地球电子外辐射带的数据同化建模与分析

地球电子外辐射带对太阳与地磁活动呈现高度动态变化的响应,了解外辐射带的全球动态变化过程对于近地空间粒子辐射环境的理解认知和预测预报具有重要意义.基于卡尔曼滤波数据同化方法,本文利用范阿伦A星、B星和GOES-13和GOES-15四颗卫星的辐射带电子观测数据,分别利用三种不同维度的辐射带物理模型,将观测结果与数值结果有机融合,对2013年3月地球外辐射带电子通量的径向分布与变化进行数据同化分析.结果表明,考虑了磁层波动与辐射带电子共振作用引起的径向扩散、投掷角扩散以及能量扩散过程的三维同化模型可有效、合理地重现外辐射带电子通量的径向分布.本文进一步利用该三维同化模型对2013年一整年外辐射带电子的相空间密度分布进行重构与分析,得到了不同绝热不变量和不同地磁活动条件下电子辐射带的时空演化过程,从而为深入理解外辐射带电子的变化过程和动力学机制提供了强有力信息.通过分析同化过程中的新息矢量以及度量同化过程中观测数据在多大程度上修改了物理模型结果,还有助于定量分析现有辐射带物理模型中的源项和损失项的相对贡献以及可能忽略的物理机制或过程.

Multi-dimensional data assimilation and analyses of Earth's outer electron radiation belt

Responses of Earth′s outer electron radiation belt to solar and geomagnetic activities are highly dynamic.Exploration of the dynamic variability of the outer radiation belt is of significance to comprehending,nowcasting and forecasting the complex particle radiation environment in geospace.Using the Kalman filter method,we combine the radiation belt electron observations from four satellites,i.e.,Van Allen Probes A and B,GOES-13 and GOES-15,with three physical models of the outer electron radiation belt with different dimensions to assimilate the radial distributions and variations of outer radiation belt electron fluxes in March 2013.Detailed analyses of the assimilative results demonstrate that the three-dimensional(3-D)assimilation model that includes the effects of radial diffusion,pitch-angle diffusion and energy diffusion can reproduce effectively and reasonably the radial distributions and temporal changes of outer radiation belt electron fluxes.We further adopt this 3-D outer radiation belt data assimilation model to reconstruct and evaluate the dynamic variations of outer radiation belt electron phase space densities(PSD)for different values of the adiabatic invariants under different geomagnetic conditions over the entire year of 2013.The assimilative spatio-temporal evolution of outer radiation belt electron PSD provides robust information of the long-term radial profiles of outer radiation belt electrons to understand the underlying physical processes and dynamic mechanisms.In terms of calculations of the innovation vector and evaluations of how satellite observations can alter the simulation results of the physical radiation belt model,we can quantitatively evaluate the relative contributions of the source,acceleration and loss terms considered in the physical model and explore as well the physical processes/mechanisms that may be missing in it.