Outer radiation belt of relativistic electrons during the minimum of the 23rd solar cycle

The data on fluxes of electrons with energy Ee > 1 MeV and on radiation doses under the Al shielding of about 2 g/cm² measured on the GLONASS satellite (circular orbit with altitude 20000 km and inclination 65°) for the period from December 2006 through May 2010 are analyzed. The minimum of the 23rd solar cycle turned out to be the longest for all over the space exploration age. Consequently, average semiannual electron fluxes and daily radiation doses are showing the decrease by more than an order of magnitude in comparison with the levels observed in 2007. We present an example of a diffusion wave of relativistic electrons; the wave develops in a period between magnetic storms. This process may result in a significant increase of the radiation dose measured in the orbit, even under the conditions of weak geomagnetic disturbances. The dynamics of variations in relativistic electron fluxes during the magnetic storm of April 5?C6, 2010, is discussed so far as this is the first strong flux enhancement in the 24th solar cycle.     

Verification of magnetic field models based on measurements of solar cosmic ray protons in the magnetosphere

Measurements of solar cosmic ray (SCR) protons in the magnetosphere can be used to verify models of the Earth’s magnetic field. The latitudinal profiles of precipitating SCRs with energies of 1–90 MeV were measured on the CORONAS-F low-orbiting satellite during a strong magnetic storm on October 29–30, 2003. A flux of precipitating protons can remain equal to the interplanetary flux only due to a strong pitch angle diffusion that originates when the radius of the field line curvature is close to that of the particle rotation Larmor radius. The observed boundaries of the strong diffusion region can be compared with the boundaries anticipated according to the models of the magnetic field of the Earth’s magnetosphere. The adiabaticity parameter values, calculated for several instants of the CORONAS-F satellite pass based on the TS05 and parabolic models, do not always correspond to measurements. How possible changes in the model configurations of the magnetic field can allow us to eliminate discrepancies with the experiment and to explain why solar protons with energies of several megaelectronvolts penetrate deep in the Earth’s inner magnetosphere is considered here.     

Arrival of the first relativistic solar protons and conditions in the solar corona

When solar cosmic rays (SCRs) can be observed with ground-based equipment (ground-level enhancements, GLEs), events are often characterized by a rapid increase in the relativistic proton intensity during the initial phase, which makes it possible to estimate the time of particle escape from the solar corona. This phase attracts attention of researchers owing to its closeness in time to the instant of particle acceleration. It is known that the observed SCR characteristics bear traces of many physical processes, including different acceleration mechanisms the relative role of which is still unclear. Flare processes and acceleration by a shock, related to coronal mass ejection (CME), are the main pretenders to the role of SCR accelerator. Several powerful solar proton events during cycle 23 are considered in the work, and the release time of the first particles from the corona and the dynamics of CMEs have been estimated. The time series of the X-ray and radio bursts, close in time to particle escape, are analyzed. The conclusion have been drawn that the first relativistic particles were most probably accelerated during flare processes.     

Deformation of the magnetosphere and the penetration boundary of solar protons before the onset of the main phase of a magnetic storm

The ring current is conventionally considered responsible for the shift of the boundary of solar proton penetration into the inner Earth’s magnetosphere during magnetic storms. The cases of a boundary shift were observed in some works on the dark side before the onset of a magnetic storm, i.e., at positive values of the Dst index. In this work, this type of shift of the penetration boundary is considered in detail with two storms as examples. It is shown that the corresponding distortion of the magnetosphere configuration is induced by an increase in the solar wind pressure during the initial phase of a magnetic storm. The current induced in this case on the magnetopause is closed by a current in the equator plane, which changes the configuration of the dark side of the inner magnetosphere, weakens the magnetic field, and allows solar protons to penetrate the inner magnetosphere. The significant difference in the positions of the penetration boundary and the boundary found from models of the magnetosphere magnetic field can be explained by insufficient consideration of closing currents.     

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.     

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.     

