Prediction of maximal daily average values of relativistic electron fluxes in geostationary orbit during the magnetic storm recovery phase

The relation of the maximal daily average values of the relativistic electron fluxes with an energy higher than 2 MeV, obtained from the measurements on GOES geostationary satellites, during the recovery phase of magnetic storms to the solar wind parameters and magnetospheric activity indices has been considered. The parameters of Pc5 and Pi1 geomagnetic pulsations and the relativistic electron fluxes during the prestorm period and the main phase of magnetic storms have been used together with the traditional indices of geomagnetic activity (A _E, K _p, D _st). A simple model for predicting relativistic electron fluxes has been proposed for the first three days of the magnetic storm recovery phase. The predicted fluxes of the outer radiation belt relativistic electrons well correlate with the observed values (R ∼ 0.8–0.9).     

Relativistic electron losses related to EMIC waves during CIR and CME storms

The losses of radiation belt electrons to the atmosphere due to wave–particle interactions with electromagnetic ion-cyclotron (EMIC) waves during corotating interaction region (CIR) storms compared to coronal mass ejections (CME) storms is investigated. Geomagnetic storms with extended ‘recovery’ phases due to large-amplitude Alfvén waves in the solar wind are associated with relativistic electron flux enhancements in the outer radiation belt. The corotating solar wind streams following a CIR in the solar wind contain large-amplitude Alfvén waves, but also some CME storms with high-speed solar wind can have large-amplitude Alfvén waves and extended ‘recovery’ phases. During both CIR and CME storms the ring current protons are enhanced. In the anisotropic proton zone the protons are unstable for EMIC wave growth. Atmospheric losses of relativistic electrons due to weak to moderate pitch angle scattering by EMIC waves is observed inside the whole anisotropic proton zone. During storms with extended ‘recovery’ phases we observe higher atmospheric loss of relativistic electrons than in storms with fast recovery phases. As the EMIC waves exist in storms with both extended and short recovery phases, the increased loss of relativistic electrons reflects the enhanced source of relativistic electrons in the radiation belt during extended recovery phase storms. The region with the most unstable protons and intense EMIC wave generation, seen as a narrow spike in the proton precipitation, is spatially coincident with the largest loss of relativistic electrons. This region can be observed at all MLTs and is closely connected with the spatial shape of the plasmapause as revealed by simultaneous observations by the IMAGE and the NOAA spacecraft. The observations in and near the atmospheric loss cone show that the CIR and CME storms with extended ‘recovery’ phases produce high atmospheric losses of relativistic electrons, as these storms accelerate electrons to relativistic energies. The CME storm with short recovery phase gives low losses of relativistic electrons due to a reduced level of relativistic electrons in the radiation belt.     

The relation between geomagnetic pulsations and an increase in the fluxes of geosynchronous relativistic electrons during geomagnetic storms

The dynamics of the Pc5 and Pi1 pulsation characteristics and relativistic electron fluxes at geostationary orbit were comparatively analyzed for three nine-day intervals, including quiet periods and periods of geomagnetic storms. It was shown that relativistic electron fluxes increase considerably when the power of global Pc5 pulsations and the index of midlatitude irregular Pi1 pulsations increase simultaneously. The correlation between the characteristics of Pi1 and Pc5 geomagnetic pulsations and the level of the relativistic electron flux at geostationary orbit during the magnetic storm recovery phase were studied. It was shown that the correlation coefficient of the relativistic electron maximal fluxes during the magnetic storm recovery phase with the parameter of midlatitude Pi1 pulsations is slightly higher than such a correlation coefficient with the solar wind velocity.     

The recovery phase of the superstrong magnetic storm of July 15–17, 2000: Substorms and ULF pulsations

The geomagnetic observations, performed at the global network of ground-based observatories during the recovery phase of the superstrong magnetic storm of July 15–17, 2000 (Bastille Day Event, Dst = ?301 nT), have been analyzed. It has been indicated that magnetic activity did not cease at the beginning of the storm recovery phase but abruptly shifted to polar latitudes. Polar cap substorms were accompanied by the development of intense geomagnetic pulsations in the morning sector of auroral latitudes. In this case oscillations at frequencies of 1–2 and 3–4 mHz were observed at geomagnetic latitudes higher and lower than ～62°, respectively. It has been detected that the spectra of variations in the solar wind dynamic pressure and the amplitude spectra of geomagnetic pulsations on the Earth’s surface were similar. Wave activity unexpectedly appeared in the evening sector of auroral latitudes after the development of near-midnight polar substorms. It has been established that the generation of Pc5 pulsations (in this case at frequencies of 3–4 mHz) was spatially asymmetric about noon during the late stage of the recovery phase of the discussed storm as took place during the recovery phase of the superstrong storms of October and November 2003. Intense oscillations were generated in the morning sector at the auroral latitudes and in the postnoon sector at the subauroral and middle latitudes. The cause of such an asymmetry, typical of the recovery phase of superstrong magnetic storms, remains unknown.     

