磁层中高纬截止刚度研究以及Fokker-Planck扩散系数矩阵研究

发布时间：2018-02-21 17:08

本文关键词： 地球磁层高能粒子截止刚度 Fokker-Planck方程随机微分方程扩散系数磁暴数值模拟　出处：《中国科学院国家空间科学中心》2016年博士论文　论文类型：学位论文

【摘要】：高能粒子在地球磁层中的传输、加速和损失机制一直是磁层物理研究的重点、热点和难点问题,也是建立空间天气数值预报模式的关键问题。地球磁层结构的复杂性和行星际条件的多变性,使得人们对这个问题的研究变得极其困难。本文通过理论模型、数值模拟和卫星观测相结合的方法对高能粒子在磁层中的传输过程进行系统深入的研究。我们的研究主要包含两部分。第一部分,使用垂直截止刚度的方法研究了高能粒子从中高纬度地区进入磁层空间的相关问题。我们定义了高能粒子进入磁层空间的窗口(CRWs)概念,研究了窗口面积与行星际条件、地磁活动指数的相关关系。宇宙线窗口面积与太阳风参数(例如行星际磁场Bz分量以及太阳风动压Pdyn)相关,其中Bz分量具有最明显的负相关,Pdyn具有正相关性,其他的太阳风参数没有如此强烈的相关性。我们同时模拟了三个不同磁暴期间CRWs的变化情况。研究发现,通常情况下AE指数和CRWs的面积具有正相关,但是Dst指数只有在强磁暴的时候才显示相关性,在中等磁暴和弱磁暴时没有相关性,因此Dst指数不能作为高能粒子进入磁层中高纬度地区的预报指数。研究过程中我们发现高能粒子截止纬度可以使用椭圆进行很好的拟合,我们给定了椭圆的方程表达形式,同时研究了椭圆参数与行星际条件、地磁活动指数的相关关系,给定了椭圆参数的解析表达式。第二部分利用高能粒子传播Fokker-Planck方程,我们对空间高能粒子在磁层传播进行了理论研究,并对方程的数值解法进行深入讨论。我们详细研究了五维扩散系数矩阵的计算方法,并对扩散系数矩阵进行了对比分析。研究发现投掷角扩散系数Dμμ和交叉项扩散系数DYμ基本具有相同的数量级,因此两者在粒子运动过程中具有相同的重要性,尤其是当投掷角余弦是±1时,即粒子的投掷角是0°或者180°时。交叉项扩散系数能引起磁赤道面内粒子的空间位置发生变化,使得粒子可能在磁赤道面内进行振动,获得晨昏向电场的加速。我们的研究对磁层粒子的损失和镜点粒子反弹具有指示意义。
[Abstract]:The mechanism of transmission, acceleration and loss of high-energy particles in the earth's magnetosphere has always been the focal point, hot spot and difficult problem in magnetospheric physics. The complexity of the structure of the magnetosphere and the variability of interplanetary conditions make it extremely difficult to study this problem. Numerical simulation and satellite observation are combined to study the transmission process of high-energy particles in the magnetosphere. Our research mainly consists of two parts. Using the method of vertical cut-off stiffness, we study the problems of high-energy particles entering the magnetosphere space in the middle and high latitudes. We define the concept of window CRWs for high-energy particles entering the magnetosphere space, and study the window area and interplanetary conditions. Correlation of geomagnetic activity index. The cosmic ray window area is correlated with solar wind parameters (such as interplanetary magnetic field Bz component and solar wind dynamic pressure Pdynn), in which Bz component has the most obvious negative correlation and Pdyn has positive correlation. Other solar wind parameters are not so strongly correlated. We also simulated the changes of CRWs during three different magnetic storms. The study found that the AE index and the area of CRWs are generally positively correlated. However, the Dst exponent shows correlation only in strong magnetic storms, but not in moderate and weak magnetic storms. Therefore, the Dst exponent can not be used as the prediction index for high-energy particles entering the magnetosphere at the middle and high latitudes. In the course of the study, we found that the cut-off latitudes of high-energy particles can be well fitted by ellipse, and we have given the expression form of ellipse equation. The correlation between elliptic parameters and interplanetary conditions and geomagnetic activity index is also studied. The analytical expression of elliptic parameters is given. In the second part, the Fokker-Planck equation of high energy particle propagation is used. We studied the propagation of high energy particles in the magnetosphere, and discussed the numerical solution of the equation. We studied the calculation method of the five dimensional diffusion coefficient matrix in detail. The diffusion coefficient matrix is compared and analyzed. It is found that the diffusion coefficient D 渭渭 of the throwing angle and the diffusion coefficient DY 渭 of the cross term have the same order of magnitude, so they have the same importance in the process of particle motion. Especially when the cosine of the throwing angle is 卤1:00, that is, the throwing angle of the particle is 0 掳or 180 掳, the diffusion coefficient of the cross term can cause the change of the space position of the particle in the magnetic equator plane, which may make the particle vibrate in the magnetic equator plane. The acceleration of the electric field is obtained. Our study indicates the loss of magnetospheric particles and the rebound of specular particles.
【学位授予单位】：中国科学院国家空间科学中心
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P353

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