Peculiarities of the outer radiation belt dynamics during the strong magnetic storm of May 15, 2005

The dynamics of energetic electrons (E _e =0.17–8 MeV) and protons (E _p =1 MeV) of the outer radiation belt during the magnetic storm of May 15, 2005, at high (GOES-10 and LANL-84 geosynchronous satellites) and low (Meteor-3M polar satellite) altitudes is analyzed. The data have been compared to the density, plasma velocity, solar wind, and magnetic field measurements on the ACE satellite and geomagnetic disturbances. During the magnetic storm main phase, the nighttime boundary of the region of trapped radiation and the center of westward electrojet shifted to L ～ 3. Enhancements of only low-energy electrons were observed on May 15, 2005. The belt of relativistic electrons with a maximum at L ～ 4 was formed during the substorm, the amplitude of which reached its maximum at ～0630 UT on May 16. The results are in good agreement with the regularity relating the position of a maximum of the new relativistic electron belt, boundaries of the trapped radiation region, and extreme low-latitude position of westward electrojet center to the Dst variation amplitude.     

Diagnostics of the magnetosphere based on the outer belt relativistic electrons and penetration of solar protons: A review

The present-day state of the studies of the outer radiation belt relativistic electrons and the boundary of the solar proton penetration into the magnetosphere during magnetic storms is briefly reviewed. The main attention is paid to the results from studying the interrelation between these structural formations and other magnetospheric plasma structures. It has been indicated that the relationship between the position of the maximum of belt of relativistic electrons injected during magnetic storms (L _max) and the magnetic storm amplitude (|Dst|_max = 2.75 × 10⁴/L _max⁴) can be used to predict the extreme latitudinal position of such magnetospheric plasma formations as a trapped radiation region boundary, the nighttime equatorial boundary of the auroral oval, and westward electrojet center during a storm. Using the examples of still rare studies of the solar proton boundary dynamics in the magnetosphere based on the simultaneous measurements on several polar satellites, it has been demonstrated that a change in the geomagnetic field topology during magnetic storms can be diagnosed.     

Variations in the near-surface atmospheric electric field at high latitudes and ionospheric potential during geomagnetic perturbations

We have analyzed variations in the near-surface atmospheric electric field (Ez) normalized to their daily averages that were simultaneously observed in different high-latitude regions at moderate geomagnetic activity (Kp ∼ 3). The Ez data were measured under fair weather conditions at the Vostok Antarctic research station (Φ′ = −83.5°) in the southern polar cap and at the Hornsund Arctic observatory (Φ′ = 74.0°) on Svalbard close to the polar boundary of the auroral oval in the Northern Hemisphere. It is established that variations in the atmospheric electric field in the polar cap region at the Vostok station are controlled (the correlation coefficient R ∼ 0.7–0.9) by variations in the overhead ionospheric potential. The situation at the Hornsund observatory is more complicated. During intervals when Hornsund occurred below the westward electrojet, the correlation was typically positive with R ∼ 0.60–0.85; however, while this observatory was in the region of the eastern electrojet, the correlation could be negative with R ∼ 0.7–0.8. Normally, during such periods, the westward electrojet was detected polarwards of Hornsund while, according to the SuperDARN radar data, the observatory was located below the negative vortex of the polar ionospheric convection.     

Assessment of the possibility of using E. A. Ponomarev’s magnetospheric substorm model to analyze geomagnetic disturbances during the magnetic storms of December 14 and 15, 2006

Spatial distributions of pressure and fluxes of precipitating magnetospheric plasma particles were constructed for the strong magnetic storm of December 14 and 15, 2006. The calculations were performed using a model developed by E.A. Ponomarev. Geotail and ACE satellite data were used to specify realistic initial and boundary conditions. The model results were compared with the spatial distribution of the field of geomagnetic disturbances recorded by ground-based magnetic observatories during the storm. The results show that the model (in its current form) provides good agreement between latitudinal displacements of electron precipitations and auroral electrojets but fails to reflect their longitudinal structure. The model fails to yield the strong westward electrojet observed by all auroral zone observatories during the main phase of the magnetic storm.     

About the relationship between auroral electrojets and ring currents

The relationship between the storm-time ring current and the auroral electrojets is investigated using IMAGE magnetometer data, D_St 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 D_St. 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.     