磁层相对论电子通量变化与磁暴/亚暴的关系

本文分析了1 AU处的行星际磁场、太阳风速度、Kp指数、Dst和AE的变化关系，以及它们和地球同步轨道附近相对论电子通量的变化关系.分析说明，当行星际磁场Bz分量出现南向扰动和太阳风速度增大超过500 km/s时，地球磁层中常常发生磁暴/亚暴活动.在磁暴主相期间，相对论电子(能量E≥1 MeV)通量下降；而在磁暴恢复相期间，相对论电子通量恢复上升.但是，只有在伴随有高强度（AE≥500 nT）的持续性亚暴活动的磁暴恢复相期间，相对论电子的通量才能增长到超过暴前通量值，且能量低于300 keV的亚暴电子的通量越高，相对论电子的通量越高，反之则越低.亚暴注入电子数的多少很大程度上决定了磁暴恢复相期间相对论电子数的多少，这说明亚暴活动注入能量低于300 keV的亚暴电子是磁层相对论电子的一个重要来源.     

行星际扰动和地磁活动对GEO相对论电子影响

利用1988—2010年小时平均的GOES卫星数据,对地球同步轨道(GEO)相对论电子变化进行了统计分析,研究了相对论电子通量(Fe)增强事件的发展过程,探讨了利于相对论电子通量增强的太阳风和地磁活动条件.主要结论如下:(1)GEO相对论电子通量即使是峰值,也具有明显的地方时特性,最大电子通量出现在磁正午时.午/夜电子通量比率随着太阳风速度(Vsw)增加而增大;在Dst-50nT时相对论电子具有规则的地方时变化.在太阳活动下降相,电子通量与各参数的相关性较好,与其相关性最好的Vsw、Kp指数以及三次根号下的太阳风密度(N)分别出现在电子通量前39~57h、57~80h和12~24h.(2)强(日平均电子通量峰值Femax≥104 pfu)相对论电子事件,在距离太阳活动谷年前两年左右和春秋分期间发生率最高,较弱(104Femax≥103 pfu)事件无此特点;大部分强相对论电子事件中,电子通量在磁暴主相开始增加,较弱事件中则在恢复相开始回升.(3)太阳风密度变化对相对论电子事件的发展具有重要指示作用.电子通量在太阳风密度极大值后0~1天达到极小值,太阳风密度极小值后0~2天达到极大值.(4)90%以上相对论电子事件是在磁暴及高速太阳风的条件下发生的,与其伴随的行星际参数和地磁活动指数极值满足以下条件:Vswmax516km/s,Dstmin-31nT,Nmin2.8cm-3,Nmax14.1cm-3,Bzmin-2.9nT,AEmax698nT.(5)磁暴过程中,Dstmin后日平均电子通量大于103 pfu的发生概率为53%左右,强/弱相对论电子事件占总数比例分别为36%/64%左右,磁暴强度对其无影响.磁暴过程中的Vsw、N和AE指数大小对于能否引起相对论电子增强起着指示作用.     

Regional response of the mesosphere–lower thermosphere dynamics over Scandinavia to solar proton events and geomagnetic storms in late October 2003

The short-term regional responses of the mesosphere–lower thermosphere (MLT) dynamics over Scandinavia to the exceptionally strong solar storms with their accompanying solar proton fluxes on the Earth in late October 2003 have been investigated using radar measurements at Andenes (69°N, 16°E) and Esrange (68°N, 21°E). Several solar activity storms resulted in solar proton events (SPEs) at this time, but a particularly active period of high proton fluxes occurred between 28 and 31 October 2003. The significant temperature drop (∼25 K), detected by the meteor radar at Andenes at altitude ∼90 km, was in line with the enhancement of the proton fluxes and was caused by the dramatic reduction of the ozone in the high-latitude middle atmosphere monitored by satellite measurements. This exceptionally strong phenomenon in late October 2003 was composed of three geomagnetic storms, with the first one occurring in the daytime of 29 October and the other two storms in the nighttime of 29 and 30 October, respectively. The responses of the prevailing wind and the main tides (24- and 12-h tides) were studied in detail. It was found that the response of the MLT dynamics to the first geomagnetic storm occurring in the daytime and accompanied by solar proton fluxes is very different from those to the second and third geomagnetic storms with onsets during the nighttime. Some physical mechanisms have been suggested in order to explain the observed short-term variability of the MLT dynamics. This case study revealed the impact of the SPEs observed in late October 2003 and the timing of the geomagnetic storms on the MLT neutral wind responses observed over Scandinavia.     

