not match tailward motion of a single plasma flow source, (4 the electric field was occasionally dawnward, producing a dynamo effect, and (5 the electric field was occasionally larger at the high-latitude plasma sheet than near the neutral sheet. These observations are consistent with the current disruption model for substorms in which these disturbances are due to shifting dominance of multiple current disruption sites and turbulence at the observing location.

  5. Substorm simulation: Insight into the mechanisms of initial brightening

    Ebihara, Y.; Tanaka, T.


    Initial brightening of the aurora is an optical manifestation of the beginning of a substorm expansion and is accompanied by large-amplitude upward field-aligned currents (FACs). Based on global magnetohydrodynamic simulation, we suggest the possible generation mechanism of the upward FAC that may manifest the initial brightening. (1) A formation of the near-Earth neutral line (NENL) releases the tension force that accelerates plasma earthward. (2) The earthward (perpendicular) flow is converted to a field-aligned flow when flow braking takes place. (3) A high-pressure region propagates earthward along a field line. (4) The off-equatorial high-pressure region pulls in and discharges ambient plasma, which generates a flow vorticity around it. (5) Region 1-sense FAC is generated in the upper part of the off-equatorial high-pressure region. (6) The upward FAC is connected with the ionosphere in the center of the Harang discontinuity, causing the initial brightening. Additional dynamo is generated in the near-Earth region, which transmits electromagnetic energy. Upward FAC that manifests the initial brightening seems to be necessarily originated in the near-Earth off-equatorial region where the magnitude of the perpendicular (diamagnetic) current is relatively small in comparison with that of the FAC. Near the equatorial plane, the perpendicular current is comparable to or larger than FAC so that a current line is diverted from a magnetic field line and that the FAC generated near the equatorial plane is not necessarily connected with the ionosphere. The proposed mechanism occurs regardless of the location of the NENL and may explain some of auroral forms.

  6. Interhemispheric asymmetries in the occurrence of magnetically conjugate sub-auroral polarisation streams

    M. L. Parkinson


    Full Text Available Earthward injections of energetic ions and electrons mark the onset of magnetospheric substorms. In the inner magnetosphere (L${sim}$4, the energetic ions drift westward and the electrons eastward, thereby enhancing the equatorial ring current. Wave-particle interactions can accelerate these particles to radiation belt energies. The ions are injected slightly closer to Earth in the pre-midnight sector, leading to the formation of a radial polarisation field in the inner magnetosphere. This maps to a poleward electric field just equatorward of the auroral oval in the ionosphere. The poleward electric field is subsequently amplified by ionospheric feedback, thereby producing auroral westward flow channels (AWFCs. In terms of electric field strength, AWFCs are the strongest manifestation of substorms in the ionosphere. Because geomagnetic flux tubes are essentially equi-potentials, similar AWFC signatures should be observed simultaneously in the Northern and Southern Hemispheres. Here we present magnetically conjugate SuperDARN radar observations of AWFC activity observed in the pre-midnight sector during two substorm intervals including multiple onsets during the evening of 30 November 2002. The Northern Hemisphere observations were made with the Japanese radar located at King Salmon, Alaska (57$^{circ}$$Lambda $, and the Southern Hemisphere observations with the Tasman International Geospace Environment Radar (TIGER located at Bruny Island, Tasmania (

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

    S. Machida


    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

  8. Ground and space observations of medium frequency auroral radio emissions

    Broughton, Matthew C.

    The auroral zone is a rich source of natural radio emissions that can be observed in space and at ground-level. By studying these waves, scientists can gain insight into the plasma processes that generate them and use the near-Earth space environment as a large-scale plasma physics laboratory. This thesis uses both ground-level and in situ observations to study two kinds of natural radio emissions. First, we report observations of a new kind of auroral radio emission. The waves have frequencies ranging from 1.3-2.2 MHz, bandwidths ranging from 90-272 kHz, and durations ranging from 16-355 s. Spectral analysis of the waveform data has revealed that the emission has a complex combination of at least three kinds of fine structures. For model auroral electron distributions, calculations indicate that Langmuir waves could be excited at frequencies consistent with observations. The remainder of the thesis discusses auroral medium frequency (MF) burst, an impulsive, broadband natural radio emission observed at ground-level within a few minutes of local substorm onset. LaBelle [2011] proposed that MF burst originates as Langmuir/Z-mode waves on the topside of the ionosphere that subsequently mode convert to L-mode waves and propagate to ground-level. Using continuous waveform measurements and combined observations with the Sondrestrom Incoherent Scatter Radar, we have performed two tests of this mechanism. The results of these tests are consistent with the mechanism described in LaBelle [2011]. A survey of 8,624 half-orbits of the DEMETER spacecraft has revealed 68 observations of bursty MF waves. We have compared the wave properties of these waves to those of MF burst and have found that although it is uncertain, the balance of the evidence suggests that the bursty MF waves observed with DEMETER are the same phenomenon as the ground-level MF burst. Finally, we have used numerical simulations to model both the fine structure of MF burst and to estimate the attenuation the

  9. Spatial monitoring of auroral emissions

    A ground based technique to monitor the three-dimensional distribution of auroral emissions is presented. The system is composed of two subsystems. A monochromatic imaging system with digitizing capability monitors the two-dimensional variation of auroral intensity with 50 degree field of view. A second height measuring system obtains in real time the height distribution of the auroral luminosity within the field of view of the imaging system. This paper is a report of the stepwise development of the complete system. The measurements will be carried out in the magnetic meridian plane through the EISCAT-site in Norway and the Kiruna Geophysical Institute. The operation of the optical system will as much as possible be combined with incoherent scatter radar measurements. (author)

  10. Method to locate the polar cap boundary in the nightside ionosphere and application to a substorm event

    A. T. Aikio


    Full Text Available In this paper we describe a new method to be used for the polar cap boundary (PCB determination in the nightside ionosphere by using the EISCAT Svalbard radar (ESR field-aligned measurements by the 42-m antenna and southward directed low-elevation measurements by the ESR 32 m antenna or northward directed low-elevation measurements by the EISCAT VHF radar at Tromsø. The method is based on increased electron temperature (Te caused by precipitating particles on closed field lines. Since the Svalbard field-aligned measurement provides the reference polar cap Te height profile, the method can be utilised only when the PCB is located between Svalbard and the mainland. Comparison with the Polar UVI images shows that the radar-based method is generally in agreement with the PAE (poleward auroral emission boundary from Polar UVI.

    The new technique to map the polar cap boundary was applied to a substorm event on 6 November 2002. Simultaneous measurements by the MIRACLE magnetometers enabled us to put the PCB location in the framework of ionospheric electrojets. During the substorm growth phase, the polar cap expands and the region of the westward electrojet shifts gradually more apart from the PCB. The substorm onset takes place deep within the region of closed magnetic field region, separated by about 6–7° in latitude from the PCB in the ionosphere. We interpret the observations in the framework of the near-Earth neutral line (NENL model of substorms. After the substorm onset, the reconnection at the NENL reaches within 3 min the open-closed field line boundary and then the PCB moves poleward together with the poleward boundary of the substorm current wedge. The poleward expansion occurs in the form of individual bursts, which are separated by 2–10 min, indicating that the reconnection in the magnetotail neutral line is impulsive. The poleward expansions of the PCB are followed

  11. The problem of the acceleration of electrons of the outer radiation belt and magnetospheric substorms

    Antonova, E. E.; Stepanova, M. V.


    Predicting of the location of the maximum in high-energy electron fluxes filling a new radiation belt is an endeavor being carried out by physicists studying the magnetosphere. We analyzed the data from the Defense Meteorological Satellite Program (DMSP) satellites and ground-based magnetometers obtained during geomagnetic storm on 8-9 October 2012. The minimum value of the disturbance storm time (Dst) was -111 nT, and the maximum in high-energy electron fluxes that appeared during the recovery phase was observed at L = 4 Re. At the same time, we analyzed the motion of the auroral oval toward lower latitudes and related substorm activity using the data of the low-orbiting DMSP satellites and the IMAGE magnetic meridian network. It was found from the DMSP satellites' measurements that the maximum of the energy density of precipitating ions, the maximum of the plasma pressure, and the most equatorial part of the westward auroral electrojet are all located at the 60° geomagnetic latitude. This value corresponds to L = 4 Re, i.e., it coincides with the location of the maximum in high-energy electron fluxes. This L-value also agrees with the predictions of the Tverskaya relation between the minimum in Dst variation and the location of the maximum of the energetic electron fluxes, filling a new radiation belt. The obtained results show that the location of this maximum could be predicted solely from the data of the auroral particle precipitations and/or ground-based magnetic observations.

  12. DEMETER observations of bursty MF emissions and their relation to ground-level auroral MF burst

    Broughton, M. C.; LaBelle, J.; Parrot, M.


    A survey of medium frequency (MF) electric field data from selected orbits of the Detection of Electro-Magnetic Emissions Transmitted from Earthquakes (DEMETER) spacecraft reveals 68 examples of a new type of bursty MF emissions occurring at high latitudes associated with auroral phenomena. These resemble auroral MF burst, a natural radio emission observed at ground level near local substorm onsets. Similar to MF burst, the bursty MF waves observed by DEMETER have broadband, impulsive frequency structure covering 1.5-3.0 MHz, amplitudes of 50-100 μV/m, an overall occurrence rate of ˜0.76% with higher occurrence during active times, and strong correlation with auroral hiss. The magnetic local time distribution of the MF waves observed by DEMETER shows peak occurrence rate near 18 MLT, somewhat earlier than the equivalent peak in the occurrence rate of ground level MF burst, though propagation effects and differences in the latitudes sampled by the two techniques may explain this discrepancy. Analysis of solar wind and SuperMAG data suggests that while the bursty MF waves observed by DEMETER are associated with enhanced auroral activity, their coincidence with substorm onset may not be as exact as that of ground level MF burst. One conjunction occurs in which MF burst is observed at Churchill, Manitoba, within 8 min of MF emissions detected by DEMETER on field lines approximately 1000 km southeast of Churchill. These observations may plausibly be associated with the same auroral event detected by ground level magnetometers at several Canadian observatories. Although it is uncertain, the balance of the evidence suggests that the bursty MF waves observed with DEMETER are the same phenomenon as the ground level MF burst. Hence, theories of MF burst generation in the ionosphere, such as beam-generated Langmuir waves excited over a range of altitudes or strong Langmuir turbulence generating a range of frequencies within a narrow altitude range, need to be revisited to

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

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

    -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...... mass ejections compounded by high-speed plasma streams from coronal holes. Geomagnetic storm of March 17, 2015 was the largest in the current solar cycle. The high-latitude ionosphere dynamics is studied using arrays of ground-based instruments including GPS receivers, HF radars, ionosondes, riometers...... by DMSP satellites. Equivalent ionospheric currents (EICs) are obtained from ground magnetometer data using the spherical elementary currents systems (SECS) technique developed by Amm and Viljanen (1999) that has been applied over the entire North American ground magnetometer network by Weygand et al...

  14. On storm weakening during substorm expansion phase

    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.

  15. Aurores boréales

    Génot, Vincent


    Aurores boréales photographiées près d'Abisko (Suède, 68°21'N,18°49'E) en décembre 1998 par Vincent Génot (chercheur au CESR - Centre d'Etudes Spatiales des Rayonnements -, Toulouse, France) & Stéphanie Michiels.

  16. Ionospheric control of auroral occurrence

    Complete text of publication follows. Analogous to color CRTs, the aurora is a visual manifestation of the bombardment of atomic and molecular neutrals in the upper atmosphere by magnetic field-guided energetic charged particles (mainly electrons) from above. Based on this framework, the magnetosphere is the source of energetic particles, whereas the ionosphere is merely a passive 'illuminated target'. However, it is not clear if the magnetosphere is acting along in the energization of the particles because the energization occurs at the magnetosphere-ionosphere interface. The discovery of suppression of auroral acceleration events in sunlight [Newell et al., 1996] provides a new interpretation - the ionosphere is also playing an active role in the auroral production. The auroral sunlight effect is often attributed to an ionospheric feedback mechanism in which the background ionospheric conductance determines if an acceleration is required. However, a relationship between the background ionospheric conductance and the aurora has not been identified. In this presentation, we provide solid evidence to confirm that the ionospheric conductance plays a key role in modulating auroral intensity to a degree that may surpass its source's manipulation. This study is based on 56,675 Earth's disk FUV images of the polar regions acquired by TIMED/GUVI between February 2002 and November 2007. It is found that the occurrence rate of visible aurora reduces when the polar ionosphere is exposed to sunlight. Furthermore, the energy flux carried by precipitating electrons shows anti-correlation with the ionospheric background conductance. Suppression of the auroral energy flux is also found to continue in twilight until the ionosphere is totally in darkness - a strong evidence of ionospheric manipulation because the magnetospheric sunlight condition does not change. The present study suggests a new mechanism that governs our space disturbances, in addition to the more familiar

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

    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

  18. Ionospheric current system accompanied by auroral vortex streets

    Hiraki, Yasutaka


    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...

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

    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...

