摘要
波粒相互作用是环电流损失的重要机制之一,但波粒相互作用导致的环电流离子沉降而损失迄今为止缺乏直接的观测证据.基于磁层及电离层卫星的协同观测,本文报道了发生在2015年9月7日,由电磁离子回旋波(EMIC波)导致环电流质子沉降的共轭观测事件.在等离子体层的内边界,Van Allen Probe B卫星观测到,存在EMIC波的区域和不存在EMIC波的区域相比,离子通量的投掷角分布的各向异性变弱.我们将Van Allen Probe B卫星沿着磁力线投影到电离层高度,同时在该投影区域内DMSP 16卫星在亚极光区域观测到环电流质子沉降.而且,通过从理论上计算质子弹跳平均扩散系数,我们进一步证实观测的EMIC波确实能将环电流质子散射到损失锥中.本文的研究工作为EMIC波导致环电流质子沉降提供了直接的观测证据,揭示了环电流衰减的重要物理机制:EMIC波将环电流质子散射到损失锥中,从而沉降到低高度大气层中而损失.
Wave-particle interaction is considered as an important mechanism for the loss of ring currents.However,the direct observational proof of the loss of ring currents caused by wave-particle interaction has not been reported so far.Based on the combination of observations from magnetosphere to ionosphere,this paper presents conjugated observations of ring current(RC)proton precipitation caused by electromagnetic ion cyclotron(EMIC)waves on September 7,2015.In the inner boundary of the plasmasphere,the Van Allen Probe B satellite observed that the ion flux anisotropy of pitch angle distributions was weaker in the region where the EMIC wave existed than the region where the EMIC wave did not appear.While at ionospheric altitudes,the DMSP 16 satellite at the footprint of the Van Allen probe B simultaneously observed the RC proton precipitation.In addition,we demonstrate that observed EMIC waves can truly scatter RC ions into the loss cone through theoretically calculating the pitch angle diffusion coefficients for protons.Our result provides a direct proof of precipitation of ring current protons caused by EMIC waves so as to reveal the important mechanism for the loss of ring currents,i.e.,EMIC waves can scatter ring current ions into the loss cone and lead to the precipitation and loss of ring current ions in the low-altitude atmosphere.
作者
王杰
袁志刚
余雄东
薛祖祥
WANG Jie;YUAN ZhiGang;YU XiongDong;XUE ZuXiang(School of Electronic Information,Wuhan University,Wuhan 430072,China)
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2020年第6期2131-2140,共10页
Chinese Journal of Geophysics
基金
国家自然科学基金(41874194,41374168,41521063)资助.
关键词
电磁离子回旋波
环电流质子
能量质子沉降
波粒相互作用
EMIC waves
Ring current protons
Energetic proton precipitation
Wave-particle interaction