Polar PWI and CEPPAD observations of chorus emissions and radiation belt electron acceleration: Four case studies

We investigated the role of whistler-mode chorus in accelerating outer radiation belt electrons during four moderate geomagnetic storms when data from the Polar Plasma Wave Investigation (PWI) were available. The storm time periods we examined included two storms associated with coronal mass ejections (CMEs), the well-studied January 10–13, 1997 International Solar Terrestrial Physics event and the May 12–15, 1997 event. We compared these two storms with two geomagnetically active periods that were not associated with CMEs. Although strong chorus emissions were observed during all four events, the association of electron acceleration with chorus emissions is not clear. During all four events, the Polar Comprehensive Energetic Particle and Pitch Angle Distribution (CEPPAD) experiment observed increases in the fluxes of energetic electrons (0.8<E<6.4 MeV). The two events associated with CMEs featured a sudden increase in the electron fluxes above 0.8 MeV that may have been related to the impact of the CME shock wave upon the magnetosphere. The other two events featured more gradual increases in the electron fluxes over a period of several days. The data from these events indicate that the role played by resonant interactions with chorus in accelerating electrons may depend on the upstream solar wind conditions driving the storm.     

中低纬地区电离层对CIR和CME响应的统计分析

本文利用中低纬日本地区(131°E,35°N)GPS-TEC格点化数据,分析了2001—2009年间109个共转相互作用区(CIR)事件、45个日冕物质抛射(CME)事件引起的地磁扰动期间电离层的响应.结果表明,电离层暴的类型随太阳活动的变化而有不同的变化,CIR事件引发的电离层正相暴、正负双相暴多发生在太阳活动下降年,负相暴多发生在高年,负正双相暴多发生在低年;CME事件引发的电离层正相暴和负相暴多发生在高年.CIR和CME引发的不同类型的电离层暴的季节性差异不大,在夏季多发生正负双相暴.电离层暴发生时间相对地磁暴的时延大部分在-6~6h之间,但CIR引发的电离层暴时延范围更广,在-12~24h之间,而CME引发的电离层暴时延主要在-6~6h之间.中低纬的电离层暴多发生在主相阶段,其中CIR引发的双相暴也会发生在初相阶段.电离层负暴多发生在AE最大值为800~1200nT之间.CIR引起的电离层扰动持续时间较长,一般在1~6天左右,而CME引起的电离层扰动持续时间一般在1~4天左右.     

Ionospheric and Solar Wind Variation during Magnetic Storm Onset and Main Phase at Low- and Mid-latitudes

The relationship between the F2-layer critical frequency and solar wind parameters during magnetic storm sudden commencement (SSC) and main phase periods for intense (IS) and very intense (VIS) class of storms is investigated. The analysis covers low- and mid-latitude stations. The effects of ionospheric storm during SSC period is insignificant compared to the main phase, but can trigger the latter. The main phase is characterized by severe negative storm effect at both latitudes during VIS periods while it is latitudinal symmetric for IS observations. The IS reveal positive/negative storm phase in the low-/mid-latitudes, respectively. Ionization density effect is more prominent during VIS events, and is attributed to large energetic particle and solar activity input into the earth magnetosphere. However, ionospheric effect is more significant at the low-latitude than at the mid-latitude. Lastly, ionospheric storm effect during a geomagnetic storm may be related to the combinational effect of interplanetary and geomagnetic parameters and internal ionospheric effect, not necessarily the solar wind alone.     