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

    D. M. Willis

    geomagnetic storms are usually a feature of the declining phase of the solar cycle. In addition, the strength of such recurrent geomagnetic storms has been classified as moderate rather than intense. The recurrent geomagnetic storms occurring during the interval AD 1127–1129 must have been sufficiently intense to produce mid-latitude auroral displays over China and Korea, some of which appeared or extended south of the observing site. This last statement remains true even after proper allowance is made for the fact that during the twelfth century, the north geomagnetic pole was probably situated at the usual high geographic latitude, but in the same geographic longitude range as East Asia. Therefore, it may be inferred that the two series of intense recurrent geomagnetic storms occurred near a medieval maximum in the "eleven-year" solar cycle. Moreover, the overall level of solar activity appears to have been especially high at the end of the second decade of the twelfth century.

    b>Key words. Magnetospheric physics (auroral phenomena; storms and substorms – Solar physics, astrophysics and astronomy (photosphere and chromosphere

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

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


    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

  2. OVATION Prime-2013: Extension of auroral precipitation model to higher disturbance levels

    Newell, P. T.; Liou, K.; Zhang, Y.; Sotirelis, T.; Paxton, L. J.; Mitchell, E. J.


    OVATION Prime (OP) is an auroral precipitation model parameterized by solar wind driving. Distinguishing features of the model include an optimized solar wind-magnetosphere coupling function (dΦMP/dt) which predicts auroral power significantly better than Kp or other traditional parameters, the separation of aurora into categories (diffuse aurora, monoenergetic, broadband, and ion), the inclusion of seasonal variations, and separate parameter fits for each magnetic latitude (MLAT) × magnetic local time (MLT) bin, thus permitting each type of aurora and each location to have differing responses to season and solar wind input—as indeed they do. We here introduce OVATION Prime-2013, an upgrade to the 2010 version currently widely available. The most notable advantage of OP-2013 is that it uses UV images from the GUVI instrument on the satellite TIMED for high disturbance levels (dΦMP/dt > 1.2 MWb/s which roughly corresponds to Kp = 5+ or 6-). The range of validity is approximately 0 power from Polar UVI. Over the common range of validity of OP-2010 and OP-2013, the two models predict auroral power essentially identically, primarily because hemispheric power calculations were done in a way to minimize the impact of OP-2010s noise. To quantitatively demonstrate the improvement at high disturbance levels would require multiple very large substorms, which are rare, and insufficiently present in the limited data set of Polar UVI hemispheric power values. Nonetheless, although OP-2010 breaks down in a variety of ways above Kp = 5+ or 6-, OP-2013 continues to show the auroral oval advancing equatorward, at least to 55° MLAT or a bit less, and OP-2013 does not develop spurious large noise patches. We will also discuss the advantages and disadvantages of other precipitation models more generally, as no one model fits best all possible uses.

  3. Mapping auroral activity with Twitter

    Case, N. A.; MacDonald, E. A.; Heavner, M.; Tapia, A. H.; Lalone, N.


    Twitter is a popular, publicly accessible, social media service that has proven useful in mapping large-scale events in real time. In this study, for the first time, the use of Twitter as a measure of auroral activity is investigated. Peaks in the number of aurora-related tweets are found to frequently coincide with geomagnetic disturbances (detection rate of 91%). Additionally, the number of daily aurora-related tweets is found to strongly correlate with several auroral strength proxies (ravg≈0.7). An examination is made of the bias for location and time of day within Twitter data, and a first-order correction of these effects is presented. Overall, the results suggest that Twitter can provide both specific details about an individual aurora and accurate real-time indication of when, and even from where, an aurora is visible.

  4. On the formation of auroral arcs

    A new mechanism for auroral arc formation is presented. The characteristic linear shape of auroral arcs is determined by magnetically connected plasma clouds in the distant equatorial magnetosphere. These clouds originate as high speed plasma beams in the magnetotail and in the solar wind. It is found that the free energy for driving an auroral arc is provided by the difference of pressure between the cloud and the ambient plasma. (author)

  5. Auroral and photoelectron fluxes in cometary ionospheres

    The analytical yield spectrum method has been used to ascertain photoelectron and auroral electron fluxes in cometary ionospheres, with a view to determining the effects of cometocentric distances, solar zenith angle, and solar minimum and maximum conditions. Auroral electron fluxes are thus calculated for monoenergetic and observed primary electron spectra; auroral electrons are found to make a larger contribution to the observed electron spectrum than EUV-generated photoelectrons. Good agreement is established with extant theoretical works. 55 refs

  6. Interhemispheric contrasts in the ionospheric convection response to changes in the interplanetary magnetic field and substorm activity: a case-study

    B. A. Shand

    Full Text Available Interhemispheric contrasts in the ionospheric convection response to variations of the interplanetary magnetic field (IMF and substorm activity are examined, for an interval observed by the Polar Anglo-American Conjugate Experiment (PACE radar system between ~1600 and ~2100 MLT on 4 March 1992. Representations of the ionospheric convection pattern associated with different orientations and magnitudes of the IMF and nightside driven enhancements of the auroral electrojet are employed to illustrate a possible explanation for the contrast in convection flow response observed in radar data at nominally conjugate points. Ion drift measurements from the Defence Meteorological Satellite Program (DMSP confirm these ionospheric convection flows to be representative for the prevailing IMF orientation and magnitude. The location of the fields of view of the PACE radars with respect to these patterns suggest that the radar backscatter observed in each hemisphere is critically influenced by the position of the ionospheric convection reversal boundary (CRB within the radar field of view and the influence it has on the generation of the irregularities required as scattering targets by high-frequency coherent radar systems. The position of the CRB in each hemisphere is strongly controlled by the relative magnitudes of the IMF Bz and By components, and hence so is the interhemispheric contrast in the radar observations.

    Key words. Magnetospheric physics · Auroral phenomena · Magnetosphere-ionosphere interactions · Storms and substorms

  7. Substorm electric fields in the earth's magnetotail

    A survey has been made of all the electric field data from the University of California, Berkeley, double probe experiment on ISEE-1 (apogee approximately 22 earth radii) during 1980 when the satellite was in the magnetotail. This study was restricted to the 74 events where E cross B flows could be calculated and were equal to or greater than 100 km/s. Substorm times were determined by examining the Ae index for peaks equal to or greater than 250 gamma. In association with substorms, approximately 70 percent of the flows were earthward, and approximately 20 percent had a signature called near satellite reconnection (first described by Nishida et al. (1983) of tailward flow followed by earthward flow which can be interpreted in terms of a model where the x-line forms earthward of the satellite and subsequently propagates tailward of X(GSM) = -21 earth radii and within the absolute value of Y(GSM) equal to or less than 4.5 earth radii. These data suggest that the near earth x-line usually forms tailward of X(GSM) approximately -20 earth radii. 17 references

  8. Substorm morphology of >100 keV protons

    The latitudinal morphology of >100 keV protons at different local times has been studied as a function of substorm activity Acharacteristic pattern has been found: During quiet times there is an isotropic zone centered around 670 near midnight, but located on higher latitudes towards dusk and dawn. This zone moves slightly equatorward during the substorm growth phase. During the expansive phase the precipitation spreads poleward apparently to approximately 710 near midnight. The protons are precipitated over a large local time interval on the night side, but the most intense fluxes are found in the pre-midnight sector. A further poleward expansion, to more than 750 near midnight, seems to take place late in the substorm. Away from midnight the expansion reaches even higher latitudes. During the recovery phase the intensity of the expanded region decreases gradually; the poleward boundary is almost stationary if the interplanetary magnetic field has a northward component and no further substorm activity takes place. Mainly protons with energy below approximately 500 keV are precipitated in the expanded region. On the dayside no increase in the precipitation rates is found during substorm expansion, but late in the substorm an enhanced precipitation is found, covering several degrees of latitude. The low-latitude anisotropic precipitation zone is remarkably stable during substorms. A schematic model is presented and discussed in relation to earlier results. (Auth.)

  9. A comparison of the probability distribution of observed substorm magnitude with that predicted by a minimal substorm model

    S. K. Morley


    Full Text Available We compare the probability distributions of substorm magnetic bay magnitudes from observations and a minimal substorm model. The observed distribution was derived previously and independently using the IL index from the IMAGE magnetometer network. The model distribution is derived from a synthetic AL index time series created using real solar wind data and a minimal substorm model, which was previously shown to reproduce observed substorm waiting times. There are two free parameters in the model which scale the contributions to AL from the directly-driven DP2 electrojet and loading-unloading DP1 electrojet, respectively. In a limited region of the 2-D parameter space of the model, the probability distribution of modelled substorm bay magnitudes is not significantly different to the observed distribution. The ranges of the two parameters giving acceptable (95% confidence level agreement are consistent with expectations using results from other studies. The approximately linear relationship between the two free parameters over these ranges implies that the substorm magnitude simply scales linearly with the solar wind power input at the time of substorm onset.

  10. Nuclear magnetohydrodynamic EMP, solar storms, and substorms

    In addition to a fast electromagnetic pulse (EMP), a high altitude nuclear burst produces a relatively slow magnetohydrodynamic EMP (MHD EMP), whose effects are like those from solar storm geomagnetically induced currents (SS-GIC). The MHD EMP electric field E approx-lt 10-1 V/m and lasts approx-lt 102 sec, whereas for solar storms E approx-gt 10-2 V/m and lasts approx-gt 103 sec. Although the solar storm electric field is lower than MHD EMP, the solar storm effects are generally greater due to their much longer duration. Substorms produce much smaller effects than SS-GIC, but occur much more frequently. This paper describes the physics of such geomagnetic disturbances and analyzes their effects

  11. Advanced Stellar Compass Summary for the Auroral Lites mission

    Jørgensen, John Leif


    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....

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

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


    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.

  13. Turbulent acceleration of auroral electrons

    It is shown that the characteristic peak in the auroral electron velocity distribution can be generated stochastically through resonant interactions with lower-hybrid electrostatic turbulence. The peak itself is shown to be a direct consequence of restrictions imposed on reflexion of electron velocities in the frame of reference of individual wave packets by the limitation in group velocity. A Monte-Carlo model demonstrates how the various properties of the acceleration region are reflected in the resultant electron distribution. It is shown, in particular, that the width of the peak is governed by the amplitude of the turbulence, while the amplitude of the peak reflects the column density of wave energy. Electron distributions encountered within three auroral arcs are interpreted to yield order of magnitude estimates of the amplitude and rms electric field of lower-hybrid wave packets. The velocities and frequencies of the resonant waves, the net electric field, the column density of wave energy and the electric-field energy density are also estimated. The results are found to be consistent with available electric-field measurements. A general broadening of the electron distribution caused by less systematic interactions between electrons and wave packets is shown to have a negligible effect on the peak resulting from the reflexion process; it does, though, lead to the creation of a characteristic high-energy tail. (author)

  14. Storm/substorm signatures in the outer belt

    The response of the ring current region is compared for periods of storm and substorm activity, with an attempt to isolate the contributions of both processes. The authors investigate CRRES particle data in an overview format that allows the display of long-term variations of the outer radiation belt. They compare the evolution of the ring current population to indicators of storm (Dst) and substorm (AE) activity and examine compositional changes. Substorm activity leads to the intensification of the ring current at higher L (L ∼ 6) and lower ring current energies compared to storms (L ∼ 4). The O+/H+ ratio during substorms remains low, near 10%, but is much enhanced during storms (can exceed 100%). They conclude that repeated substorms with an AE ∼ 900 nT lead to a ΔDst of ∼ 30 nT, but do not contribute to Dst during storm main phase as substorm injections do not form a symmetric ring current during such disturbed times

  15. Auroral and magnetic variations in the polar cusp and cleft. Signatures of magnetopause boundary layer dynamics

    By combining continous ground-based observations of polar cleft/cusp auroras and local magnetic variations with electromagnetic parameters obtained from satellites in polar orbit (low-altitude cleft/cusp) and in the magnetosheath/interplanetary space, different electrodynamic processes in the polar cleft/cusp have been investigated. One of the more controversial questions in this field is related to the observed shifts in latitude of cleft/cusp auroras and the relationships with the interplanetary magnetic field (IMF) orientation, local magnetic disturbances (DP2 and DPY modes) and magnetospheric substorms. A new approach which may contribute to clarifying these complicated relationships, simultaneous groundbased observations of the midday and evening-midnight sectors of the auroral oval, is illustrated. A related topic is the spatial relationship between the cleft/cusp auroras and the ionospheric convection currents. A characteristic feature of the polar cusp and cleft regions during negative IMF Bz is repeated occurrence of certain short-lived auroral structures moving in accordance with the local convection pattern. Satellite measurements of particle precipitation, magnetic field and ion drift components permit detailed investigations of the electrodynamics of these cusp/cleft structures. Information on electric field components, Birkeland currents, Poynting flux, height-integrated Pedersen conductivity and Joule heat dissipation rate has been derived. These observations are discussed in relation to existing models of temporal plasma injections from the magnetosheath

  16. Estimates of the field-aligned current density in current-carrying filaments using auroral zone ground-based observations

    M. A. Danielides

    Full Text Available We described the ground signatures of dynamic substorm features as observed by the imaging riometer, magnetometers and all-sky camera (ASC at Kilpisjärvi, Finland on 5 and 25 October 1999 during the late evening hours. The magnetometer data was consistent with the motion of up-ward field-aligned currents (FACs associated with absorption patches moving within the field of view of the riometer. We used riometer data in order to estimate the intensity of FACs associated with these local current-carrying filaments. It is shown that during these events, the estimated FAC intensity exceeds a threshold value that corresponds to the excitation of the low-frequency turbulence in the upper ionosphere. As a result, a quasi-oscillating regime of anomalous resistivity on the auroral field lines can give rise to the burst-like electron acceleration responsible for simultaneously observed auroral forms and bursts of Pi1B pulsations.