基于Fortran语言的地球外辐射带电子三维数据同化建模

开发地球电子辐射带的数据同化模型, 对于理解辐射带电子的动态演化过程和辐射带空间天气预报具有重要意义.结合范阿伦卫星的辐射带电子观测数据和外辐射带三维扩散模型, 采用卡尔曼滤波算法, 本文开发了基于Fortran语言的外辐射带电子三维数据同化模型(Three-dimensional Data Assimilative Model of Outer Radiation belt Electrons, 简称TDAMORE), 实现对L^*=3~7、能量范围为0.1~5 MeV、投掷角范围为5°~90°的外辐射带电子时空变化过程的三维重构.通过对2018年8月期间外辐射带电子通量演化过程的重构, 证实TDAMORE模型可以较好地重现不同能量和不同投掷角电子通量在磁暴前后的演化特征.通过分析电子通量的观测和同化结果之间的相关系数、平均误差、平均绝对误差和均方误差, 发现对于能量低于4 MeV的电子, 观测与同化结果之间的相关系数基本大于0.8且误差相对较低.而对于更高能量的电子, 观测与同化结果之间的误差相对较高, 这可能是同化模型忽略了电磁离子回旋波对电子的散射损失导致的.

     

Oscillations of galactic cosmic rays and solar indices before the arrival of relativistic solar protons

Using modern wavelet analysis techniques, we have made an attempt to search for oscillations of intensity of galactic cosmic rays (GCR), sunspot numbers (SS) and magnitudes of coronal index (CI) implying that the time evolution of those oscillations may serve as a precursor of Ground Level Enhancements (GLEs) of solar cosmic rays (SCR). From total number of 70 GLEs registered in 1942–2006, the four large events — 23 February 1956, 14 July 2000, 28 October 2003, and 20 January 2005 — have been chosen for our study. By the results of our analysis, it was shown that a frequency of oscillations of GCR decreases as time approaches to the event day. We have also studied a behaviour of common periodicities of GCR and SCR within the time interval of individual GLE. The oscillations of GLE occurrence rate (OR) at different stages of the solar activity (SA) cycle is of special interest. We have found some common periodicities of SS and CI in the range of short (2.8, 5.2, 27 and 60 days), medium (0.3, 0.5, 0.7, 1.3, 1.8 and 3.2 years) and long (4.6 and 11.0 years) periods. Short and medium periodicities, in general, are rather concentrated around the maxima of solar cycles and display the complex phase relations. When comparing these results with the behaviour of OR oscillations we found that the period of 11 years is dominating (controlling); it is continuous over the entire time interval of 1942–2006, and during all this time it displays high synchronization and clear linear ratios between the phases of oscillations of η, SS and CI. It implies that SCR generation is not isolated stochastic phenomena characteristic exclusively for chromospheric and/or coronal structures. In fact, this process may have global features and involve large regions in the Sun’s atmosphere.     

Experimental evidence for direct penetration of ULF waves from the solar wind and their possible effect on acceleration of radiation belt electrons

The event of March 12–19, 2009, when a moderately high-speed solar wind stream flew around the Earth’s magnetosphere and carried millihertz ultralow-frequency (ULF) waves, has been analyzed. The stream caused a weak magnetic storm (D _{st min} = −28 nT). Since March 13, fluxes of energetic (up to relativistic) electrons started increasing in the magnetosphere. Comparison of the spectra of ULF oscillations observed in the solar wind and magnetosphere and on the Earth’s surface indicated that a stable common spectral peak was present at frequencies of 3–4 mHz. This fact is interpreted as evidence that waves penetrated directly from the solar wind into the magnetosphere. Possible scenarios describing the participation of oscillations in the acceleration of medium-energy (E > 0.6 MeV) and high-energy (E > 2.0 MeV) electrons in the radiation belt are discussed. Based on comparing the event with the moderate magnetic storm of January 21–22, 2005, we concluded that favorable conditions for analyzing the interaction between the solar wind and the magnetosphere are formed during a deep minimum of solar activity.     