Global geomagnetic and auroral response to variations in the solar wind dynamic pressure on April 1, 1997

The geomagnetic and auroral response to the variations in the solar wind dynamic pressure (Pd) are investigated in the periods of positive values of the IMF B _z component. It is shown that the growth of Pd results in the intensification of luminosity along the auroral oval and in the poleward expansion of the poleward boundary of luminosity (PBL) in the nightside part of the oval by ～7° in latitude at a velocity of ～0.5 km/s and is accompanied by an enhancement of the DP2-type current system. A decrease in Pd, accompanied by an abrupt reversal of the IMF B _y polarity from positive to negative, results in an enhancement of the westward electrojet and in a poleward shift of PBL and electrojet center. The conclusion has been made that the available three types of auroral response to Pd variations differ in the azimuthal velocity of the luminosity region or particle precipitation along the auroral oval: V ₁ ～ 30–40 km/s, V ₂ ～ 10, and V ₃ ～ 1 km/s.     

对流电场、场向电流和极光区电集流变化的地磁响应

对流电场、场向电流和极光区电集流是磁层一电离层耦合的主要物理过程．它们的演化发展时间分别为几分钟至半小时的量级．本文用１００°Ｅ和３００°Ｅ的两个地磁经度链附近各１１个台站的１ｍｉｎ均值地磁Ｈ和Ｚ分量资料,分析了１９９４年４月１６-１７日磁暴期间磁层耦合过程对极光区和中低纬区电离层扰动的地磁特征．强磁暴开始时,台站所处的地方时位置不同,则观测到的电离层和地磁响应也完全不同．这是磁层对流和一、二区场向电流共同作用的结果．一般说,扰时极光区的西向电集流变化更为强烈．随着耦合的发展,极光区范围会向南北扩展,电集流中心带则向低纬侧移动．在中低纬区,二区场向电流的建立能屏蔽一区场向电流所产生的扰动,并引起反向的电流及地磁变化．由此,中低纬区夜间有可能出现短时间的东向电场,又可通过ＥＸＢ的垂直向上漂移作用抬升Ｆ层等离子体,并发生同一经度链附近的多站电离层ｈ＇Ｆ同时突增现象．另一方面,磁赤道附近的台站则更多地受内磁层赤道环电流和电离层赤道电集流的影响．     

Auroral electrojet dynamics during magnetic storms, connection with plasma precipitation and large-scale structure of the magnetospheric magnetic field

Effect of the equatorward shift of the eastward and westward electrojets during magnetic storms main phase is analyzed based on the meridional chains of magnetic observatories EISCAT and IMAGE and several Russian observatories (geomagnetic longitude ≈110°, corrected geomagnetic latitudes 74°>φ>51°.) Magnetic storms of various Dst index intensity where the main phase falls on 1000 UT - 2400 UT interval were selected so that one of the observatory chains was located in the afternoon - near midnight sector of MLT. The eastward electrojet center shifts equatorward with Dst intensity increase: when Dst ≈ −50 nT the electrojet center is located at φ ≈ 62°, when Dst ≈ −300 nT it is placed at φ ≈ 54°. The westward electrojet center during magnetic storms main phase for intervals between substorms shifts equatorward with Dst increase: at φ ≈ 62° when Dst ≈ −100 nT and at φ ≈ 55° when Dst ≈ −300 nT. During substorms within the magnetic storms intervals the westward electrojet widens poleward covering latitudes φ ≈ 64°–65°. DMSP (F08, F10 and F11) satellite observations of auroral energy plasma precipitations at upper atmosphere altitudes were used to determine precipitation region structure and location of boundaries of various plasma domains during magnetic storms on May 10–11, 1992, February 5–7 and February 21–22, 1994. Interrelationships between center location, poleward and equatorward boundaries of electrojets and characteristic plasma regions are discussed. The electrojet center, poleward and equatorward boundaries along the magnetic observatories meridional chain were mapped to the magnetosphere using the geomagnetic field paraboloid model. The location of auroral energy oxygen ion regions in the night and evening magnetosphere is determined. Considerations are presented on the mechanism causing the appearance in the inner magnetosphere during active intervals of magnetic storms of ions with energy of tens KeV. In the framework of the magnetospheric magnetic field paraboloid model the influence of the ring current and magnetospheric tail plasma sheet currents on large-scale magnetosphere structure is considered.     