    Key words. Ionosphere (active experiments; auroral ionosphere; electric fields and currents

  17. Statistical analysis of extreme auroral electrojet indices

    Nakamura, Masao; Yoneda, Asato; Oda, Mitsunobu; Tsubouchi, Ken


    Extreme auroral electrojet activities can damage electrical power grids due to large induced currents in the Earth, degrade radio communications and navigation systems due to the ionospheric disturbances and cause polar-orbiting satellite anomalies due to the enhanced auroral electron precipitation. Statistical estimation of extreme auroral electrojet activities is an important factor in space weather research. For this estimation, we utilize extreme value theory (EVT), which focuses on the statistical behavior in the tail of a distribution. As a measure of auroral electrojet activities, auroral electrojet indices AL, AU, and AE, are used, which describe the maximum current strength of the westward and eastward auroral electrojets and the sum of the two oppositely directed in the auroral latitude ionosphere, respectively. We provide statistical evidence for finite upper limits to AL and AU and estimate the annual expected number and probable intensity of their extreme events. We detect two different types of extreme AE events; therefore, application of the appropriate EVT analysis to AE is difficult.

  18. Waterhole: An auroral-ionosphere perturbation experiment

    Whalen, B. A.; Yau, A. W.; Creutzberg, F.; Pongratz, M. B.

    A sounding rocket carrying 100 kg of high explosives and plasma diagnostic instrumentation was launched from Churchill Research Range on 6 April 1980 over a premidnight auroral arc. The object of the experiment was to produce an ionospheric hole or plasma density depletion at about 300 km altitude on field lines connected to an auroral arc. The plasma depletion is produced when the explosive by-products (mostly water) charge-exchange with the ambient O+ ions and then rapidly recombine. It was speculated that the presence of the "hole" would interfere with the field-aligned current systems associated with the arc and would in turn perturb the auroral source mechanism. The release occurred about 10 km poleward of the auroral arc fieldlines. As expected, a large ionospheric hole was detected by rocket-borne plasma sensors. Within a few seconds following the release (a) the energetic electron precipitation observed in the hole dropped to background levels, (b) the luminosity of the auroral arc observed by a ground-based auroral scanning photometer decreased by a factor of two, and (c) the ionospheric E region density below the hole decayed at a rate consistent with a sudden reduction in particle precipitation. The simultaneous onset of these gross changes in electron precipitation coincident with the release strongly suggests a cause and effect relationship. In particular, these results suggest that the ionospheric plasma and the field-aligned current systems play a crucial role in the auroral acceleration process.

  19. Auroral Phenomena in Brown Dwarf Atmospheres

    Pineda, J. Sebastian; Hallinan, Gregg


    Since the unexpected discovery of radio emission from brown dwarfs some 15 years ago, investigations into the nature of this emission have revealed that, despite their cool and neutral atmospheres, brown dwarfs harbor strong kG magnetic fields, but unlike the warmer stellar objects, they generate highly circularly polarized auroral radio emission, like the giant planets of the Solar System. Our recent results from Keck LRIS monitoring of the brown dwarf LSR1835+32 definitively confirm this picture by connecting the auroral radio emission to spectroscopic variability at optical wavelengths as coherent manifestations of strong large-scale magnetospheric auroral current systems. I present some of the results of my dissertation work to understand the nature brown dwarf auroral phenomena. My efforts include a survey of Late L dwarfs and T dwarfs, looking for auroral Hα emission and a concurrent survey looking for the auroral emission of H3+ from brown dwarfs with radio pulse detections. I discuss the potential connection of this auroral activity to brown dwarf weather phenomena and how brown dwarf aurorae may differ from the analogous emission of the magnetized giant planets in the Solar System.

  20. Measurements of auroral particles by means of sounding rockets of mother-daughter type

    The scientific objective of the S17 payloads was to study the ionosphere during auroral situations and especially with regards to the local fine structure and a possible separation of spatial and temporal variations of auroral phenomena. The intensities of 8 keV and 2 keV electrons have been measured from one sounding rocket launched into a breakup aurora of moderate activity and from another rocket launched into a very active substorm situation. Both the rockets were of mother-daughter type i.e. had two separated payloads. The general features in the data of different particle energies were very similar over the whole flight time of the rockets. Special events and gradients and well identifiable shapes in the particle intensities were studied to see if the intensity fluctuations obtained from two detectors in one payload or from detectors into separate payloads were time delayed. Such time delays in the particle flux intensities were obvious in both of the rocket measurements and most of these time shifts could be understood as caused by spatial variations in the particle precipitation. In parts of the rocket flights the particle intensity variations were true temporal changes. The time lags between 8 keV and 2 keV electron intensities detected in the same payload, which could be observed and were obtained by crosscorrelation analyses, were in the range less than 0.3 s and most of them less than 0.1 s. If the time differences are assumed to be caused by the velocity dispersion of the particles, the particle data reported here placed the modulation source at a distance of less than 10 000 km from the rocket position. Measurements at the S17-1 mother payload of the electric field have been compared with data of precipitating electrons and low-light-level-TV-recording of the auroral situation. An inverted-V precipitation event was observed and was associated with auroral arcs and with reversals of the measured electric field components implicating the possibility of

  1. Combined optical, EISCAT and magnetic observations of the omega bands/Ps6 pulsations and an auroral torch in the late morning hours: a case study

    V. Safargaleev


    Full Text Available We present here the results of multi-instrument observations of auroral torch and Ps6 magnetic pulsations, which are assumed to be the magnetic signature of the spatially periodic optical auroras known as omega bands. Data from TV and ASC cameras in Barentsburg and Ny Ålesund, EISCAT radars in Longyearbyen and Tromsø, as well as IMAGE network were used in this study. The auroral phenomenon which was considered differed from that previously discussed, as it occurred both in an unusual place (high latitudes and at an unusual time (late morning hours. We show that this might occur due to specific conditions in the interplanetary medium, causing the appropriate deformation of the magnetosphere. In such a case, the IMF turned out to be an additional factor in driving the regime of Ps6/omega bands, namely, only by acting together could a substorm onset in the night sector and Bz variations result in their generation. Since the presumable source of Ps6/omega bands does not co-locate with convection reversal boundaries, we suggest the interpretation of the phenomena in the frame of the interchange instability instead of the Kelvin-Helmholtz instability that is widely discussed in the literature in connection with omega auroras. Some numerical characteristics of the auroral torch were obtained. We also emphasize to the dark hole in the background luminosity and the short-lived azimuthally-restricted auroral arc, since their appearance could initiate the auroral torch development.

    Keywords. Magnetospheric physics (Auroral phenomena; Plasma convection; Solar wind-magnetosphere interaction

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

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


    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. Auroral Morphologies of Jupiter and Saturn

    Grodent, Denis


    We review the principal differences and similarities of the morphologies of Jupiter and Saturn's auroral emissions. We then show some examples of UV images that are expected to be acquired with Cassini UVIS at Saturn and Juno UVS at Jupiter.

  4. Auroral electrodynamics of plasma boundary regions

    Liléo, Sónia


    The electrodynamic coupling between the auroral ionosphere and the magnetosphere is the main subject of this thesis. Satellite measurements of electric and magnetic fields and of charged particles are used to explore three distinct plasma boundaries, magnetically linked to the nightside auroral ionosphere. These boundaries are the inner edge of the plasma sheet (PS), and the inner and the outer edges of the plasma sheet boundary layer (PSBL). Strong ionospheric electric fields with amplitudes...

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

    C. Forsyth


    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.

  6. Indications for ionospheric participation in the substorm process from AMPTE/CCE observations

    The authors present and discuss observations with the AMPTE/CCE spacecraft in the near-earth nightside magnetosphere, which show a significant enhancement of ionospheric particle presence (mainly O+) at the beginning of the substorm growth phase. Such an enhancement indicates not only an ionospheric participation in the substorm initiation, but also an active role in the substorm growth phase

  7. Indications for ionospheric participation in the substorm process from AMPTE/CCE observations. [Charge Composition Explorer

    Daglis, I. A.; Sarris, E. T.; Kremser, G.


    Observations with the AMPTE/CCE spacecraft in the near-earth nightside magnetosphere show a significant enhancement of ionospheric particle presence, mainly O(+), at the beginning of the substorm growth phase. Such an enhancement indicates not only an ionospheric participation in the substorm initiation, but also an active role in the substorm growth phase.

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

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


    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.

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

    N. A. Zolotukhina


    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.

  10. Origins of the Earth's Diffuse Auroral Precipitation

    Ni, Binbin; Thorne, Richard M.; Zhang, Xiaojia; Bortnik, Jacob; Pu, Zuyin; Xie, Lun; Hu, Ze-jun; Han, Desheng; Shi, Run; Zhou, Chen; Gu, Xudong


    The Earth's diffuse auroral precipitation provides the major source of energy input into the nightside upper atmosphere and acts as an essential linkage of the magnetosphere-ionosphere coupling. Resonant wave-particle interactions play a dominant role in the scattering of injected plasma sheet electrons, leading to the diffuse auroral precipitation. We review the recent advances in understanding the origin of the diffuse aurora and in quantifying the exact roles of various magnetospheric waves in producing the global distribution of diffuse auroral precipitation and its variability with the geomagnetic activity. Combined scattering by upper-and lower-band chorus accounts for the most intense inner magnetospheric electron diffuse auroral precipitation on the nightside. Dayside chorus can be responsible for the weaker dayside electron diffuse auroral precipitation. Pulsating auroras, the dynamic auroral structures embedded in the diffuse aurora, can be mainly caused by modulation of the excitation of lower band chorus due to macroscopic density variations in the magnetosphere. Electrostatic electron cyclotron harmonic waves are an important or even dominant cause for the nightside electron diffuse auroral precipitation beyond {˜}8Re and can also contribute to the occurrence of the pulsating aurora at high L-shells. Scattering by electromagnetic ion cyclotron waves could quite possibly be the leading candidate responsible for the ion precipitation (especially the reversed-type events of the energy-latitude dispersion) in the regions of the central plasma sheet and ring current. We conclude the review with a summary of current understanding, outstanding questions, and a number of suggestions for future research.

  11. Origins of the Earth's Diffuse Auroral Precipitation

    Ni, Binbin; Thorne, Richard M.; Zhang, Xiaojia; Bortnik, Jacob; Pu, Zuyin; Xie, Lun; Hu, Ze-jun; Han, Desheng; Shi, Run; Zhou, Chen; Gu, Xudong


    The Earth's diffuse auroral precipitation provides the major source of energy input into the nightside upper atmosphere and acts as an essential linkage of the magnetosphere-ionosphere coupling. Resonant wave-particle interactions play a dominant role in the scattering of injected plasma sheet electrons, leading to the diffuse auroral precipitation. We review the recent advances in understanding the origin of the diffuse aurora and in quantifying the exact roles of various magnetospheric waves in producing the global distribution of diffuse auroral precipitation and its variability with the geomagnetic activity. Combined scattering by upper-and lower-band chorus accounts for the most intense inner magnetospheric electron diffuse auroral precipitation on the nightside. Dayside chorus can be responsible for the weaker dayside electron diffuse auroral precipitation. Pulsating auroras, the dynamic auroral structures embedded in the diffuse aurora, can be mainly caused by modulation of the excitation of lower band chorus due to macroscopic density variations in the magnetosphere. Electrostatic electron cyclotron harmonic waves are an important or even dominant cause for the nightside electron diffuse auroral precipitation beyond {˜}8Re and can also contribute to the occurrence of the pulsating aurora at high L-shells. Scattering by electromagnetic ion cyclotron waves could quite possibly be the leading candidate responsible for the ion precipitation (especially the reversed-type events of the energy-latitude dispersion) in the regions of the central plasma sheet and ring current. We conclude the review with a summary of current understanding, outstanding questions, and a number of suggestions for future research.

  12. Auroral pulsations and accompanying VLF emissions

    V. R. Tagirov

    Full Text Available Results of simultaneous TV observations of pulsating auroral patches and ELF-VLF-emissions in the morning sector carried out in Sodankylä (Finland on February 15, 1991 are presented. Auroral pulsating activity was typical having pulsating patches with characteristic periods of about 7 s. Narrow-band hiss emissions and chorus elements at intervals of 0.3–0.4 s formed the main ELF-VLF activity in the frequency range 1.0–2.5 kHz at the same time. The analysis of auroral images with time resolution of 0.04 s allowed perfectly separate analysis of spatial and temporal variations in the auroral luminosity. Mutual correspondence between the behaviour of the luminous auroral patches and the appearance of ELF noise type hiss emissions and VLF chorus trains was found in two intervals chosen for analysis. While the hiss emissions were associated with the appearance of luminosity inside a limited area close to the zenith, the structured VLF emissions were accompanied by rapid motion of luminosity inside the area. The spatial dimension of the pulsating area was about 45–50 km and luminosity propagated inside it with velocity of about 10–12 kms. We discuss a new approach to explain the 5–15 s auroral pulsation based on the theory of flowing cyclotron maser and relaxation characteristics of ionosphere.

    Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions · Space plasma physics (wave-particle interactions

  13. The Lewis Research Center geomagnetic substorm simulation facility

    Berkopec, F. D.; Stevens, N. J.; Sturman, J. C.


    A simulation facility was established to determine the response of typical spacecraft materials to the geomagnetic substorm environment and to evaluate instrumentation that will be used to monitor spacecraft system response to this environment. Space environment conditions simulated include the thermal-vacuum conditions of space, solar simulation, geomagnetic substorm electron fluxes and energies, and the low energy plasma environment. Measurements for spacecraft material tests include sample currents, sample surface potentials, and the cumulative number of discharges. Discharge transients are measured by means of current probes and oscilloscopes and are verified by a photomultiplier. Details of this facility and typical operating procedures are presented.

  14. Ring current and auroral electrojets in connection with interplanetary medium parameters during magnetic storm

    Y. I. Feldstein

    Full Text Available The relationship between the auroral electrojet indices (AE and the ring current magnetic field (DR was investigated by observations obtained during the magnetic storm on 1-3 April 1973. During the storm main phase the DR development is accompanied by a shift of the auroral electrojets toward the equator. As a result, the standard AE indices calculated on the basis of data from auroral observatories was substantially lower than the real values (AE'. To determine AE' during the course of a storm main phase data from subauroral magnetic observatories should be used. It is shown that the intensity of the indices (AE' which take into account the shift of the electrojets is increased substantially relative to the standard indices during the storm main phase. AE' values are closely correlated with geoeffective solar wind parameters. A high correlation was obtained between AE' and the energy flux into the ring current during the storm main phase. Analysis of magnetic field variations during intervals with intense southward IMF components demonstrates a decrease of the saturation effect of auroral electrojet currents if subauroral stations magnetic field variations are taken into account. This applies both to case studies and statistical data. The dynamics of the electrojets in connection with the development of the ring current and of magnetospheric substorms can be described by the presence (absence of saturation for minimum (maximum AE index values during a 1-h interval. The ring current magnetic field asymmetry (ASY was calculated as the difference between the maximum and minimum field values along a parallel of latitude at low latitudes. The ASY value is closely correlated with geoeffective solar wind parameters and simultaneously is a more sensitive indicator of IMF Bz variations than the symmetric ring current.

  15. The Auroral Zone: A citizen science project to classify auroral imaging data

    Chaddock, D.; Spanswick, E.; Gillies, D. M.; Quinney, A.; Donovan, E.; Murray, M. S.


    Currently, over 40 million images of the aurora have been recorded by University of Calgary all-sky imagers. Analysis of these images is an important and crucial step in the advancement of auroral physics. The number of images waiting to be analyzed is expected to increase dramatically with the introduction of TREx (Transition Region Explorer), a new high resolution imaging network set to be deployed in late 2016. In order to classify large amounts of images in a short period of time, we have designed a citizen science project aimed at engaging the general public in auroral science, called "The Auroral Zone". This project facilitates a symbiotic relationship between the scientific community and the general public. Using the data from this website, a large database of classified auroral images will be created and then used for future analysis by the scientific community. In exchange, the general public can learn about the aurora and contribute to auroral physics in a tangible way. The ultimate aim of this project is to create an ever expanding database of all-sky images classified by arc type (i.e. single arc, diffuse aurora, multiple arc, etc.) and filtered for adverse viewing conditions (i.e. snow, rain, light pollution, etc). We aim to introduce "The Auroral Zone" into the school systems to interest young scientists in the spectacular natural phenomenon that defines the Canadian North. "The Auroral Zone" is a collaborative project between the University of Calgary, Canadian Space Agency, AuroraMAX, and Aurorasaurus.

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

    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...

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

    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...

  18. Dayside cosmic noise absorption at the equatorward boundary of auroral oval as observed from Maitri, Antarctica (L = 5; CGM 62.45°S, 55.45°E)

    Behera, Jayanta K.; Sinha, Ashwini K.; Vichare, Geeta; Kozyreva, Olga; Rawat, Rahul; Dhar, Ajay


    On 02 April 2011, a couple of cosmic noise absorption (CNA) events were detected at Maitri, Antarctica (L = 5; CGM 63.14°S, 53.69°E) confining to nighttime and daytime. One of the two events that occurred during night hours was caused due to auroral substorm onset. The current study focuses on the later CNA event, which was recorded during daytime (10:00-13:00 magnetic local time (MLT), MLT = UT-1, at Maitri, Antarctica). We refer to this CNA event as dayside CNA (DCNA) event. Absence of westward electrojet during DCNA confirms its dissimilarity from auroral substorm absorption events. A comparison has been made between the DCNA event of 02 April 2011 with that of 14 July 2011, a day with substorm activity when Maitri is in dayside but without DCNA event. The comparison has been made in the light of interplanetary conditions, imaging riometer data, ground magnetic signatures, GOES electron flux density, and associated pulsations. The study shows that stronger prolonged eastward interplanetary electric field favors the occurrence of DCNA event. It is concluded that DCNA event is due to the gradient curvature drift of trapped nonrelativistic electrons in the equatorial plane. Estimated energy of trapped electrons using azimuthal drift time for a set of ground stations within the auroral oval confirms the enhancement in electron fluxes in the same energy band as recorded by geostationary satellites GOES 13 and GOES 15. The reason for precipitation of electrons is expected to be the loss cone scattering caused by wave-particle interaction triggered by ULF waves.

  19. Two types of ion energy dispersions observed in the nightside auroral regions during geomagnetically disturbed periods

    Hirahara, M.; Mukai, T.; Nagai, T.; Kaya, N.; Hayakawa, H.; Fukunishi, H.


    The Akebono satellite has observed two types of energy dispersion signatures of discrete ion precipitation event in the nightside auroral regions during active geomagnetic conditions. The charged particle experiments and electric and magnetic field detectors on board Akebono provide us with essential clues to characterize the source regions and acceleration and/or injection processes associated with these two types of ion signatures. The magnetic field data obtained simultaneously by the geosynchronous GOES 6 and 7 satellites and the ground magnetograms are useful to examine their relationships with geomagnetic activity. Mass composition data and pitch angle distributions show that different sources and processes should be attributed to two types (Types I and II) of energy dispersion phenomena. Type I consists of multiple bouncing ion clusters constituted by H+. These H+ clusters tend to be detected at the expansion phase of substorms and have characteristic multiple energy-dispersed signatures. Type II consists of O+ energy dispersion(s), which is often observed at the recovery phase. It is reasonable to consider that the H+ clusters of Type I are accelerated by dipolarization at the equator, are injected in the field-aligned direction, and bounce on closed field lines after the substorm onset. We interpret these multiple energy dispersion events as mainly due to the time-of-flight (TOF) effect, although the convection may influence the energy-dispersed traces. Based of the TOF model, we estimate the source distance to be 20-30 RE along the field lines. On the other hand, the O+ energy dispersion of Type II is a consequence of reprecipitation of terrestrial ions ejected as an upward flowing ion (UFI) beam from the upper ionosphere by a parallel electrostatic potential difference. The O+ energy dispersion is induced by the E×B drift during the field-aligned transport from the source region to the observation point.

  20. Fine scale structures of pulsating auroras in the early recovery phase of substorm using ground-based EMCCD camera

    Nishiyama, Takanori; Sakanoi, Takeshi; Miyoshi, Yoshizumi; Kataoka, Ryuho; Hampton, Donald; Katoh, Yuto; Asamura, Kazushi; Okano, Shoichi


    We have carried out ground-based observations, optimized to temporal and spatial characteristics of pulsating auroras (PAs) in the micro/meso scale, using an electron multiplying charge coupled device (EMCCD) camera with a wide field of view corresponding to 100 × 100 km at an altitude of 110 km and a high sampling rate up to 100 frames per second. We focus on transient PAs propagating southward around 1100 UT, in the early recovery phase of the substorm, on 4th March 2011. Three independent patches (PA1-3) each with different periods between 4 and 7 s were observed, which means that the periodicity was not explained by the electron bounce motion and strongly depended on local plasma conditions in the magnetosphere or in the ionosphere. One more insight is that only PA1 had also a sharp peak of modulations around 1.5 Hz, with a narrow frequency width of 0.30 Hz, and the strong modulations existed as a small spot in the center of PA1. We have also conducted cross spectrum analysis and have obtained coherence and phase distributions for auroral variations between 0.1 and 3.0 Hz. The results indicated that low frequency variations from 0.2 to 0.5 Hz inside PA1-3 propagated as a collective motion in well-defined directions. The estimated horizontal propagation velocities ranged from 50 to 120 km/s at the auroral altitude. The velocities are almost consistent with the Alfven speed at the magnetic equator, which suggests that compressional waves have an effect on PA via modulations of the ambient plasma environment.

  1. Theoretical magnetograms based on quantitative simulation of a magnetospheric substorm

    Using substorm currents derived from the Rice computer simulation of the substorm event of September 19, 1976, we have computed theoretical magnetograms as a function of universal time for various stations. A theoretical Dst has also been computed. Our computed magnetograms were obtained by integrating the Biot-Savart law over a maze of approximately 2700 wires and bands that carry the ring currents, the Birkeland currents, and the horizontal ionospheric currents. Ground currents and dynamo currents were neglected. Computed contributions to the magnetic field perturbation from eleven different kinds of currents are displayed (e.g., ring currents, northern hemisphere Birkeland currents). First, overall agreement of theory and data is generally satisfactory, especially for stations at high and mid-magnetic latitudes. Second, model results suggest that the ground magnetic field perturbations arise from very complicated combinations of different kinds of currents and that the magnetic field disturbances due to different but related currents often cancel each other, despite the fact that complicated inhomogeneous conductivities in our model prevent rigorous application of Fukushima's theorem. Third, both the theoretical and observed Dst decrease during the expansion phase of the substorm, but data indicate that Dst relaxes back toward its initial value within about an hour after the peak of the substorm. Fourth, the dawn-dusk asymmetry in the horizontal component of magnetic field disturbance at low latitudes in a substorm is essentially due to a net downward Birkeland current at noon, net upward current at midnight, and generally antisunward flowing electrojets; it is not due to a physical partial ring current injected into the duskside of the inner magnetosphere

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

    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...

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

    T. Karlsson


    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.

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

    O. Marghitu


    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.

  5. Dynamics of the inner magnetosphere near times of substorm onsets

    Maynard, N. C.; Burke, W. J.; Basinska, E. M.; Erickson, G. M.; Hughes, W. J.; Singer, H. J.; Yahnin, A. G.; Hardy, D. A.; Mozer, F. S.


    The electrodynamics of the inner magnetosphere near times of substorm onsets have been investigated using CRRES measurements of magnetic and electric fields, energetic electron fluxes, in conjunction with ground-based observations. Six events were studied in detail, spanning the 2100 to 0000 MLT sector and L values from 5 to 7. In each case the dawn-dusk electric field was enhanced over typical background electric fields, and significant, low-frequency pulsation activity was observed. The amplitudes of the pulsations were larger than the background electric fields. Dusk-dawn excursions of the cross-tail electric field often correlated with changes in currents and particle energies at CRRES and with ULF wave activity observed on the ground. Variations of the electric field and Poynting vectors with periods in the Pi 2 range are consistent with bouncing Alfvén waves that provide electromagnetic communication between the ionosphere and plasma sheet. Magnetic signatures of field-aligned current filaments directed away from the ionosphere, presumably associated with the substorm current wedge, were observed during three orbits. In all cases, ground signatures of substorm expansion were observed at least 5 min before the injection of electrons at CRRES. Field-aligned fluxes of counter-streaming, low-energy electrons were detected after three of the injections. We develop an empirical scenario for substorm onset. The process grows from ripples at the inner edge of the plasma sheet associated with dusk-dawn excursions of the electric field, prior to the beginning of dipolarization. Energy derived from the braking of the inward plasma convection flows into the ionosphere in the form of Poynting flux. Subsequently reflected Poynting flux plays a crucial role in the magnetosphere-ionosphere coupling. Substorms develop when significant energy (positive feedback?) flows in both directions, with the second cycle stronger than the initial. Pseudobreakups occur when energy flow

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

    Paul Prikryl


    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.

  7. Investigation of magnetospheric-ionospheric current systems realized the solar wind energy during a substorm

    Methods for quantitative description of spatial distribution of electrical field and currents in high-altitude ionosphere according to satellite, radar and geomagnetic data during substorms are analyzed. Dependence of existing physical models of substorm processes in geomagnetosphere on methods of experimental data processing is discussed. New current system is proposed for explanation of electrical field and currents behaviour in polar ionosphere during substorm without assumption on instability and recoupling in plasma layer of magnetosphere tail. Refs. 18, refs. 3

  8. Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

    Liu, Jun-Ming; Zhang, Bei-Chen; Kamide, Y.; Wu, Zhen-Sen; Hu, Ze-Jun; Yang, Hui-Gen


    An attempt is made to study the difference, if any, between the response of the polar ionosphere to spontaneous substorms and that to trigger-associated substorms in terms of electrodynamic parameters including ionospheric current vectors, the electric potential, and the current function. The results show that, in the first approximation, the ionospheric parameters for the two types of substorms are quite similar. It is therefore conceived that spontaneous substorms are not very different from trigger-associated substorms in the development of substorm processes in the magnetosphere-ionosphere system. We demonstrate, however, that spontaneous substorms seem to have a more clearly identifiable growth phase, whereas trigger-associated substorms have a more powerful unloading process. Changes in the current intensity and the electric potential drop across the polar cap in the recovery phase are also quite different from each other. Both the current intensity and the cross-polar cap potential drop show a larger decrease in the recovery phase of trigger-associated substorms, but the potential drop decreases only slightly and the currents in the late morning sector are still strong for spontaneous substorms. We interpret these findings as an indication of the relative importance of the unloading process and the directly driven process in conjunction with the north-south polarity of the interplanetary magnetic field. There still exists a strong directly driven process in the recovery phase of spontaneous substorms. For trigger-associated substorms, however, both the directly driven process and the unloading process become weak after the peak time.

