作者机构：
[周庆华; 杨昶; 贺艺华; 刘斯; 周晓萍; 唐立军; 肖伏良] School of Physics and Electronic Sciences,Changsha University of Science and Technology
会议名称：
中国空间科学学会空间物理学专业委员会第十五届全国日地空间物理学研讨会
会议时间：
2013-01-01
会议地点：
中国湖北十堰
会议论文集名称：
中国空间科学学会空间物理学专业委员会第十五届全国日地空间物理学研讨会摘要集
摘要：
A ray tracing study of electromagnetic ion cyclotron（EMIC）waves is conducted by incorporation of a realistic plasma density model.The simulation result shows that EMIC waves propagate away from the equatorial source region to higher latitudes basically along geomagnetic field lines,and are reflected at the region where their frequency locally matches the bi-ion frequency.H+band waves suffer H+-He+bi-ion frequency reflection at lower latitudes,whereas He+band waves suffer He+-O+bi-ion frequency reflection at higher latitudes.Moreover,the concentration of heavy ions determines the bi-ion frequencies and then determines the reflection location of ray paths of EMIC waves.The current results present a first detailed study on the propagation characteristics of EMIC waves associated with bi-ion frequencies.
关键词：
electromagnetic ion cyclotron waves;cold electron heating;THEMIS observation
摘要：
[1] A cold electron heating event associated with electromagnetic ion cyclotron (EMIC) waves is observed and modeled. The observational data of particles and waves are collected by the Time History of Events and Macroscale Interactions during Substorms spacecraft at magnetic local time 17.0–17.2. During this event, intense He+ band EMIC waves with the peak frequency 0.25 Hz are excited, corresponding to the observed phase space density (PSD) of distinct anisotropic ions. Meanwhile, substantial enhancements in energy flux of cold (1–10 eV) electrons are observed in the same period. The energy flux of electrons below 10 eV is increased by several to tens of times. We use a sum of kappa distribution components to fit the observed ion PSD and then calculate the wave growth rate driven by the anisotropic hot protons. The calculated result is in good agreement with the in situ observation. Then, we investigate whether the excited EMIC waves can transfer energy to cold electrons by Landau resonant absorption and yield electron heating. Using the typical Maxwellian distribution for cold electrons, we evaluate the wave damping rates resulted from the cold electrons in gyroresonance with EMIC waves. The simulating results show that the strong wave growth region in the He+ band induced by anisotropic ions corresponds to the strong wave damping region driven by cold electrons. Moreover, cold electrons can be heated efficiently at large wave normal angles. The current results provide a direct observational evidence for EMIC-driven cold electron heating—a potential mechanism responsible for stable auroral red arc.
作者机构：
[谢海情; 唐立军; 文勇军] School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha, 410004, China;[彭平; Zeng Y.] School of Physics and Microelectronics Science, Hunan University, Changsha, 410082, China
通讯机构：
[Tang, L.] S;School of Physics and Electronic Science, Changsha University of Science and Technology, China
摘要：
Electromagnetic ion cyclotron (EMIC) waves are excited near the magnetic equator by anisotropic ring current ions with energies near a few tens of keV. We investigate the instability and the path-integrated gain of EMIC waves during wave propagation. Calculations are performed by a global core density model, a field-aligned density model and particularly the hot ring current ions modeled by a kappa distribution. Simulating results show that the instability of EMIC waves is influenced primarily by the parameters of hot ring current ions, the wave normal angle and the composition of background plasma. A larger path-integrated gain occurs when the initial wave vector points toward lower L shells. During the storm main phase, the most common EMIC wave is the He+ band wave which occurs in the outer magnetosphere beyond the plasmapause with frequency just below the cyclotron frequency of He+. During the recovery phase, EMIC wave occurs in H+ band and He+ band with almost the same intensity in cases of interest. The O+ band EMIC waves are very weak and quite rare. This result presents a further insight into propagation and instability of EMIC waves under different geomagnetic activities.
摘要：
The contributions of dayside and nightside gyroresonance of chorus waves to electron radiation belt evolution at L = 6.6 are detailedly differentiated via fully solving the two-dimensional Fokker-Plank equation. The numerical results show that the chorus waves at different regions play significantly different roles. The dayside chorus waves can cause obvious loss of energetic electrons at lower pitch angles and weak energization at larger pitch angles. The nightside chorus waves can yield significant energization at larger pitch angles, but cannot efficiently resonate with the energetic electrons at lower pitch angle. Due to the numerical difficulty in fully solving Fokker-Planck equation, the cross diffusion terms are often ignored in the previous work. Here the effect of cross diffusion at different regions is further analyzed. On the dayside, ignoring cross diffusion overestimates the electron phase space density by several orders of magnitude at lower pitch angles, and consequently the dayside chorus waves are incorrectly regarded as an effective energization mechanism. On the nightside, ignoring cross diffusion overestimates the electron phase space density (PSD) by about one order of magnitude at larger pitch angles. These numerical results suggest that cross diffusion terms can significantly affect gyroresonance of chorus waves on both the dayside and nightside, which should be included in the future radiation belt models.
关键词：
MLT distribution;magnetosonic waves;radiation belts;three-dimensional ray tracing
摘要：
[1] A three dimensional ray tracing of fast magnetosonic (MS) waves is first performed by using a global core density model and a field-aligned density model. Simulating results show that MS waves are primarily confined within a few degrees of the geomagnetic equator due to magnetospheric reflection. MS waves originating from different L-shells on the dayside can propagate either into or out of the plasmasphere through the plasmapause. In particular, MS waves can propagate eastward (later MLT) or westward (earlier MLT) over a broad region of MLT. The current results further reveal a variety of propagation characteristics, particularly important for the MLT distribution of MS waves.
