Statistical analysis of pitch angle distribution of radiation belt energetic electrons near the geostationary orbit: CRRES observations
Statistical analysis of pitch angle distribution of radiation belt energetic electrons near the geostationary orbit: CRRES observations
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DOI：
10.1029/2010ja016052
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发表时间：
2011
影响因子：
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通讯作者：
X. Gu;Zhengyu Zhao;B. Ni;Y. Shprits;Chen Zhou
中科院分区：
文献类型：
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作者：
X. Gu;Zhengyu Zhao;B. Ni;Y. Shprits;Chen Zhou
[1]本文根据释放与辐射效应综合卫星（CRRES）上的中电子A（MEA）仪器的俯仰角分辨通量观测资料，对径向距离为6 RE和6.6RE的高能辐射带电子俯仰角分布（PAD）进行了统计分析。Vampola（1998）和Gannon等人（2007）以前的研究使用CRRES MEA数据来研究特定能量下电子PAD的一般变化，在这项研究中，我们对电子PAD进行了详细的统计分析，包括对电子动能的依赖性，磁本地时间（MLT）和地磁活动水平。通过用局部俯仰角正弦的幂律函数拟合实测PAD，将与辐射带电子PAD类别相关的幂律指数n详细量化为电子动能、MLT间隔和地磁指数Kp的函数。统计平均n值相对于MLT变化很大，从0000-0400 MLT内的n ≥ 0到1200-1600 MLT内的n ≥ 1.5，这是因为波散射与MLT的关系以及与漂移壳分裂和磁层顶阴影相关的影响。漂移壳层分裂和磁层顶遮蔽导致经常观测到的负n值。在几百keV的较低能量的俯仰角分布是更平坦的比在兆电子伏的能量，这是一致的更快的俯仰角散射在低能量的合唱波。这些辐射带电子PAD的定量结果与Vampola（1998年）和Gannon等人（2007年）先前的研究一致，为地球静止轨道附近高能辐射带电子的全球动态提供了进一步的见解，也有助于推断电子相空间密度和使用全向电子通量测量同化其径向轮廓。
[1] A statistical analysis of energetic radiation belt electron pitch angle distributions (PADs) at the radial distances of 6 RE and 6.6 RE is performed on the basis of the pitch angle resolved flux observations from the Medium Electrons A (MEA) instrument onboard the Combined Release and Radiation Effects Satellite (CRRES). While previous studies of Vampola (1998) and Gannon et al. (2007) have used CRRES MEA data to investigate the general variations in electron PAD at particular energies, in this study we present a detailed statistical analysis of electron PADs including the dependence on electron kinetic energy, magnetic local time (MLT), and the level of geomagnetic activity. By fitting the measured PADs with a power law function of sine of local pitch angle, the power law index n that relates to the category of radiation belt electron PAD is quantified in detail as a function of electron kinetic energy, MLT interval, and geomagnetic index Kp. Statistical averaged n values vary considerably with respect to MLT, ranging from n ∼ 0 within 0000–0400 MLT to n ∼ 1.5 within 1200–1600 MLT, because of the MLT dependence of wave scattering and the effects associated with drift shell splitting and magnetopause shadowing. Drift shell splitting and magnetopause shadowing result in often observed negative values of n. At lower energies of a few hundred keV the pitch angle distributions are more flat than at MeV energies, which is consistent with faster pitch angle scattering at low energies by chorus waves. These quantitative results of radiation belt electron PAD, consistent with the previous studies by Vampola (1998) and Gannon et al. (2007), provide further insight into the global dynamics of energetic radiation belt electrons near the geostationary orbit and also are useful for inferring electron phase space densities and assimilating their radial profiles using omnidirectional electron flux measurements.