  9. The effect of variations of the solar wind energy input on the disturbance onsets in the magnetotail during substorms

    Lin, N.; Frey, H. U.; Mende, S. B.; Mozer, F. S.; Lysak, R. L.; Song, Y.; Angelopoulos, V.


    We have examined the relationships between disturbance onsets in the magnetotail and the corresponding variations of the solar wind energy input within 1 hour prior and after the times of the space onsets. The space disturbances examined include dipolarization signatures, intensification of magnetic field fluctuations, and sudden occurrences of plasma flows, which are associated with auroral substorm events. The solar wind energy input rate is calculated as the ɛ coupling function [Perreault and Akasofu, 1978]. To remove short time scale variations of the solar wind we have taken three minute integration of ɛ as the measurements of the solar wind energy input. A total of 77 space events are surveyed. We found that prior to the occurrences of the space disturbance onsets the solar wind energy input may reach a maximum value which is enough to power an auroral substorm (corresponding to ɛ >10^11 J/s). Most of the space onsets (~ 90%) occurred during the decrease of the solar wind energy input. The reduction period has no dependence on the location where the space onsets occurred. The amount of energy reduction seems to increase with the maximum energy input level before the onsets. The above findings may be understood in terms of the interaction between the solar wind and the magnetosphere. The transfer of the solar wind energy and momentum is the results of nonlinear Alfvénic interactions between fast mode waves and the current sheets throughout the magnetopause and in the tail. A net momentum transport in the tangential direction across the magnetopause provides electromagnetic viscous-like drag force and stretches the magnetotail. The drag force tends to be balanced by the resultant force of JxB and -grad_P(thermal) forces acting on the magnetotail, which is directed earthward. The reduction of the solar wind momentum input breaks the force balance on the stressed magnetotail and provides favorable conditions for the excitation and intensification of

  10. From the Solar Wind to the Magnetospheric Substorm

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


    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.

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

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


    @@ 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.

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

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


    substorm intensification at similar to 0154 UT sit a local time spatially separated from the initial substorm activity region. During this event, both Geotail and IMP-8 were in the mid-tail near the midnight meridian (Geotail (X, Y) approximate to (-30,-3)R-E and IMP-8 (X,Y) approximate to (-37,2)R......-E). Observations indicated that the substorm onset activity was localized in the postmidnight region. After the onset, Geotail detected a transient dipolarization which was not accompanied by large plasma flows (i.e., \\ V-x \\less than or equal to 200 km/s). The subsequent substorm intensification produced enduring...

  13. EEJ and EIA variations during modeling substorms with different onset moments

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


    This paper presents the simulations of four modeling substorms with different moment of substorm onset at 00:00 UT, 06:00 UT, 12:00 UT, and 18:00 UT for spring equinoctial conditions in solar activity minimum. Such investigation provides opportunity to examine the longitudinal dependence of ionospheric response to geomagnetic substorms. Model runs were performed using modified Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP). We analyzed GSM TIP simulated global distributions of foF2, low latitude electric field and ionospheric currents at geomagnetic equator and their disturbances at different UT moments substorms. We considered in more detail the variations in equatorial ionization anomaly, equatorial electrojet and counter equatorial electrojet during substorms. It is shown that: (1) the effects in EIA, EEJ and CEJ strongly depend on the substorm onset moment; (2) disturbances in equatorial zonal current density during substorm has significant longitudinal dependence; (3) the observed controversy on the equatorial ionospheric electric field signature of substorms can depend on the substorm onset moments, i.e., on the longitudinal variability in parameters of the thermosphere-ionosphere system.

  14. Dynamic substorm injections - similar magnetospheric phenomena at earth and Mercury

    Correlations between energetic electrons, plasma electrons, and magnetic fields during the Mercury 1 energetic particle events are examined and comparisons are made with several well-documented substorm injections at the earth. The data reveal that the B and B-prime events possess the same characteristics as single-point observations of terrestrial dynamic injections. Several recently discovered correlations between the energetic electrons, plasma electrons, and magnetic fields at Mercury are discussed. 22 references

  15. Calibrating a Magnetotail Model for Storm/Substorm Forecasting

    Horton, W.; Siebert, S.; Mithaiwala, M.; Doxas, I.


    The physics network model called WINDMI for the solar WIND driven Magnetosphere-Ionosphere weather system is calibrated on substorm databases [1] using a genetic algorithm. We report on the use of the network as a digital filter to classify the substorms into three types; a process traditionally performed individual inspection. We then turn to using the filter on the seven Geospace Environmental Modeling (GEM) Storms designated for community wide study. These storms cover periods of days and contain many substorms. First the WINDMI model is run with the 14 parameters set from the study based on the Blanchard-McPherron database of 117 isolated substorms with 80% of the data having the AL below -500nT. In contrast, the GEM storms have long periods with AL in the range of -1000nT. The prediction error measured with the average-relative variance (ARV) is of approximately unity. Reapplying the genetic algorithm the parameters shift such that the one long storm has an ARV=0.59. Physics modifications of the basic WINDMI model including the injection of sheet plasma into the ring current are being evaluated in terms of their impact on the ARV and comparisons with non-physics based signal processing prediction filters. Ensembles of initial conditions are run with 700MHz G3 CPU run times of order 17 sec per orbit per day of real data. The AMD AthlonXP 1700+ processor takes 5sec per orbit per day. The IBM SP-2 speed will be reported. With such speeds it is possible to run balls of initial conditions. Substrom Classification with the WINDMI Model, W. Horton, R.S. Weigel, D. Vassiliadis, and I. Doxas, Nonlinear Processes in Geophysics, 1-9, 2003. This work was supported by the National Science Foundation Grant ATM-0229863.

  16. Pitch angle diffusion in morningside aurorae 2. The formation of repetitive auroral pulsations

    Filling of the loss cone by pitch angle diffusion will quench the growth of VLF waves that interact with substorm-injected electrons in the morningside auroral region. This occurs for any wave mode whose growth rate is sensitive to the anisotropy of the electron distribution near the loss cone. A pair of coupled nonlinear differential equations is developed to describe the coupling between the growth of waves and the pitch angle diffusion of electrons. The equations differ from those previously used to model repetitive precipitation pulsations (Davidson, 1979) in that the wave growth in the earlier model was assumed to be sensitive mainly to the total electron flux. The earlier model therefore was limited by the strong diffusion lifetime. The pulsation periods in the earlier model were too long and strongly damped. The new model predicts cyclic or repetitive precipitation pulsations for a wide range of conditions, with periods of 3--30 s, and negligible damping. The model agrees well with an extensive body of observational data

  17. Conditions for substorm onset by the fast reconnection mechanism

    M. Ugai


    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.

  18. Magnetosphere energetics during substorm events IMP 8 and Geotail observations

    Belehaki, A


    Magnetospheric energetics during substorm events is studied in this paper. Three events were selected, a weak substorm, a large isolated one and finally a prolonged period of substorm activity with multiple intensifications. It is assumed that the energy, that entered the magnetosphere due to electromagnetic coupling with the solar wind, is described by the epsilon parameter, proposed by Perreault and Akasofu (1978). High resolution, magnetic field and plasma data from the MGF and LEP experiments on board Geotail were analyzed to determine the timing of plasmoid release, its dimensions, its convection velocity and finally the energy carried by each plasmoid. Plasmoids were defined as structures with rotating magnetic fields and enhanced total pressure. Tailward plasmoid bulk speed in the distant tail varied from 350 to 750 km/s. Their dimensions in the X/sub GSM/ direction was found to be from 4.5 to 28 R/sub E/, and their duration did not exceed 5 min. The average energy carried by each plasmoid in the dista...

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

    A. B. Collier


    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

  20. Auroral backscatter observed at HF from Ottawa

    Bistatic HF radar recordings of auroral scattering sources north of Ottawa are reported. Doppler frequency spreads over + or - 100 Hz were obtained at least 35 percent of the time. The peak of the Doppler frequency distribution was sometimes shifted from zero by as much as 50 Hz, and significant contributions often occurred at Doppler frequencies greater than 150 Hz. Signals received simultaneously on both arms of a two-arm direction-finding array were used to identify the specific elevations and bearings of the backscatter signals. A detailed study of a particular hour-long period is reported, and a large number of 'apparent' auroral backscatter sources are identified. The source regions, probably located in the F layer, were elongated mainly in the north-south direction and extended over at least 3 deg of latitude. North-south corridors were found between such sources in which echo returns were either absent or very weak. 14 references

  1. Auroral bright spot sequence near 14 MLT

    Optical observations of a dayside auroral brightening sequence, by means of all-sky TV cameras and meridian scanning photometers, have been combined with EISCAT ion drift observations within the same invariant latitude - MLT sector. The reported events, covering a 35 min interval around 14 MLT, are embedded within a longer period of similar auroral activity between 0830 (1200 MLT) and 1300 UT (1600 MLT). These observations are discussed in relation to recent models of boundary layer plasma dynamics and the associated magnetosphere-ionosphere coupling. The ionospheric events may correspond to large-scale wavelike motions of the low-latitude boundary layer. Based on this interpretation the observed spot size, speed and repetition period (∼ 10 min) give a wavelenght ∼ 900 km in the present case. The events can also be explained as ionospheric signatures of newly opened flux tubes associated with reconnection bursts at the magnetopause near 1400 MLT. 46 refs., 11 figs

  2. Monitoring auroral electrojets with satellite data

    Vennerstrøm, Susanne; Moretto, T.


    The strong horizontal ionospheric currents in the auroral oval constitute an important space weather parameter. Here we present a method to estimate the latitude location and intensity of these currents from measurements of variations in the magnetic field magnitude made by low Earth polar orbiting...... 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...... and complement existing ground-based indices. The CHAMP magnetometer in 350–450km altitude easily measures an electrojet which on the ground would produce an Auroral Electrojet (AE)-type signal as small as 20 nT. Thus, while the signal decreases roughly proportionally to the square of the distance to...

  3. A numerical simulation of auroral ionospheric electrodynamics

    Mallinckrodt, A. J.


    A computer simulation of auroral ionospheric electrodynamics in the altitude range 80 to 250 km has been developed. The routine will either simulate typical electron precipitation profiles or accept observed data. Using a model background ionosphere, ion production rates are calculated from which equilibrium electron densities and the Hall and Pedersen conductivities may be determined. With the specification of suitable boundary conditions, the entire three-dimensional current system and electric field may be calculated within the simulation region. The results of the application of the routine to a typical inverted-V precipitation profile are demonstrated. The routine is used to explore the observed anticorrelation between electric field magnitude and peak energy in the precipitating electron spectrum of an auroral arc.

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

    Moss, K.; P. Stauning


    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 cyc...

  5. Cluster in situ studies of the auroral acceleration region

    Li, Bin


    This thesis addresses a central topic in auroral physics, namely particle accelerationproducing intense aurora as well as energetic plasma outflow. Cluster satellitemeasurements of electric and magnetic fields, electrons and ions, collected across auroralfield lines, are used to study various aspects of the quasi-static auroral accelerationregion (AAR), its relation to the auroral density cavity, and the relative role of quasistaticand Alfvénic acceleration for producing aurora.The accelerati...

  6. Bursty reconnection modulating the substorm current wedge, a substorm case study re-analysed by ECLAT tools.

    Opgenoorth, Hermann; Palin, Laurianne; Ågren, Karin; Zivkovic, Tatjana; Facsko, Gabor; Sergeev, Victor; Kubyshkina, Marina; Nikolaev, Alexander; Milan, Steve; Imber, Suzanne; Kauristie, Kirsti; Palmroth, Minna; van de Kamp, Max; Nakamura, Rumi; Boakes, Peter


    Multi-instrumental data mining and interpretation can be tedious and complicated. In this context, the ECLAT (European Cluster Assimilation Technology) project was created to « provide a novel and unique data base and tools for space scientists, by providing an upgrade of the European Space Agency's Cluster Active Archive (CAA). » How can this new tool help the space plasma physics community? Here we demonstrate the power of coordinated global and meso-scale ground-based data to put satellite data into the proper context. We re-analyse a well-isolated substorm with a strong growth phase, which starts right overhead the Scandinavian network of instruments on 8 September 2002. This event was previously studied in detail by Sergeev et al (2005), based on a THEMIS-like configuration near-midnight using a unique radial constellation of LANL (~6.6Re), Geotail and Polar (~9Re), and Cluster (~16Re). In this new study we add detailed IMAGE spacecraft and ground-based network data. Magnetospheric models are specially adapted using solar wind conditions and in-situ observations. Simulation results are compared to the in-situ observations and discussed. We show how - both before and after substorm onset - bursty reconnection in the tail modulates the localised field aligned current flow associated with the substorm current wedge.