Dynamics of the radiation belt formed by solar protons during magnetic storms

Experimental proofs of the existence of the formation and destruction mechanisms of solar proton belts in the inner magnetosphere at a rapid change in the penetration boundary of solar protons are presented. An analysis of the measurements of solar protons and alpha-particles on board the Coronas-F low-altitude polar satellite during the magnetic storms in October–November 2003 is performed. During this period, formation and destruction of the belts of solar cosmic rays was observed several times. The compression of the magnetosphere during a storm makes possible the direct penetration of solar protons deep into the inner magnetosphere. The proton trajectories outside the penetration boundary are open, and the preliminary captured particles can easily leave the magnetosphere. During the recovery of the magnetospheric configuration, when the penetration boundary goes away from the Earth, the solar protons and alpha-particles with relatively low velocity of the magnetic drift remain stably captured, whereas the particles of higher energies follow the motion of the penetration boundary. That is why the energy range of the captured protons is limited from above in contrast to the effect of injection during ineffective SC in the low-energy region.     

Magnetohydrodynamics (MHD) numerical simulations on the interaction of the solar wind with the magnetosphere: A review

The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. MHD simulations started at the end of the 1970s, and the initial study was limited to two-dimensional (2D) cases. Due to the intrinsic three-dimensional (3D) characteristics of the geospace, 3D MHD simulations emerged in the 1980s, in an attempt to model the large-scale structures and fundamental physical processes in the magnetosphere. They started to combine with the space exploration missions in the 1990s and make comparisons with observations. Physics-based space weather forecast models started to be developed in the 21st century. Currently only a few space-power countries such as USA and Japan have developed 3D magnetospheric MHD models. With the rapid advance of space science in China, we have developed a new global MHD model, namely PPMLR-MHD, which has high order spatial accuracy and low numerical dissipation. In this review, we will briefly introduce the global 3D MHD modeling, especially the PPMLR-MHD code, and summarize our recent work based on the PPMLR-MHD model, with an emphasis on the interaction of interplanetary shocks with the magnetosphere, large-scale current systems, reconnection voltage and transpolar potential drop, and Kelvin-Helmholtz (K-H) instability at the magnetopause.     

Response of the inner and outer magnetosphere to solar wind density fluctuations during the recovery phase of a moderate magnetic storm

We examine the geomagnetic field and space plasma disturbances developing simultaneously in the solar wind, in the inner and outer magnetosphere, and on the ground from 0730 to 2030 UT on April 11, 1997 during the recovery phase of a moderate magnetic storm. The fluctuations of the solar wind density, H-component of the geomagnetic field, and power of Pc1–2 (0.1–5 Hz) waves at middle and low latitudes evolve nearly simultaneously. These fluctuations also match very well with variations of density and flux of the magnetospheric plasma at the geosynchronous orbit, and of the geomagnetic field at the geosynchronous orbit and northern polar cap. The time delay between the occurrence of disturbances in different magnetosphere regions matches the time of fast mode propagation. These disturbances are accompanied by the generation of Pc1–2 waves at mid- and high-latitude observatories in nearly the same frequency range. A scenario of the evolution of wave phenomena in different magnetospheric domains is proposed.     

>0.3 MeV高能电子注入辐射带槽区事件的分析与预报

本文利用低高度太阳同步轨道系列卫星NOAA/POES从1996年到2006年的>0.3 MeV高能电子观测数据,分析了>0.3 MeV高能电子注入辐射带槽区的特征,研究了注入槽区事件与行星际条件、太阳活动和地磁扰动之间的联系.研究表明>0.3 MeV高能电子注入辐射带槽区事件与磁暴的发生密切相关,注入事件的发生与太阳活动的强度有一定的相关性.在此研究的基础上,本文通过分析辐射带槽区>0.3 MeV高能电子通量和Dst指数的相关性,提出了利用Dst指数推算辐射带槽区>0.3 MeV高能电子通量的方法,继而给出了可行的辐射带槽区高能电子辐射环境的预警模式.     