Unusual spatial-temporal dynamics of geomagnetic disturbances during the main phase of the extremely strong magnetic storm of November 7–8, 2004

The spatial dynamics of geomagnetic variations and pulsations, auroras, and riometer absorption during the development of the main phase of the extremely strong magnetic storm of November 7–8, 2004, has been studied. It has been indicated that intense disturbances were observed in the early morning sector of auroral latitudes rather than in the nighttime sector, as usually takes place during magnetic storms. The unusual spatial dynamics was revealed at the beginning of the storm main phase. A rapid poleward expansion of disturbances from geomagnetic latitudes of 65°–66° to 74°–75° and the development of the so-called polar cap substorm with a negative bay amplitude of up to 2500 nT, accompanied by precipitation of energetic electrons (riometer absorption) and generation of Pi2–Pi3 pulsations, were observed when IMF B _z was about ?45 nT. The geomagnetic activity maximum subsequently sharply shifted equatorward to 60°–61°. The spatial dynamics of the westward electrojet, Pi2–Pi3 geomagnetic pulsations, and riometer absorption was similar, which can indicate that the source of these phenomena is common.     

Development of geomagnetic storm in VLF noise

The complex geophysical pattern of the development of geomagnetic storm in VLF emissions has been studied based on the satellite data. It has been established that the variations in the LF noise emission intensity (0.1–20.0 kHz) and the energetic electron (E ≥ 40 keV) flux density reflect the processes of magnetospheric plasma reconstruction during geomagnetic disturbances. It has been indicated that a distinct structure of the inner and outer radiation belts is observed under quiet conditions, and the VLF emission maximum was registered at L = 4–5. The inner boundary of the outer radiation belt shifted to lower latitudes, the intensity of the noise VLF emissions increased, and the intensity maximum was displaced to L = 2.5–3.5 during the geomagnetic storm, when the energetic electron flux density increased. The VLF noise spectrum widened toward higher frequencies. The VLF noise level continued increasing, the noise maximum shifted to L = 4–5, and the fluxes of precipitating electrons abruptly increased during the storm recovery phase, when the density of the flux of quasitrapped electrons remained increased for a long time.     

亚暴期间极光电集流带的变化

极光活动加剧和极光电集流增强是磁层-电离层能量耦合的两种重要表现形式,它们同为磁层带电粒子向电离层沉降的结果,但是变化规律却非常不同.本文用地基磁场资料,反演极区等效电流体系,研究地磁平静期和扰动期极光电集流带的运动特点.研究表明,Harang间断把极光电集流带分为两段：下午—黄昏段的东向电集流带较弱,而晨侧和子夜—凌晨段的西向电集流带较强.在亚暴膨胀相,随着AE指数增大,整个极光卵向赤道扩展,而极光电集流带却表现出分段差异的特点：下午—黄昏东向电集流带向低纬移动,晨侧西向电集流带也向赤道移动,而子夜—凌晨西向电集流带则向极移动.电动力学分析表明,在不同地方时段,控制电流的主要因素不同,因而,电流及其磁扰有不同的特点：下午—黄昏东向电集流和晨侧西向电集流组成了DP2电流体系,主要受控于磁层对流电场,反映了“驱动过程”的行为;而子夜—凌晨西向电集流是DP1电流体系的基本部分,主要受控于电导率,反映了“卸载过程”的特点.     

The response of ionospheric convection in the polar cap to substorm activity

We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°-78°. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71° by the time of the expansion phase onset. A westward electrojet, centred at 65.4°, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1° at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the “distant” neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary.     

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

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 B_z variations than the symmetric ring current. ASY increases (decreases) faster during the main phase (the recovery phase) than DR. The magnetic field decay at low latitudes in the recovery phase occurs faster in the afternoon sector than at dusk.     

