地球輻射帶動(dòng)態(tài)變化和輻射帶粒子快速加速研究

宗秋剛

摘要：通過SAMPEX衛(wèi)星的觀測(cè)，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(fā)現(xiàn)外輻射帶的內(nèi)、外邊界都可以被隨著L 殼指數(shù)衰減的函數(shù)很好地?cái)M合出來。另外，本報(bào)告根據(jù)這一指數(shù)衰減函數(shù)和由此得到的動(dòng)態(tài)的外輻射帶內(nèi)、外邊界改進(jìn)了RBC指數(shù)的計(jì)算，并由此得到，CME磁暴有可能比CIR磁暴產(chǎn)生更多的相對(duì)論電子。 輻射帶物理模型STEERB基于三維的Fokker-Planck方程實(shí)現(xiàn)， 包含局地波粒相互作用、徑向擴(kuò)散和絕熱輸運(yùn)等物理過程. 由于數(shù)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(guān)的交叉擴(kuò)散項(xiàng). STEERB模型的對(duì)比實(shí)驗(yàn)顯示， 交叉擴(kuò)散項(xiàng)的忽略能夠?qū)е码娮油勘桓吖?倍甚至幾個(gè)數(shù)量級(jí). 這個(gè)結(jié)果說明， 交叉擴(kuò)散項(xiàng)對(duì)于輻射帶電子通量的準(zhǔn)確評(píng)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(chǎng)， 忽略了背景磁場(chǎng)變化引起的絕熱過程. STEERB模型則采用了時(shí)變的背景磁場(chǎng)，同時(shí)引入絕熱和非絕熱過程. 對(duì)比實(shí)驗(yàn)結(jié)果顯示， 絕熱輸運(yùn)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(nèi)磁層激發(fā)ULF波；激發(fā)的極性模ULF波會(huì)造成“殺手”電子的快速加速過程。極向模和環(huán)向模ULF波對(duì)漂移-共振加速的作用在不同L值區(qū)域有所不同。環(huán)向模ULF 波對(duì)能量電子的加速在L值較大的區(qū)域（外磁層）較為重要， 而在L值較小的區(qū)域（內(nèi)磁層）， 極向模ULF波則對(duì)能量電子的加速起主要作用。

關(guān)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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