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Влияние рекуррентных высокоскоростных потоков солнечного ветра на формирование структуры энергетических спектров электронов на геостационарной орбите
The authors have performed quantitative measurements to evaluate effects of solar wind speed and density on energy spectra structure of electron fluxes in the Earth’s outer radiation belt (EORB) shaped in 2007. The research has been conducted considering sufficiently isolated high speed solar wind (SW) fluxes. In 2007, 29 electron flux rises were registered in which fluxes of relativistic electrons of ~ 2 MeV were observed. The study analyzes data obtained from the LANL–GEO Satellite (electron energy range of 24.1–2000 keV) and SW parameters of the OMNI data base. Plasma density at the leading edge of SW high speed flux served as evaluation parameter of the study. For each of 29 electron flux rises, dependence of maximum differential electron fluxes characteristics was separately analyzed vs speed and density of SW. Electron fluxes have been analyzed, considering three SW density ranges (4–6, 6–12 & 13–21 cm-3) for electron flux vs SE speed relations, and three SW speed ranges (400–535, 535–602 & 602–668 km/s) for electron flux vs SW density relations. Statistical analysis served as a basis to distinguish three electron energy ranges (< 100 keV, 100–500 keV) and relativistic electrons of (> 625 keV) for which significant changes of electron fluxes dynamics have been registered with changing SW speed and density. And particularly it has been demonstrated that electron fluxes of ~ 100– 500 keV (seed particles) scarcely depend on SW speed and density variations. This energy area has a clearly defined top limit of ~ 500 keV electrons energy. Outside GEO, 100–500 keV electrons accelerate to 500 keV on average and form an outer source for GEO. According to our data, electron flux characteristics come over from being nearly independent on SW parameters to abruptly changing (> 625 keV) depending on SW speed and density only at an electron energy of ~ 500 keV. This value defines the actual lower limit of local resonant seed electron acceleration produced by ultralow frequency waves (ULF waves) at L ~ 5 (L is McIlwain L-parameter; e.g., magnetic shell L = 6 is 6R3 away from the Earth’s center in the plane of geomagnetic equator, where R3 is the Earth’s radius) to relativistic energies. Results of our study based on the EORB electron fluxes dynamics vs SW speed and density analysis have been proved in many other studies of phase density dynamics in the EORB electron fluxes. Analysis of electron energy spectra provided quantitative estimation of SW speed and density effects on formation of relativistic electron fluxes in the EORB. The analysis provided the following results: 1) reduction of electron flux with increasing of SW plasma density at a constant SW speed; 2) increasing of density effect with increasing of SW speed, the effect can be registered at a speed of ≤ 650 km/s; 3) at geostationary orbit, at SW speed of > 660 km/s and SW plasma density of СВ > 8 cm3, high energy electron fluxes are virtually independent on SW density. The obtained results demonstrate complex balance between acceleration processes and losses resulting from interaction of electrons with ultralow frequency (ULF) and ion cyclotron (EMIC) waves. Increasing of SW plasma density causes significant power rise of EMIC-waves, which basically define speed of electron pitch-angle diffusion into the loss cone, being the maximum for relativistic electrons.