  7. Propagation of auroral hiss at high altitudes

    Santolík, Ondřej; Gurnett, D. A.


    Roč. 29, č. 10 (2002), s. 119-1-119-4, doi: 10.1029/2001GL013666. ISSN 0094-8276 R&D Projects: GA ČR GA205/01/1064 Grant ostatní: NASA(US) NAG5-7943 Institutional research plan: CEZ:AV0Z3042911; CEZ:MSM 113200004 Keywords : auroral hiss * electron beams * wave measurement Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 2.150, year: 2002

  8. The effect of magnetic substorms on near-ground atmospheric current

    Belova, E.; Kirkwood, S.; Tammet, H.


    Ionosphere-magnetosphere disturbances at high latitudes, e.g. magnetic substorms, are accompanied by energetic particle precipitation and strong variations of the ionospheric electric fields and currents. These might reasonably be expected to modify the local atmospheric electric circuit. We have analysed air-earth vertical currents (AECs) measured by a long wire antenna at Esrange, northern Sweden during 35 geomagnetic substorms. Using superposed epoch analysis we compare the air-earth current variations during the 3 h before and after the time of the magnetic X-component minimum with those for corresponding local times on 35 days without substorms. After elimination of the average daily variation we can conclude that the effect of substorms on AEC is small but distinguishable. It is speculated that the AEC increases observed during about 2 h prior to the geomagnetic X-component minimum, are due to enhancement of the ionospheric electric field. During the subsequent 2 h of the substorm recovery phase, the difference between substorm and quiet atmospheric currents decreases. The amplitude of this substorm variation of AEC is estimated to be less than 50% of the amplitude of the diurnal variation in AEC during the same time interval. The statistical significance of this result was confirmed using the Van der Waerden X-test. This method was further used to show that the average air-earth current and its fluctuations increase during late expansion and early recovery phases of substorms.

  9. Statistical study of the 'instantaneous' nightside auroral oval: The equatorward boundary of electron precipitation as observed by the Isis 1 and 2 satellites

    Electron spectrograms from 351 passes of the Isis 1 and 2 satellites were utilized to study statistically the effects of the interplanetary magnetic field (IMF), substorm activity, and the earth's dipole tilt angle on the latitude of the equatorward boundary of the nightside (2000--0400 magnetic local time) 'instantaneous' auroral oval. The boundary location (in invariant latitude) of the instantaneous oval at hourly local time intervals was identified in terms of the equatorward boundary of the diffuse >100-eV electron precipitation. The following characteristics were noted: (1) The north-south component (B/sub z/) of the IMF plays the dominant role in controlling the motion of this boundary. The invariant latitude of the boundary is shown to shift by approximately +- 40 depending on the direction of the IMF (northward and southward, respectively) relative to its position corresponding to B/sub z/=0. This indicates an inward motion of the associated boundary in the magnetotail by about 5 earth radii when the IMF changes its direction from northward to southward with large magnitude. There is a significant difference in the amount of the shift between the evening and morning sectors: i.e., for the same decrease in B/sub z/ value the boundary moves more equatorward in the morning sector than in the evening sector. When the obtained oval particle boundary was projected onto the equatorial plane of the magnetotail along magnetic field lines, good agreement was found between the projected boundary and the drift boundary (the Alfven layer) of low-energy electrons in the presence of the dawn-dusk electric field. (2) Substorm activity seems to have a separate role in determining the latitude of the equatorward boundary of the nightside auroral precipitation region

  10. Pi2 pulsations and substorm onsets: A review

    Olson, John V.


    Pi2 pulsations have been the subject of continuous study since they were recognized to be an integral part of the magnetospheric substorm. With the advent of arrays of ground instruments the nature of the Pi2 has begun to be understood. As adopted by the 13th General Assembly of the International Union of Geodesy and Geophysics in 1963, Pi2 is a designation that includes impulsive pulsations in the period range from 40 to 150 s. The Pi2 signal encompasses a class of pulsations that represents two fundamental processes. The first process is the sudden generation of field-aligned currents in association with the disruption of cross-tail currents in the plasma sheet and their subsequent effects on the ionosphere. The ionosphere appears to be something more than a passive load for this electrodynamic impulse. It responds, sending currents back into a magnetosphere whose topology is changing and, perhaps producing the feedback necessary to cause the explosive growth of the substorm current system. Oscillations of these currents are detected across the nightside of the Earth at onset as the midlatitude and high-latitude portions of Pi2. The second process is the impulse response of the inner magnetosphere to the compressional waves that are generated at substorm onset. Traveling inward, they stimulate field line resonances and surface waves at the plasmapause and excite global oscillations in the inner magnetosphere. The two processes produce wave modes that couple and cross-couple threading energy into the inner magnetosphere and ultimately to the ground. The purpose of this review is to construct a phenomenological overview of the Pi2.

  11. Turbulence-double-layer synergetic auroral electron acceleration

    In this letter we present a theoretical discussion on the problem of the auroral electron acceleration that supports the conjecture of wave-particle interaction (turbulence) assisting the auroral electron acceleration due to a dc magnetic field aligned electric field, created by a double layer, working as to enhance the electron flux

  12. "Old" tail lobes provide significant additional substorm power

    Mishin, V.; Mishin, V. V.; Karavaev, Y.


    In each polar cap (PC) we mark out "old PC" observed during quiet time before the event under consideration, and "new PC" that emerges during rounding the old one and expanding the PC total area. Old and new PCs correspond in the magnetosphere to the old and new tail lobes, respectively. The new lobe variable magnetic flux Ψ1 is usually assumed to be active, i.e. it provides transport of the electromagnetic energy flux (Poynting flux) ɛ' from solar wind into the magnetosphere. The old lobe magnetic flux Ψ2 is usually supposed to be passive, i.e. it remains constant during the disturbance and does not participate in the transporting process which would mean the old PC electric field absolute screening from the convection electric field created by the magnetopause reconnection. In fact, screening is observed, but it is far from absolute. We suggest a model of screening and determine its quantitative characteristics in the selected superstorm. The coefficient of a screening is the β = Ψ2/Ψ02, where Ψ02 = const is open magnetic flux through the old PC measured prior to the substorm, and Ψ2 is variable magnetic flux during the substorm. We consider three various regimes of disturbance. In each, the coefficient β decreased during the loading phase and increased at the unloading phase, but the rates and amplitudes of variations exhibited a strong dependence on the regime. We interpreted decrease in β as a result of involving the old PC magnetic flux Ψ2, which was considered to be constant earlier, to the ' transport process of the Poynting flux from the solar wind into the magnetosphere. A weakening of the transport process at the subsequent unloading phase creates increase in β. Estimates showed that coefficient β during each regime and the computed Poynting flux varied manifolds. In general, unlike the existing substorm conception, the new scenario describes an unknown earlier tail lobe activation process during a substorm growth phase that effectively

  13. Two theories of auroral electron acceleration

    Two theories of auroral electron acceleration are discussed. The first is the currently widely held view that the acceleration is an ordered process in a quasi-static electric field. It is suggested that, although there are many factors seeming to support this theory, the major qualifications and uncertainties that have been identified combine to cast serious doubt over its validity. The second is a relatively new interpretation in terms of stochastic acceleration in turbulent electric fields. This second theory, which appears to account readily for most known features of the electron distribution function, is considered to provide a more promising approach to this central question in magnetospheric plasma physics. (author)

  14. Correlation between ground-based observations of substorm signatures and magnetotail dynamics

    E. Borälv


    Full Text Available We present a substorm event study using the four Cluster spacecraft in combination with ground-based instruments, in order to perform simultaneous observations in the ionosphere and magnetotail. We show good correlation between substorm signatures on the ground and in the magnetotail, even though data from the northern-ground and southern-tail hemispheres are compared. During this event ground-based magnetometers show a substorm onset over Scandinavia in the pre-midnight sector. Within 1.5h the onset and three intensifications are apparent in the magnetograms. For all the substorm signatures seen on the ground, corresponding plasma sheet boundary motion is visible at Cluster, located at a downtail distance of 18.5 RE. As a result of the substorm onset and intensifications, Cluster moves in and out between the southern plasma sheet and lobe. Due to the lack of an apparent solar wind driver and the good correlation between substorm signatures on the ground, we conclude the substorm itself is the driver for these plasma sheet dynamics. We show that in the scales of Cluster inter-spacecraft distances (~0.5 RE the inferred plasma sheet motion is often directed in both Ygsm- and Zgsm-directions, and discuss this finding in the context of previous studies of tail flapping and plasma sheet thickness variations.

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

    P. Ritter


    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.

  16. The effect of magnetic substorms on near-ground atmospheric current

    E. Belova

    Full Text Available Ionosphere-magnetosphere disturbances at high latitudes, e.g. magnetic substorms, are accompanied by energetic particle precipitation and strong variations of the ionospheric electric fields and currents. These might reasonably be expected to modify the local atmospheric electric circuit. We have analysed air-earth vertical currents (AECs measured by a long wire antenna at Esrange, northern Sweden during 35 geomagnetic substorms. Using superposed epoch analysis we compare the air-earth current variations during the 3 h before and after the time of the magnetic X-component minimum with those for corresponding local times on 35 days without substorms. After elimination of the average daily variation we can conclude that the effect of substorms on AEC is small but distinguishable. It is speculated that the AEC increases observed during about 2 h prior to the geomagnetic X-component minimum, are due to enhancement of the ionospheric electric field. During the subsequent 2 h of the substorm recovery phase, the difference between "substorm" and "quiet" atmospheric currents decreases. The amplitude of this "substorm" variation of AEC is estimated to be less than 50% of the amplitude of the diurnal variation in AEC during the same time interval. The statistical significance of this result was confirmed using the Van der Waerden X-test. This method was further used to show that the average air-earth current and its fluctuations increase during late expansion and early recovery phases of substorms.

    Key words: Ionosphere (electric fields and currents · Magnetospheric physics (storms and substorms · Meteorology and atmospheric dynamics (atmospheric electricity

  17. Laboratory study of auroral cyclotron emission processes

    Ronald, Kevin


    Electrons encounter an increasing magnetic field and increase in pitch angle as they descend towards the auroral ionosphere, according to the conservation of the magnetic moment. This process results in a horseshoe shaped distribution function in electron velocity space which has been observed by satellites [1]. Research has shown this distribution to be unstable to a cyclotron maser instability [2] and the emitted Auroral Kilometric Radiation is observed to be polarised in the extraordinary mode. Experimental results are presented based on an electron beam of energy 75keV having a cyclotron frequency of 4.45GHz, compressed using magnet coils to mimic the naturally occurring phenomenon. The emitted radiation spectrum was observed to be close to the cyclotron frequency. Electron transport measurements confirmed that the horseshoe distribution function was obtained. Measurements of the antenna pattern radiated from the output window demonstrated the radiation to be polarised and propagating perpendicular to the static magnetic field. The radiation generation efficiency was estimated to be 2% in close agreement to the numerical predictions of the 2D PiC code KARAT. The efficiency was also comparable with estimates of the astrophysical phenomenon. [1] R. J. Strangeway et al, Geophys. Rev. Lett., 25, 1998, pp. 2065-2068 [2] I Vorgul et al, Physics of Plasmas, 12, 2005, pp. 1-8

  18. Carl Størmer Auroral Pioneer

    Egeland, Alv


    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.

  19. ISIS-II Scanning Auroral Photometer.

    Anger, C D; Fancott, T; McNally, J; Kerr, H S


    The ISIS-II dual wavelength scanning auroral photometer is designed to map the distribution of auroral emissions at 5577 A and 3914 A over the portion of the dark earth visible to the spacecraft. A combination of internal electronic scanning and the natural orbital and rotational motions of the spacecraft causes a dual wavelength photometer to be scanned systematically across the earth. The data will be reproduced directly in the form of separate pictures representing emissions at each wavelength, which will be used to study the large-scale distribution and morphology of auroras, to study the ratio of 3914-A and 5577-A emissions thought to depend upon the energies of exciting particles), and to compare with results from other instruments on board the spacecraft and on the ground. The Red Line Photometer experiment on the same spacecraft is described in an accompanying paper by Shepherd et al. [Appl. Opt. 12, 1767 (1973)]. The instrument can be thought of as the photometric equivalent of an all-sky color camera which will view the aurora from above instead of below and with a much wider vantage point unobstructed by cloud and haze. In one satellite pass, the instrument will be capable of surveying (in one hemisphere) the entire polar region in which auroras normally occur. PMID:20125605

  20. Cluster in the Auroral Acceleration Region

    Pickett, Jolene S.; Fazakerley, Andrew N.; Marklund, Gorun; Dandouras, Iannis; Christopher, Ivar W.; Kistler, Lynn; Lucek, Elizabeth; Masson, Arnaud; Taylor, Matthew G.; Mutel, Robert L.; Santolik, Ondrej; Bell, Timothy F.; Fung, Shing; Pottelette, Raymond; Hanasz, Jan; Schreiber, Roman; Hull, Arthur J.


