基于NOAA卫星数据的辐射带质子投掷角分布研究

利用NOAA-12卫星数据对空间环境平静时期太阳同步轨道处辐射带质子投掷角分布进行了研究. 根据投掷角分布的经验公式，计算出90°投掷角的质子方向强度和各向异性指数n. 质子投掷角分布按n的取值范围可分为三类，即90°峰值分布、平顶分布和蝴蝶形分布. 观测证实，对于辐射带质子，三种分布类型均存在并且具有明显的空间区域特征. 在内辐射带边缘地区90°峰值分布占主要优势；在外辐射带高L值区域，90°峰值分布明显减少，平顶分布和蝴蝶形分布逐渐增多. 针对90°峰值分布，研究了质子强度各向异性的区域分布特征，对于内辐射带区域，n值随L值的增大而增大，对于外辐射带，n值表现为逐渐下降的趋势. 为了研究质子投掷角分布对磁地方时的依赖关系，分析了能量为250～800keV的质子在两个不同磁地方时范围的投掷角分布规律. 结果显示，在内辐射带，质子强度的投掷角分布相对稳定，随磁地方时的变化并不显著；而在外辐射带的高L值区域，质子强度的投掷角分布随磁地方时变化明显，与磁地方时之间有明显的依赖关系. 

Pitch Angle Distribution Research of Radiation Belt Protons Based on the NOAA Data

Using the NOAA-12 satellite data, a study on the Pitch Angle Distributions (PADs) of energetic protons is performed during the quiet period of space environment in the Sun-synchronous orbit. The 90° pitch angled proton flux and the anisotropy index n are calculated based on the empirical formula. According to the n values, it's found that the distributions can be classified into three categories: 90° peaked, flattop, and butterfly. For the radiation belt protons, the three types are all existed and have a significant spatial character. The 90° peaked distributions dominate at the edge of inner radiation belt; while at the higher L values region of outer radiation belt, the 90° peaked distributions decrease obviously and the flattop distribution and butterfly distribution gradually increase with the increase of L values. For the 90° peaked distributions, relationship between the anisotropy exponent n and the L values is studied. For inner radiation belt, the n values increase rapidly with the L values increasing; for outer radiation belt, the n values decrease gradually with the L values increasing. The distributions of the radiation belt protons are also studied in two different Magnetic Local Time (MLT) regions for the 250～800keV protons. The results show that the PADs are very similar at the inner radiation belt, but have obvious differences at the higher L values region of outer radiation belt. It indicates that the PADs of radiation belt protons have little dependency on the MLT at the inner radiation belt, while have more dependency on the MLT at the higher L values region of outer radiation belt.