Quantitative analysis of the relationship between polar ionospheric currents and auroral electrojet indices

Magnetic storms and substorms are principalprocesses of energy transition from the solar wind intothe magnetosphere-ionosphere system and dissipationin the system. They are also important events whichthe space physics study and space weather predictionhave been focused on. Magnetic storms are describedby means of the magnetic index Dst, which is calcu-lated using the magnetic disturbances of horizontalcomponent recorded at 5 low-latitudinal stations, rep-resenting approximately the symmetric r…     

High-latitude geomagnetic disturbances during the initial phase of a recurrent magnetic storm (from February 27 to March 2, 2008)

A complex of geophysical phenomena (geomagnetic pulsations in different frequency ranges, VLF emissions, riometer absorption, and auroras) during the initial phase of a small recurrent magnetic storm that occurred on February 27–March 2, 2008, at a solar activity minimum has been analyzed. The difference between this storm and other typical magnetic storms consisted in that its initial phase developed under a prolonged period of negative IMF B _z values, and the most intense wave-like disturbances during the storm initial phase were observed in the dusk and nighttime magnetospheric sectors rather than in the daytime sector as is observed in the majority of cases. The passage of a dense transient (with N _p reaching 30 cm⁻³) in the solar wind under the southward IMF in the sheath region of the high-speed solar wind stream responsible for the discussed storm caused a great (the AE index is ∼1250 nT) magnetospheric substorm. The appearance of VLF chorus, accompanied by riometer absorption bursts and Pc5 pulsations, in a very long longitudinal interval of auroral latitudes (L ∼ 5) from premidnight to dawn MLT hours has been detected. It has been concluded that a sharp increase in the solar wind dynamic pressure under prolonged negative values of IMF B _z resulted in the global (in longitude) development of electron cyclotron instability in the Earth’s magnetosphere.     

用我国地磁资料对磁层大尺度扰动之赤道电急流效应的初步分析

本文利用我国琼中、广州、泉州三站1982-1983年地磁Z分量资料,对磁暴主相发展及恢复相初期的赤道电急流变化进行了研究。形态分析、周期叠加和相关分析均表明,不论在何地方时,对应环电流的发展有△Z的负扰（附加东向电急流）;而D_st开始回升则有△Z的正扰（附加西向电急流）。该变化之大小可能受地方时的调制。方差分析、x²-分析等统计检验也认证了上述变化。文中还对△Z正、负扰与极区电急流及极尖区位置的高、低纬向移动进行了讨论。本文结果表明,分析扰日赤道电急流变化应区分磁暴的不同阶段,即区分电动耦合和动力耦合效应。今后应采用大范围台站网资料,进一步得出有关电流系的图象。     

Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm

On August 21st 1998, a sharp southward turning of the IMF, following on from a 20 h period of northward directed magnetic field, resulted in an isolated substorm over northern Scandinavia and Svalbard. A combination of high time resolution and large spatial scale measurements from an array of coherent scatter and incoherent scatter ionospheric radars, ground magnetometers and the Polar UVI imager has allowed the electrodynamics of the impulsive substorm electrojet region during its first few minutes of evolution at the expansion phase onset to be studied in great detail. At the expansion phase onset the substorm onset region is characterised by a strong enhancement of the electron temperature and UV aurora. This poleward expanding auroral structure moves initially at 0.9 km s^-1 poleward, finally reaching a latitude of 72.5°. The optical signature expands rapidly westwards at ~6 km s^-1, whilst the eastward edge also expands eastward at ~0.6 km s^-1. Typical flows of 600 m s^-1 and conductances of 2 S were measured before the auroral activation, which rapidly changed to ~100 m s^-1 and 10–20 S respectively at activation. The initial flow response to the substorm expansion phase onset is a flow suppression, observed up to some 300 km poleward of the initial region of auroral luminosity, imposed over a time scale of less than 10 s. The high conductivity region of the electrojet acts as an obstacle to the flow, resulting in a region of low-electric field, but also low conductivity poleward of the high-conductivity region. Rapid flows are observed at the edge of the high-conductivity region, and subsequently the high flow region develops, flowing around the expanding auroral feature in a direction determined by the flow pattern prevailing before the substorm intensification. The enhanced electron temperatures associated with the substorm-disturbed region extended some 2° further poleward than the UV auroral signature associated with it.     