Solar proton increases and dynamics of the electron outer radiation belt during solar events in December 2006

Increases in solar protons and variations in the electron and proton fluxes from the outer radiation belt are studied based on the GLONASS satellite measurements (the circular orbit at an altitude of ～20000 km with an inclination of ～65°) performed in December 2006. Indications in the channels, registered protons with energies of Ep = 3–70 MeV and electrons with energies of Ee > 0.04 and >0.8 MeV, are analyzed. The data on electrons with Ee = 0.8–1.2 MeV, measured on the Express-A3 geostationary satellite, are also presented. Before the strong magnetic storm of December 14 (|Dst|_max = 146 nT), the maximum of the outer belt electrons with the energy >0.7 MeV was observed at L ～ 4.5. After the storm, the fluxes of these electrons increased by more than an order of magnitude as compared to the prestorm level, and the maximum of a “new” belt shifted to L < 4 (minimal L reached by the GLONASS orbit). Under quiet geomagnetic conditions, solar protons with the energies >3 MeV fill only high-latitude legs of the GLONASS orbit. During the strong magnetic storm of December 15, the boundary of proton penetration into the magnetosphere almost merged with the orbital maximum of the proton radiation belt.     

Solar wind—magnetosphere coupling: A review of recent results

This paper reviews some aspects of solar wind–magnetosphere–ionosphere interaction. It is shown that in addition to the interplanetary electric field, the solar wind dynamic pressure also has a significant role in determining the state, dynamics, and energetics of the system. It is demonstrated how the state of the magnetosphere and the prior driving affect the amount of energy input to the system, which highlights the capability of the magnetosphere to control the energy flow. The active role of the magnetosphere in determining the dynamics is illustrated by statistical results of the flux balance in the magnetotail and the various dynamic cycles the system can enter. The inner magnetosphere processes during storms are shown to be a result of a complex interplay of processes at the magnetopause and in the magnetotail in response to the solar wind driving. The conclusions are drawn from statistical observational results, empirical models, and global MHD simulations.     

Diagnostics of solar wind streams and their sources in the solar corona

The studies are based on the experimental mass sounding of the interplanetary plasma near the Sun at radial distances of R = 4−70 R _S, performed at Pushchino RAO, Russian Academy of Sciences, and on the calculated magnetic fields in the solar corona based on the magnetic field strength and structure measured on the Sun’s surface at J. Wilcox Solar Observatory, United States. The experimental data make it possible to localize the position of the boundary closest to the Sun of the transition transonic region of the solar wind in the near-solar space (R ≈ 10−20 R _S) and to perform an interrelated study of the solar wind structure and its sources, namely, the magnetic field components in the solar corona based on these data. An analysis of the evolution of the flow types in 2000–2007 makes it possible to formulate the physically justified criterion responsible for the time boundaries of different epochs in the solar activity cycle.     

Dependence of the power consumed by the magnetosphere on the solar wind parameters

The results of the previous studies, where the expressions were obtained for the electric current, which is generated at the bow shock front and is closed through the magnetosphere, and for the magneto-pause potential as a function of such solar wind parameters as the plasma density and velocity and the IMF intensity, are used. The power (W) consumed by the magnetosphere is equal to the Poynting vector flux S through the magnetopause. According to the special case of the Poynting theorem applied by Heikkila to the-magnetosphere, the energy flux can be expressed in terms of the electric potential (the integration is carried out over the entire surface of the magnetosphere). As a result, the required dependence, which is quadratic with respect to the IMF B _z component, has been obtained for W. It is discussed why the magnetosphere is energy-isolated at the northward IMF B _z component despite this.     

Latest progress on interactions between VLF/ELF waves and energetic electrons in the inner magnetosphere

Interactions between very/extremely low frequency (VLF/ELF) waves and energetic electrons play a fundamental role in dynamics occurring in the inner magnetosphere. Here, we briefly discuss global properties of VLF/ELF waves, along with the variability of the electron radiation belts associated with wave-particle interactions and radial diffusion. We provide cases of electron loss and acceleration as a result of wave-particle interactions primarily due to such waves, and particularly some preliminary results...