地球輻射帶動態變化和輻射帶粒子快速加速研究

宗秋剛

摘要：通過SAMPEX衛星的觀測，定量地研究了在CME和CIR磁暴期間1.5-6.0MeV“殺手”電子的通量分布的變化。發現外輻射帶的內、外邊界都可以被隨著L 殼指數衰減的函數很好地擬合出來。另外，本報告根據這一指數衰減函數和由此得到的動態的外輻射帶內、外邊界改進了RBC指數的計算，并由此得到，CME磁暴有可能比CIR磁暴產生更多的相對論電子。 輻射帶物理模型STEERB基于三維的Fokker-Planck方程實現， 包含局地波粒相互作用、徑向擴散和絕熱輸運等物理過程. 由于數值格式的限制， 以往的輻射帶模型均沒有引入局地波粒相互作用相關的交叉擴散項. STEERB模型的對比實驗顯示， 交叉擴散項的忽略能夠導致電子通量被高估5倍甚至幾個數量級. 這個結果說明， 交叉擴散項對于輻射帶電子通量的準確評估具有重要意義. 以往的輻射帶物理模型常常采用固定的偶極磁場， 忽略了背景磁場變化引起的絕熱過程. STEERB模型則采用了時變的背景磁場，同時引入絕熱和非絕熱過程. 對比實驗結果顯示， 絕熱輸運過程能夠顯著地影響輻射帶電子通量的演化. 行星際激波與磁層的相互作用能夠在內磁層激發ULF波；激發的極性模ULF波會造成“殺手”電子的快速加速過程。極向模和環向模ULF波對漂移-共振加速的作用在不同L值區域有所不同。環向模ULF 波對能量電子的加速在L值較大的區域（外磁層）較為重要， 而在L值較小的區域（內磁層）， 極向模ULF波則對能量電子的加速起主要作用。

關鍵詞：輻射帶；“殺手電子”；CME磁暴；CIR磁暴；波粒相互作用；ULF波；VLF波

Dynamic Variation and the Fast Acceleration of Particles in Earths Radiation Belt

Abstract：We have quantitatively studied the radiation belt electrons variations. It is found that the boundaries determined by fitting an exponential to the flux as a function of L shell obtained in this study agree with the observed outer and inner boundaries of the outer radiation belt. Furthermore， we have constructed the Radiation Belt Content （RBC） index by integrating the number density of electrons between those inner and outer boundaries. According to the ratio of the maximum RBC index during the recovery phase to the pre-storm average RBC index， we conclude that CME-driven storms produce more relativistic electrons than CIR-driven storms in the entire outer radiation belt， although the relativistic electron fluxes during CIR-related storms are much higher than those during CME-related storms at geosynchronous orbit. The physical radiation belt model STEERB is based on the three-dimensional Fokker-Planck equation and includes the physical processes of local wave-particle interactions， radial diffusion， and adiabatic transport. The physical radiation belt model STEERB is based on the three-dimensional Fokker-Planck equation and includes the physical processes of local wave-particle interactions， radial diffusion， and adiabatic transport. The numerical experiments of STEERB have shown that the energetic electron fluxes can be overestimated by a factor of 5 or even several orders （depending on the pitch angle） if the cross diffusion term is ignored. This implies that the cross diffusion term is indispensable for the evaluation of radiation belt electron fluxes. Formal radiation belt models often adopt dipole magnetic field； the time varying Hilmer-Voigt geomagnetic field was adopted by the STEERB model， which self-consistently included the adiabatic transport process. The test simulations clearly indicate that the adiabatic process can significantly affect the evolution of radiation belt electrons. The interactions between interplanetary shocks and magnetosphere can excite ULF waves in the inner magnetosphere； the excited polodial mode ULF wave can cause the fast acceleration of "killer electrons". The acceleration mechanism of energetic electrons by poloidal and toroidal mode ULF wave is different at different L shells. The acceleration of energetic electrons by the toroidal mode ULF waves becomes important in the region with a larger L shell； in smaller L shell regions， the poloidal mode ULF becomes responsible for the acceleration of energetic electrons.

Keywords：Radiation belt； killer electrons； CME magnetic storm； CIR magnetic storm； wave-particle interaction； ULF wave； VLF wave

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