    Due to a fortuitous evolution of the Cluster orbit, the Cluster spacecraft penetrated for the first time in its mission the heart of Earth's auroral acceleration region (AAR) in December 2009 and January 2010. During this time a special AAR campaign was carried out by the various Cluster instrument teams with special support from ESA and NASA facilities. We present some of the first multi-spacecraft observations of the waves, particles and fields made during that campaign. The Cluster spacecraft configuration during these AAR passages was such that it allowed us to explore the differences in the signatures of waves, particles, and fields on the various spacecraft in ways not possible with single spacecraft. For example, one spacecraft was more poleward than the other three (C2), one was at higher altitude (C1), and one of them (0) followed another (C4) through the AAR on approximately the same track but delayed by three minutes. Their separations were generally on the order of a few thousand km or less and occasionally two of them were lying along the same magnetic field line. We will show some of the first analyses of the data obtained during the AAR campaign, where upward and downward current regions, and the waves specifically associated with those regions, as well as the auroral cavities, were observed similarly and differently on the various spacecraft, helping us to explore the spatial, as well as the temporal, aspects of processes occurring in the AAR.

  1. An auroral westward flow channel (AWFC and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

    M. L. Parkinson


    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

  2. Preliminary results from Project Waterhole - an auroral modification experiment

    A sounding rocket carrying 100 kg of high explosives and plasma diagnostic instrumentation was launched from Churchill Research Ranch on 6 April 1980 over a premidnight auroral arc. The object of the experiment was to produce an ionospheric hole or plasma density depletion near 300 km altitude on field lines connected to an auroral arc. The plasma depletion is produced when the explosive by-products (mostly water) charge-exchange with the ambient O+ ions and then rapidly recombine. It was speculated that the presence of the 'hole' would interfere with the field-aligned current systems associated with the arc and would in turn perturb the auroral source mechanism. The release occurred about 10 km poleward of the auroral arc field lines. As expected, a large ionospheric hole was detected by the rocket-borne plasma sensors. Within a few seconds following the release, (a) the energetic electron precipitation observed in the hole dropped to background levels, (b) the luminosity of the auroral arc observed by a ground-based auroral scanning photometer decreased by a factor of two, and (c) the ionospheric E region density below the hole decayed at a rate consistent with a sudden reduction in particle precipitation. The simultaneous onset of these gross changes in electron precipitation coincident with the release strongly suggests a cause and effect relationship and demonstrates the intimate relationship that exists between the state of the ionospheric plasma and the auroral acceleration mechanism

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

    K. Moss


    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.

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

    Moss, K.; Stauning, P.


    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.

  5. Current Closure in the Auroral Ionosphere: Results from the Auroral Current and Electrodynamics Structure Rocket Mission

    Kaeppler, S. R.; Kletzing, C. A.; Bounds, S. R.; Gjerloev, J. W.; Anderson, B. J.; Korth, H.; LaBelle, J. W.; Dombrowski, M. P.; Lessard, M.; Pfaff, R. F.; Rowland D. E.; Jones, S.; Heinselman, C. J.


    The Auroral Current and Electrodynamics Structure (ACES) mission consisted of two sounding rockets launched nearly simultaneously from Poker Flat Research Range, AK on January 29, 2009 into a dynamic multiple-arc aurora. The ACES rocket mission was designed to observe electrodynamic and plasma parameters above and within the current closure region of the auroral ionosphere. Two well instrumented payloads were flown along very similar magnetic field footprints, at different altitudes, with small temporal separation between both payloads. The higher altitude payload (apogee 360 km), obtained in-situ measurements of electrodynamic and plasma parameters above the current closure region to determine the input signature. The low altitude payload (apogee 130 km), made similar observations within the current closure region. Results are presented comparing observations of the electric fields, magnetic components, and the differential electron energy flux at magnetic footpoints common to both payloads. In situ data is compared to the ground based all-sky imager data, which presents the evolution of the auroral event as the payloads traversed through magnetically similar regions. Current measurements derived from the magnetometers on the high altitude payload observed upward and downward field-aligned currents. The effect of collisions with the neutral atmosphere is investigated to determine if it is a significant mechanism to explain discrepancies in the low energy electron flux. The high altitude payload also observed time-dispersed arrivals in the electron flux and perturbations in the electric and magnetic field components, which are indicative of Alfven waves.

  6. Dynamics of the 1054 UT March 22, 1979, substorm event - CDAW 6. [Coordinated Data Analysis Workshop

    Mcpherron, R. L.; Manka, R. H.


    The Coordinated Data Analysis Workshop (CDAW 6) has the primary objective to trace the flow of energy from the solar wind through the magnetosphere to its ultimate dissipation in the ionosphere. An essential role in this energy transfer is played by magnetospheric substorms, however, details are not yet completely understood. The International Magnetospheric Study (IMS) has provided an ideal data base for the study conducted by CDAW 6. The present investigation is concerned with the 1054 UT March 22, 1979, substorm event, which had been selected for detailed examination in connection with the studies performed by the CDAW 6. The observations of this substorm are discussed, taking into account solar wind conditions, ground magnetic activity on March 22, 1979, observations at synchronous orbit, observations in the near geomagnetic tail, and the onset of the 1054 UT expansion phase. Substorm development and magnetospheric dynamics are discussed on the basis of a synthesis of the observations.

  7. Substorms observations over Apatity during geomagnetic storms in the period 2012 - 2016

    Guineva, Veneta; Werner, Rolf; Despirak, Irina; Kozelov, Boris


    In this work we studied substorms, generated during enhanced geomagnetic activity in the period 2012 - 2016. Observations of the Multiscale Aurora Imaging Network (MAIN) in Apatity have been used. Solar wind and interplanetary magnetic field parameters were judged by the 1-min sampled OMNI data base. Substorm onset and further development were verified by the 10-s sampled data of IMAGE magnetometers and by data of the all-sky camera at Apatity. Subject of the study were substorms occurred during geomagnetic storms. The so-called "St. Patrick's day 2015 event" (17-21 March 2015), the events on 17-18 March 2013 and 7-17 March 2012 (a chain of events generated four consecutive storms) which were among the events of strongest geomagnetic activity during the current solar cycle 24, were part of the storms under consideration. The behavior of the substorms developed during different phases of the geomagnetic storms was discussed.

  8. Physics of Substorm Growth Phase, Onset, and Dipolarization

    C.Z. Cheng


    A new scenario of substorm growth phase, onset, and depolarization during expansion phase and the corresponding physical processes are presented. During the growth phase, as a result of enhanced plasma convection, the plasma pressure and its gradient are continued to be enhanced over the quiet-time values in the plasma sheet. Toward the late growth phase, a strong cross-tail current sheet is formed in the near-Earth plasma sheet region, where a local magnetic well is formed, the plasma beta can reach a local maximum with value larger than 50 and the cross-tail current density can be enhanced to over 10nA/m{sup 2} as obtained from 3D quasi-static magnetospheric equilibrium solutions for the growth phase. The most unstable kinetic ballooning instabilities (KBI) are expected to be located in the tailward side of the strong cross-tail current sheet region. The field lines in the most unstable KBI region map to the transition region between the region-1 and region-2 currents in the ionosphere, which is consistent with the observed initial brightening location of the breakup arc in the intense proton precipitation region. The KBI explains the AMPTE/CCE observations that a low-frequency instability with a wave period of 50-75 seconds is excited about 2-3 minutes prior to substorm onset and grows exponentially to a large amplitude at the onset of current disruption (or current reduction). At the current disruption onset higher frequency instabilities are excited so that the plasma and electromagnetic field fluctuations form a strong turbulent state. Plasma transport takes place due to the strong turbulence to relax the ambient plasma pressure profile so that the plasma pressure and current density are reduced and the ambient magnetic field intensity increases by more than a factor of 2 in the high-beta(sub)eq region and the field line geometry recovers from tail-like to dipole-like dipolarization.

  9. Increases in plasma sheet temperature with solar wind driving during substorm growth phases

    Forsyth, C.; Watt, C E J; Rae, I. J.; Fazakerley, A. N.; Kalmoni, N.M.E.; Freeman, M. P.; P. D. Boakes; Nakamura, R; Dandouras, I.; L. M. Kistler; Jackman, C M; Coxon, J. C.; C. Carr


    During the substorm growth phase, magnetic reconnection extracts ~10^15 J from the solar wind through magnetic reconnection at the magnetopause, which is then stored in the magnetotail lobes. Plasma sheet pressure then increases to balance magnetic flux density increases in the lobes. We examine plasma sheet pressure, density and temperature during substorm growth phases using nine years of Cluster data (>316,000 data points). We show that plasma sheet pressure and temperature are higher duri...

  10. Localized activation of the distant tail neutral line just prior to substorm onsets

    Watanabe, Masakazu; Pinnock, Michael; Rodger, Alan S.; Sato, Natsuo; Yamagishi, Hisao; Yukimatu, A. Sessai; Greenwald, Raymond A.; Villain, Jean-Paul; Hairston, Marc R.


    We have found flow burst features in the nightside ionosphere that are thought to be the ionospheric signature of distant tail reconnection. These are observed to form just prior to substorm onsets. Simultaneous observations by the Goose Bay-Stokkseyri dual HF radars and DMSP satellites provide the data. Our conclusions are based on equatorward flow bursts on the nightside during two isolated substorms that followed a long period of magnetospheric inactivity associated with a northward interp...

  11. Seasonal-longitudinal variation of substorm occurrence frequency: Evidence for ionospheric control

    Wang, H.; Hermann Lühr


    Based on 2760 well-defined substorm onsets in the northern hemisphere and 1432 in the southern hemisphere observed by the FUV (Far Ultraviolet) Imager on board IMAGE (Imager for Magnetosphere-to-Aurora Global Exploration) spacecraft, a statistical study is performed for both hemispheres. The main emphasis is put on a possible dependence of the substorm occurrence frequency on season and longitude (S/L). It was found that around December solstice UT noon-time and around June solstice UT nightt...

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

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


    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....

  13. Ionospheric heating, upwelling, and depletions in auroral current systems

    Zettergren, M. D.; Semeter, J. L.


    This research investigates aspects of ionospheric dynamics relevant to magnetosphere-ionosphere coupling in auroral arc current systems. Auroral electric fields and particle precipitation deposit energy in the ionosphere, often resulting in enhanced ion or electron temperatures. This heating has a wide variety of consequences for the ionosphere. High ion temperatures alter chemical balance in the lower F-region, resulting in conversion to a molecular ion plasma, faster recombination, and plasma depletions. Pressure enhancements resulting from both ion and electron heating are capable of generating intense ion upflows. Ion upflow and depletion processes redistribute and structure the auroral plasma in ways that are likely of consequence to wave coupling of the magnetosphere and ionosphere. These implications are examined through the use of a fluid-kinetic model of the auroral ionosphere and new incoherent scatter radar data analysis techniques. Results indicate that enhanced recombination of molecular ions in auroral downward current regions may work in concert with well-known electrodynamic depletion processes, in the F-region ionosphere. Furthermore, ionospheric upflows in auroral upward and downward current regions may be quite different in terms of intensity and types of upflowing ions.

  14. Dayside Auroral Activity During Solar Maximum and Minimum Periods

    Rawie, M.; Fasel, G. J.; Flicker, J.; Angelo, A.; Bender, S.; Alyami, M.; Sibeck, D. G.; Sigernes, F.; Lorentzen, D. A.; Green, D.


    It is well documented that the dayside auroral oval shifts equatorward when the interplanetary magnetic field (IMF) Bz-component turns southward [Burch, 1973; Akasofu, 1977; Horwitz and Akasofu, 1977; Sandholt et al., 1986, 1988]. During these periods of oval expansion dayside transients are observed to move away from the poleward edge of the auroral oval and drift poleward. These poleward-moving auroral forms are believed to be ionospheric signatures of dayside merging. The dayside auroral oval usually begins to contract when the interplanetary magnetic field turns sharply northward, Bz>0. Eighteen years of meridian scanning photometer (MSP) data from the Kjell Henriksen Observatory in Longyearbyen, Norway are analyzed. During the boreal winter the Sun is several degrees below the horizon. This permits optical observations throughout the daytime period. The MSP Data is selected two hours before and after local noon in Longyearbeyn. Solar wind data (solar wind pressure and speed, along with the IMF Bx, By, Bz components) are collected for each interval and combined with the MSP observations. This data is then separated using solar maximum and minimum periods. Auroral activity (oval expansions and contractions along with the frequency and number of poleward-moving auroral forms) is documented for both solar maximum and minimum periods.

  15. Event study combining magnetospheric and ionospheric perspectives of the substorm current wedge modeling

    Sergeev, V. A.; Nikolaev, A. V.; Kubyshkina, M. V.; Tsyganenko, N. A.; Singer, H. J.; Rodriguez, J. V.; Angelopoulos, V.; Nakamura, R.; Milan, S. E.; Coxon, J. C.; Anderson, B. J.; Korth, H.