Solar-wind–magnetosphere coupling,including relativistic electron energization,during high-speed streams

High geomagnetic activity occurs continuously during high-speed solar wind streams, and fluxes of relativistic electrons observed at geosynchronous orbit enhance significantly. High-speed streams are preceded by solar wind compression regions, during which time there are large losses of relativistic electrons from geosynchronous orbit. Weak to moderate geomagnetic storms often occur during the passage of these compression regions; however, we find that the phenomena that occur during the ensuing high-speed streams do not depend on whether or not a preceding storm develops. Large-amplitude Alfvén waves occur within the high-speed solar wind streams, which are expected to lead to intermittent intervals of significantly enhanced magnetospheric convection and to thus also lead to repetitive substorms due to repetitively occurring reductions in the strength of convection. We find that such repetitive substorms are clearly discernible in the LANL geosynchronous energetic particle data during high-speed stream intervals. Global auroral images are found to show unambiguously that these events are indeed classical substorms, leading us to conclude that substorms are an important contributor to the enhanced geomagnetic activity during high-speed streams. We used the onsets of these substorms as indicators of preceding periods of enhanced convection and of reductions in convection, and we have used ground-based chorus observations from the VELOX instrument at Halley station as an indicator of magnetospheric chorus intensities. These data show evidence that it is the periods of enhanced convection that precede substorm expansions, and not the expansions themselves, that lead to the enhanced dawn-side chorus wave intensity that has been postulated to cause the energization of relativistic electrons. If this inference is correct, and if it is chorus that energizes the relativistic electrons, then high-speed solar wind streams lead to relativistic electron flux enhancements because the embedded large-amplitude Alfvén waves give multi-day periods of intermittent significantly enhanced convection.     

Relativistic electron enhancements,magnetic storms,and substorm activity

The relativistic electron fluxes of the Earth's outer radiation belt are subjected to strong temporal variations. The most prominent changes are initiated by fast solar wind streams impinging upon the magnetosphere, which often also cause enhanced substorm activity and magnetic storms. Using 4 years of data from the particle detector REM aboard the UK satellite Strv-1b in a GTO, we investigated the relation between these different appearances of geomagnetic activity. A typical sequence is that there is a drop in the relativistic electron intensity during the main phase of the magnetic storm and a successive enhancement during the recovery phase which sometimes leads to much higher than pre-storm fluxes. Whereas the flux drop is well correlated with the magnetic storm intensity and is mainly due to the deceleration and loss of particles caused by the ring-current-induced magnetic field changes, there is only a bad correlation between the post-storm electron flux and Dst. As we show here, it is much more the level of substorm activity during the whole event which determines the size of the flux enhancements.     

Generation of magnetic field Pc5 pulsations and particle fluxes during the recovery phase of a magnetic storm on October 31, 2003

The spatial structure of intensive Pc5 pulsations of the geomagnetic field and riometer absorption during the recovery phase of a strong magnetic storm that occurred on October 31, 2003, have been considered in detail. The global structure of disturbances has been analyzed based on a global network of magnetometers and riometers supplemented by the data of magnotometers and particle detectors on geostationary satellites GOES and LANL. The local spatial structure was studied by the data of a regional network of Finland vertical riometers and the stations at the IMAGE magnetic network. Quasiperiodic variations in the magnetic field and riometer absorption are generally similar and have a close frequency composition; nevertheless, their local spatial structures are different, as a result of which the concept that riometer absorption pulsations represent a purely modulation process is doubtful. It is assumed that the observed variations are oscillations of two related systems: the magnetospheric MHD waveguide/resonator and systems including cyclotron noise and electrons. Geomagnetic Pc5 oscillations during the recovery phase of a strong magnetic storm supposedly result from the generation of the magnetospheric waveguide on magnetospheric flanks. An analysis of azimuthal propagation phase velocities indicates that these oscillations depend on intramagnetospheric parameters rather than on the solar wind velocity. The magnetospheric waveguide is in a metastable state when solar wind velocities are high, and the quasiperiodic fluctuations of the solar wind pressure stimulate the excitation of the waveguide.     

Injection of relativistic electrons into the internal magnetosphere during magnetic storms: Connection with substorms

The connection between rapid increases in the intensity of electrons with energies >0.3 MeV and magnetospheric substorms was studied for the first time by measurements of energetic electrons on the low-orbit SERVIS-1 satellite. In addition to the well-known process of radial diffusion detected at the recovery phase, the increases during a period of time no longer than 1.5 h at the main phase of six magnetic storms in a channel of 0.3–1.7 MeV (in three of them, in a channel of 1.7–3.4 MeV) were measured. An analysis of auroral zone magnetograms demonstrated that the increases occurred at the instant of magnetospheric substorm activation. A conclusion is made that the increases are caused by the radial injection of electrons by a pulse electric field induced during substorm activations. Pulse injections are shown to be one of the main mechanisms of electron radiation belt completion in the inner magnetosphere and, in combination with moderate radial diffusion, to be responsible for the appearance of large fluxes of energetic electrons (“killers”) in the magnetosphere after magnetic storms.     

