基于Van Allen Probes EMFISIS波动仪器观测的内磁层下频带哨声合声波全球分布的统计分析

A statistical analysis of the global distribution of inner magnetospheric lower-band chorus waves based on Van Allen Probes EMFISIS observations

基于Van Allen Probes近三年的EMFISIS仪器波动观测数据,对内磁层下频带哨声模合声波幅度的全球分布特性对地磁活动水平的依赖性进行了详细的统计分析,着重研究下频带合声波平均场强幅度随磁壳值L、磁地方时、地磁纬度的分布特征及不同强度区间的合声波的发生概率.结果表明,下频带合声波的波动强度与地磁活动密切正相关,处于强磁扰期间的合声波具有更大的振幅,其发生率与地磁活动强度具有同样的正相关特性.下频带合声波主要发生于午夜至下午的磁地方时区间,其余的磁地方时时段下频带合声波较弱.赤道面附近的下频带合声波主要分布在夜侧至黎明这一时段内,随着磁纬度的增加逐步向日侧扩展.下频带合声波在午夜侧(21-03 MLT)主要出现在15°的磁纬范围内,在晨侧(03-09 MLT)可以到达15°磁纬甚至更高纬度.下频带合声波主要发生于L=~4.5的附近区域.随着地磁活动的增加,下频带合声波所覆盖的L-shell空间区域增大,趋势为向高、低L值区域同时扩展.建立的下频带哨声合声波的全球分布模型将有助于进一步深入理解该重要磁层波动对辐射带电子的波粒作用散射效应和对辐射带动力学过程的定量贡献.

Based on the nearly three-year wave data from the EMFISIS instrument onboard the Van Allen Probes, a statistical analysis of the global distribution of inner magnetospheric lowerband chorus is performed in detail with respect to the level of geomagnetic activity. The emphasis is placed on the quantitative variations of average lower-band chorus wave amplitude with L shell, magnetic local time （MLT） and geomagnetic latitude and the occurrence pattern of lower- band chorus waves at different amplitude levels. The results indicate that there exists a strong positive correlation between the average wave amplitude and the geomagnetic activity level. The lower-band chorus intensifies with increasing geomagnetic activity. The occurrence rates of lower- band chorus also tend to increase when the geomagnetic condition intensifies. Lower-band chorus mainly occur in the MLT sector from midnightside to afternoon, and is generally weak at other MLTs. Near the geomagnetic equator, lower-band chorus is mainly observed during the interval from nightside to dawn and has a MLT extension to dayside at higher magnetic latitudes. Lower- band chorus is mainly confined within 15° of the magnetic latitude around the midnightside （21-- 03 MLT）, while it can propagate to higher latitudes on the dawnside （03-09 MLT）. The global profile of lower-band chorus also manifests a strong L-shell dependence, showing the highest probability of the wave occurrence at L=-4.5 generally and a much broader coverage during geomagnetically active periods. These results concerning the global distribution and occurrence pattern of lower band chorus are important to deepen the current understanding of the wave driven scattering effect on radiation belt electrons via wave-particle interactions and of the quantitative contributions to the dynamic behaviors of radiation belt electrons.