Dayside isotropic precipitation of energetic protons

Recently it has been shown that isotropic precipitation of energetic protons on the nightside is caused by a non-adiabatic effect, namely pitch-angle scattering of protons in curved magnetic field lines of the tail current sheet. Here we address the origin of isotropic proton precipitation on the dayside. Computations of proton scattering regions in the magnetopheric models T87, T89 and T95 reveal two regions which contribute to the isotropic precipitation. The first is the region of weak magnetic field in the outer cusp which provides the 1–2° wide isotropic precipitation on closed field lines in a 2–3 hour wide MLT sector centered on noon. A second zone is formed by the scattering on the closed field lines which cross the nightside equatorial region near the magnetopause which provides isotropic precipitation starting 1.5–2 h MLT from noon and which joins smoothly the precipitation coming from the tail current sheet. We also analyzed the isotropic proton precipitation using observations of NOAA low altitude polar spacecraft. We find that isotropic precipitation of >30 to > 80 keV protons continues around noon forming the continuous oval-shaped region of isotropic precipitation. Part of this region lies on open field lines in the region of cusp-like or mantle precipitation, its equatorward part is observed on closed field lines. Near noon it extends 1–2° below the sharp boundary of solar electron fluxes (proxy of the open/closed field line boundary) and equatorward of the cusp-like auroral precipitation. The observed energy dispersion of its equatorward boundary (isotropic boundary) agrees with model predictions of expected particle scattering in the regions of weak and highly curved magnetic field. We also found some disagreement with model computations. We did not observe the predicted split of the isotropic precipitation region into separate nightside and dayside isotropic zones. Also, the oval-like shape of the isotropic boundary has a symmetry line in 10–12 MLT sector, which with increasing activity rotates toward dawn while the latitude of isotropic boundary is decreasing. Our conclusion is that for both dayside and nightside the isotropic boundary location is basically controlled by the magnetospheric magnetic field, and therefore the isotropic boundaries can be used as a tool to probe the magnetospheric configuration in different external conditions and at different activity levels.     

Local particle traps in the high latitude magnetosphere and the acceleration of relativistic electrons

Variations of electron fluxes with energies 300–600 keV in the region of quasitrapping are analyzed using data of the low orbiting Coronas-F satellite. Enhancements in the electron fluxes with energies above 300 keV are observed at the polar boundary of the outer radiation belt. Meteor-3M satellite data, OVATION and AP models of the position of the auroral oval are used to determine the position of analyzed increases in the energetic electrons with respect to the position of the auroral oval. There is a significant number of events when these increases were observed at a few consequent orbits crossing the outer radiation belt boundary. Studied increases in relativistic electron fluxes are localized at the latitudes of the auroral oval. Different mechanisms of formation of observed enhancements are discussed. The possibility of the appearance of increases due to formation of local particle traps is analyzed using Tsyganenko geomagnetic field models. The role of the formation of local particle traps at the boundary of the outer radiation belt and its possible influence to the formation of the outer radiation belt is discussed.     

PFISR observations of strong azimuthal flow bursts in the ionosphere and their relation to nightside aurora

Flow bursts within the ionosphere are the ionospheric signatures of flow bursts in the plasma sheet and have been associated with poleward boundary intensifications (PBIs). Some PBIs extend equatorward from the polar cap boundary, where they can be roughly divided into north–south-aligned and east–west-aligned structures. In this paper, we present two flow burst events observed by the new Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) in the pre-midnight auroral zone on 28 April 2007, one towards the west and the other towards the east. In both cases, enhanced flows lasted for about 8–10 min with peak velocities exceeding 1500 m/s. The concurrently measured electron density showed that the flow bursts occurred in low conductivity regions. However, near the poleward (equatorward) edge of the westward (eastward) flow burst, strong electron density enhancements were observed in the E region, indicating the presence of discrete auroral arcs. Auroral images from the Polar spacecraft were available at the time of the eastward flow burst and they indicate that this burst was associated with an east–west-aligned auroral structure that connected at later MLT to a north–south structure. In addition, simultaneous precipitating particle energy spectrum measured by the the Defense Meteorological Satellites Program (DMSP) F13 satellite reveals that this auroral structure resulted from mono-energetic electron precipitation associated with a significant field-aligned potential drop. These observations show direct evidence of the relationship between flow bursts, field-aligned currents and auroral intensifications, and suggest that eastward/westward flow bursts are associated with east–west-oriented PBI structures that have extended well within the plasma sheet. This is in contrast to the equatorward-directed flow that has been previously inferred for PBIs near the polar cap boundary and for north–south auroral structures. This paper illustrates the use of the PFISR radar for studying the magnetosphere–ionosphere coupling of flow bursts.