Variations in the ULF index of geomagnetic pulsations during strong magnetic storms

The level of wave geomagnetic activity in the morning, afternoon, and nighttime sectors during strong magnetic storms with Dst varying from ?100 to ?150 nT has been statistically studied based on a new ULF wave index. It has been found out that the intensity of geomagnetic pulsations at frequencies of 2–7 mHz during the magnetic storm initial phase is maximal in the morning and nighttime sectors at polar and auroral latitudes, respectively. During the magnetic storm main phase, wave activity is maximal in the morning sector of the auroral zone, and the pulsation intensity in the nighttime sector is twice as low as in the morning sector. It has been indicated that geomagnetic pulsations excited after substorms mainly contribute to a morning wave disturbance during the magnetic storm main phase. During the storm recovery phase, wave activity develops in the morning and nighttime sectors of the auroral zone; in this case nighttime activity is also observed in the subauroral zone.     

磁暴主相期间外辐射带结构的变化

本文利用相对論带电粒子的两个寝渐不变量,討論了磁暴主相期間外輻射带中心結构的变化。作者认为磁暴主相是由“磁暴带”环电流所产生。“磁暴带”假設位于外輻射带中心之外,它是太阳等离子体穿入磁层后形成的。本文对初始能量W=20Kev和W=1Mev的电子分別进行了計算。 結果表明,在磁暴主相期間电子向外漂移,其赤道投擲角減小,但镜点离地面距离增高。因此,主相时所观測到的极光,并不是由于地磁場的平緩下降使小投擲角电子注入大气层而形成的。此外,計数率降低的主要原因是由于力管截面膨胀造成的粒子密度減小以及电子減速,而电子減速与投擲角有关,由此决定了电子通量沿磁力线分布的变化。以上結果与探险者6号（Explorer Ⅵ）的观測一致。     

Estimation of storm-time level of day-side wave geomagnetic activity using a new <Emphasis Type="Italic">ULF</Emphasis> index

The level of wave geomagnetic activity in the morning and daytime sectors of auroral latitudes during strong magnetic storms with Dst _min varying from ?100 to ?150 nT in 1995–2002 have been studied using a new ULF index of wave activity proposed in [Kozyreva et al., 2007]. It has been detected that daytime Pc5 pulsations (2–6 mHz) are most intense during the main phase of a magnetic storm rather than during the recovery phase as was considered previously. It has been indicated that morning geomagnetic pulsations during the substorm recovery phase mainly contribute to daytime wave activity. The appearance of individual intervals with the southward IMF B _z component during the magnetic storm recovery phase results in increases in the ULF index values.     

磁暴期间辐射带电子相空间密度的多卫星联合观测

地球外辐射带是一个高度动态变化的空间环境,辐射带电子通量的变化在磁暴期间尤为明显.要分析潜在的电子动态变化机制,需要排除绝热效应产生的影响.在以三个绝热不变量组成的相空间坐标中,利用相空间密度(PSD)可以反映电子的真实加速和损失情况.本文详细分析两颗范艾伦卫星和三颗GPS导航卫星在2013年3月的同步电子通量观测数据,发现在3月17日磁暴期间,当太阳风动压增大、行星际磁场南向时,辐射带电子通量会发生骤降.进一步将电子通量转换成电子相空间密度并利用不同第一、第二绝热不变量(μ,K)组合条件下PSD径向分布的差异性,深入探究磁暴期间辐射带电子的动态变化机制.结果表明:磁暴初期由于电子的局地加速导致PSD不断上升;磁暴主相期间,由于磁层顶阴影效应以及伴随的向外径向扩散损失导致PSD快速降低;位于不同空间位置的多颗卫星观测为明晰辐射带电子动态物理过程提供了重要的便利.     

Precipitation of energetic magnetospheric electrons and accompanying solar wind characteristics

From 1957 up to the present time, the Lebedev Physical Institute (LPI) has performed regular monitoring of ionizing radiation in the Earth’s atmosphere. There are cases when the X-ray radiation generated by energetic magnetospheric electrons penetrates the atmosphere and is observed at polar latitudes. The vast majority of these events occurs against the background of high-velocity solar wind streams, while magnetospheric perturbations related to interplanetary coronal mass ejections (ICMEs) are noneffective for precipitation. It is shown in the paper that ICMEs do not cause acceleration of a sufficient amount of electrons in the magnetosphere. Favorable conditions for acceleration and subsequent scattering of electrons into the loss cone are created by magnetic storms with an extended recovery phase and with sufficiently frequent periods of negative Bz component of the interplanetary magnetic field (IMF). Such geomagnetic perturbations are typical for storms associated with high-velocity solar wind streams.     

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.