    Unprecedented spacecraft and instrumental coverage and the isolated nature and distinct step-like development of a substorm on 17 March 2010 has allowed validation of the two-loop substorm current wedge model (SCW2L). We find a close spatiotemporal relationship of the SCW with many other essential signatures of substorm activity in the magnetotail and demonstrate its azimuthally localized structure and stepwise expansion in the magnetotail. We confirm that ground SCW diagnostics makes it possible to reconstruct and organize the azimuthal spatiotemporal substorm development pattern with accuracy better than 1 h magnetic local time (MLT) in the case of medium-scale substorm. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE)-based study of global field-aligned current distribution indicates that (a) the SCW-related field-aligned current system consists of simultaneously activated R1- and R2-type currents, (b) their net currents have a R1-sense, and (c) locations of net current peaks are consistent with the SCW edge locations inferred from midlatitude variations. Thanks to good azimuthal coverage of four GOES and three Time History of Events and Macroscale Interactions during Substorms spacecraft, we evaluated the intensities of the SCW R1- and R2-like current loops (using the SCW2L model) obtained from combined magnetospheric and ground midlatitude magnetic observations and found the net currents consistent (within a factor of 2) with the AMPERE-based estimate. We also ran an adaptive magnetospheric model and show that SCW2L model outperforms it in predicting the magnetic configuration changes during substorm dipolarizations.

  16. Kinetic Ballooning Instability as a Substorm Onset Mechanism

    A new scenario of substorm onset and current disruption and the corresponding physical processes are presented based on the AMPTE/CCE spacecraft observation and a kinetic ballooning instability theory. During the growth phase of substorms the plasma beta is larger than unity (20 greater than or equal to beta greater than or equal to 1). Toward the end of the late growth phase the plasma beta increases from 20 to greater than or equal to 50 in approximately 3 minutes and a low-frequency instability with a wave period of 50 - 75 sec is excited and grows exponentially to a large amplitude at the current disruption onset. At the onset, higher-frequency instabilities are excited so that the plasma and electromagnetic field form a turbulent state. Plasma transport takes place to modify the ambient pressure profile so that the ambient magnetic field recovers from a tail-like geometry to a dipole-like geometry. A kinetic ballooning instability (KBI) theory is proposed to explain the low-frequency instability (frequency and growth rate) and its observed high beta threshold (beta subscript c is greater than or equal to 50). Based on the ideal-MHD theory beta subscript c, superscript MHD approximately equals 1 and the ballooning modes are predicted to be unstable during the growth phase, which is inconsistent with observation that no appreciable magnetic field fluctuation is observed. The enhancement beta subscript c over beta subscript c, superscript MHD is due to the kinetic effects of trapped electrons and finite ion-Larmor radii which provide a large stabilizing effect by producing a large parallel electric field and hence a parallel current that greatly enhances the stabilizing effect of field line tension. As a result, beta subscript c is greatly increased over beta subscript c, superscript MHD by a factor proportional to the ratio of the total electron density to the untrapped electron density (n subscript e divided by n subscript eu) which is greater than or equal to

  17. Theory for the asymmetry in the auroral ionization density profile for the generation of auroral infrasonic waves

    Traveling pressure waves with periods from 10 to 100 seconds are generated in the lower ionosphere by auroral electrojet current filaments as they move supersonically in an equatorward direction. The infrasonic waves produced by the auroral motions propagate to the ground as highly directional bow waves that can be detected by infrasonic microphones on the surface. There is an asymmetry in the reception of auroral infrasonic waves (AIW) with respect to whether the auroral arcs are moving equatorward to poleward. In the literature it is suggested that the asymmetry may be due to anisotropic propagation conditions along the acoustic ray path from the E-region, where AIW are produced, to the surface. Some intrinsic property of the AIW generation mechanism itself has also been suggested as a possible explanation. In this thesis anisotropic propagation is eliminated as the cause of the AIW reception asymmetry. Theoretical calculations, beginning with a model of an auroral precipitation region, are presented to show that there can be a significant difference in the transverse ionization density profiles between an auroral arc that is moving equatorward and an arc that is moving poleward, for a given equatorward-directed E-region ambient electric field. The calculation has been accomplished by solving the equations of motion and continuity for the cross-sectional ionization density profile associated with the transverse motion of a filamentary auroral electrojet. Thus, it is shown that there is an asymmetry in the ionization profiles associated with moving arcs, and in their coupling, that is related to the relative direction of motion of the arc with respect to the ambient electric field, and that it is this asymmetry that is probably the cause of the observed AIW reception asymmetry

  18. DMSP Auroral Charging at Solar Cycle 24 Maximum

    Chandler, M.; Parker, L. Neergaard; Minow, J. I.


    It has been well established that polar orbiting satellites can experience mild to severe auroral charging levels (on the order of a few hundred volts to few kilovolts negative frame potentials) during solar minimum conditions. These same studies have shown a strong reduction in charging during the rising and declining phases of the past few solar cycles with a nearly complete suppression of auroral charging at solar maximum. Recently, we have observed examples of high level charging during the recent approach to Solar Cycle 24 solar maximum conditions not unlike those reported by Frooninckx and Sojka. These observations demonstrate that spacecraft operations during solar maximum cannot be considered safe from auroral charging when solar activity is low. We present a survey of auroral charging events experienced by the Defense Meteorological Satellite Program (DMSP) F16 satellite during Solar Cycle 24 maximum conditions. We summarize the auroral energetic particle environment and the conditions necessary for charging to occur in this environment, we describe how the lower than normal solar activity levels for Solar Cycle 24 maximum conditions are conducive to charging in polar orbits, and we show examples of the more extreme charging events, sometimes exceeding 1 kV, during this time period.

  19. Energy transfer by magnetopause reconnection and the substorm parameter epsilon

    An expression for the magnetopause reconnection power based on the dawn-dusk component of the reconnection electric field, that reduces to the substorm parameter epsilon for the limit that involves equal geomagnetic (B sub(G)) and magnetosheath (B sub(M)) magnetic field amplitudes at the magnetopause, is contrasted with the expression based on the whole reconnection electric field vector obtained by Gonzalez. The correlation examples of this report show that this (more general) expression for the reconnection power seems to correlate with the empirical dissipation parameter U sub(T) from Akasofu, with slightly better correlation coefficients than those obtained from similar correlations between the parameter epsilon and U sub(T). Thus, these (better) correlations show up for the more familiar values of the ratio B sub(G) / B sub(M) > 1. Nevertheless, the (expected) relatively small difference that seems to exist between these correlation coefficients suggests that, for practical purposes, the parameter epsilon could be used as well (instead of the more general expression) in similar correlation studies due to its impler format. On the other hand, studies that refer mainly to the difference in the magnitudes of epsilon and of the more general expression are expected to give results with less negligible differences. (Author)

  20. Modeling Substorm Injections with a Simple Magnetotail model

    Kabin, Konstantin; Spanswick, Emma; Donovan, Eric; Kalugin, German


    Magnetotail dipolarizations, often associated with substorms, produce significant energetic particle enhancements in the night-time magnetosphere. We developed a simple yet self-consistent model for the electric and magnetic fields during dipolarizations, which is based on our earlier work (Kabin et al., JGR 2010). This model is very flexible and is particularly well suited for describing transition from the dipole-like to tail-like magnetic fields. We perform test particle simulations in the electric and magnetic fields specified by the model and find substantial energization of both electron and protons associated with the motion of this transition region. This energy gain is sufficient to explain many features of Dispersionless Injections. The energization of the particles is caused by betatron acceleration due to both the local increases in the magnetotail field strength during a dipolarization and to the particles drift closer to the Earth. In some cases the energy of an electron was found to increase by a factor of 25 or more. Our results are particularly well suited for comparison with riometer observations which often show clear signatures of Dispersionless Injections.

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

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


    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.

  2. Auroral Phenomenology and Magnetospheric Processes: Earth and Other Planets

    Schultz, Colin


    The dancing glow of the aurorae, the long tendrils of light that seem to reach up into space, has mesmerized scientists for centuries. More than a beautiful display, the aurorae tell us about the Earth—about its atmosphere, its magnetic field, and its relationship with the Sun. As technology developed, researchers looking beyond Earth's borders discovered an array of auroral processes on planets throughout the solar system. In the AGU monograph Auroral Phenomenology and Magnetospheric Processes: Earth and Other Planets, editors Andreas Keiling, Eric Donovan, Fran Bagenal, and Tomas Karlsson explore the many open questions that permeate the science of auroral physics and the relatively recent field of extraterrestrial aurorae. In this interview, Eos talks to Karlsson about extraterrestrial aurorae, Alfvén waves, and the sounds of the northern lights.

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

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


    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...

  4. Electric field measurements in the auroral E region

    Dipole electric field, positive ion and electron densities and temperatures, vehicle potential, and plasma sheath measurements have been made in the auroral E region by means of rockets flown from Fort Churchill, Canada. These results are described and compared over the altitude region 100 to 165 km. On a rocket flight launched on 10 December 1969 during very quiet conditions, adjacent to a stable, low intensity auroral arc, the plasma density and temperatures are found to be high and the electric fields large and steady. Electric field components of the order of -17 mv m-1 to +6 mv m-1 were measured along the Earth's magnetic field. The plasma results indicate that these fields may be contributing to enhanced electron temperatures. On a flight of 9 March 1970 during a large magnetic storm with widespread auroral activity, lower plasma densities and temperatures and much smaller and more erratic electric fields were observed with no significant component parallel to the magnetic field. (auth)

  5. Intermittency of storms and substorms: is it related to the critical behaviour?

    P. Dobias


    Full Text Available Intermittency is one of the possible means of quantifying dynamics of fractal processes. In this paper, the analysis of the intermittency of magnetospheric storms and substorms is presented. The analysis allows for a classification of the processes in terms of the power-law scaling of the magnitude of deviations of the index values from the values at quiet times (normal state, and the relative timings of occurrences of such deviations. These are expressed in terms of the co-dimension and the Fano factor. The relationship between the two is related to the nature of the processes behind the observed storm and substorm dynamics. The results suggest that there is a similarity between the two, and therefore it is possible that there are common dynamical processes behind the storms and substorms. In particular, it appears that both of them behave consistently with what would be expected for critical systems, which is consistent with the conclusions of several previous works.

  6. Estimates of magnetic flux, and energy balance in the plasma sheet during substorm expansion

    Hesse, Michael; Birn, Joachim; Pulkkinen, Tuija


    The energy and magnetic flux budgets of the magnetotail plasma sheet during substorm expansion are investigated. The possible mechanisms that change the energy content of the closed field line region which contains all the major dissipation mechanisms of relevance during substorms, are considered. The compression of the plasma sheet mechanism and the diffusion mechanism are considered and excluded. It is concluded that the magnetic reconnection mechanism can accomplish the required transport. Data-based empirical magnetic field models are used to investigate the magnetic flux transport required to account for the observed magnetic field dipolarizations in the inner magnetosphere. It is found that the magnetic flux permeating the current sheet is typically insufficient to supply the required magnetic flux. It is concluded that no major substorm-type magnetospheric reconfiguration is possible in the absence of magnetic reconnection.

  7. Auroral emission at Jupiter, through Juno's UVS eyes

    Grodent, Denis; Bonfond, Bertrand; Gladstone, G.; Gérard, Jean-Claude; Gustin, Jacques; Radioti, Aikaterini; Dumont, Maïté; Palmaerts, Benjamin; The Juno Science Team


    Juno’s orbit insertion around Jupiter will take place in little bit more than one year (July 2016). After a 107-day capture orbit (Oct. 2016), it will perform a series of 33 eleven-day science polar orbits offering unprecedented views of the auroral regions of Jupiter. The science payload of Juno includes an UltraViolet Spectrograph (UVS) that will characterize the UV auroral emissions of Jupiter over all science orbits. It will obtain high-resolution images and spectra that will provide cont...

  8. Auroral electron acceleration by lower-hybrid waves

    Because the particles and electric fields association with inverted-V electron streams do not have the characteristics expected for acceleration by a quasistatic potential difference, the possiblity that the electrons are stochastically accelerated by waves is investigated. It is demonstrated that the lower hybrid waves seen on auroral field lines have the righ properties to account for the electron acceleration. It is further shown that the lower hybrid wave power measured on auroral field lines can be generated by the streaming ions observed at the boundary of the plasma sheet, and that this wave power is sufficient to account for the electron power observed close to the atmosphere. (author)

  9. V and V Efforts of Auroral Precipitation Models: Preliminary Results

    Zheng, Yihua; Kuznetsova, Masha; Rastaetter, Lutz; Hesse, Michael


    Auroral precipitation models have been valuable both in terms of space weather applications and space science research. Yet very limited testing has been performed regarding model performance. A variety of auroral models are available, including empirical models that are parameterized by geomagnetic indices or upstream solar wind conditions, now casting models that are based on satellite observations, or those derived from physics-based, coupled global models. In this presentation, we will show our preliminary results regarding V&V efforts of some of the models.

  10. Analysis of auroral infrared emissions observed during the ELIAS experiment

    G. E. Caledonia

    Full Text Available The ELIAS (Earth Limb Infrared Atmospheric Structure experiment was flown from the Poker Flat Research Range, Alaska in 1983 and successfully monitored visible and infrared emissions from an IBC III+ aurora. Measurements were performed in both staring and scanning modes over several hundred seconds. The data for short- and mid-wave infrared regions have been analyzed in terms of auroral excitation of the NO and NO+ vibrational bands. Auroral excitation efficiencies and kinetic implications are presented.