本文關(guān)鍵詞： 地球磁層 高能粒子 截止剛度 Fokker-Planck方程 隨機(jī)微分方程 擴(kuò)散系數(shù) 磁暴 數(shù)值模擬　出處：《中國科學(xué)院國家空間科學(xué)中心》2016年博士論文　論文類型：學(xué)位論文

【摘要】：高能粒子在地球磁層中的傳輸、加速和損失機(jī)制一直是磁層物理研究的重點、熱點和難點問題,也是建立空間天氣數(shù)值預(yù)報模式的關(guān)鍵問題。地球磁層結(jié)構(gòu)的復(fù)雜性和行星際條件的多變性,使得人們對這個問題的研究變得極其困難。本文通過理論模型、數(shù)值模擬和衛(wèi)星觀測相結(jié)合的方法對高能粒子在磁層中的傳輸過程進(jìn)行系統(tǒng)深入的研究。我們的研究主要包含兩部分。第一部分,使用垂直截止剛度的方法研究了高能粒子從中高緯度地區(qū)進(jìn)入磁層空間的相關(guān)問題。我們定義了高能粒子進(jìn)入磁層空間的窗口(CRWs)概念,研究了窗口面積與行星際條件、地磁活動指數(shù)的相關(guān)關(guān)系。宇宙線窗口面積與太陽風(fēng)參數(shù)(例如行星際磁場Bz分量以及太陽風(fēng)動壓Pdyn)相關(guān),其中Bz分量具有最明顯的負(fù)相關(guān),Pdyn具有正相關(guān)性,其他的太陽風(fēng)參數(shù)沒有如此強(qiáng)烈的相關(guān)性。我們同時模擬了三個不同磁暴期間CRWs的變化情況。研究發(fā)現(xiàn),通常情況下AE指數(shù)和CRWs的面積具有正相關(guān),但是Dst指數(shù)只有在強(qiáng)磁暴的時候才顯示相關(guān)性,在中等磁暴和弱磁暴時沒有相關(guān)性,因此Dst指數(shù)不能作為高能粒子進(jìn)入磁層中高緯度地區(qū)的預(yù)報指數(shù)。研究過程中我們發(fā)現(xiàn)高能粒子截止緯度可以使用橢圓進(jìn)行很好的擬合,我們給定了橢圓的方程表達(dá)形式,同時研究了橢圓參數(shù)與行星際條件、地磁活動指數(shù)的相關(guān)關(guān)系,給定了橢圓參數(shù)的解析表達(dá)式。第二部分利用高能粒子傳播Fokker-Planck方程,我們對空間高能粒子在磁層傳播進(jìn)行了理論研究,并對方程的數(shù)值解法進(jìn)行深入討論。我們詳細(xì)研究了五維擴(kuò)散系數(shù)矩陣的計算方法,并對擴(kuò)散系數(shù)矩陣進(jìn)行了對比分析。研究發(fā)現(xiàn)投擲角擴(kuò)散系數(shù)Dμμ和交叉項擴(kuò)散系數(shù)DYμ基本具有相同的數(shù)量級,因此兩者在粒子運動過程中具有相同的重要性,尤其是當(dāng)投擲角余弦是±1時,即粒子的投擲角是0°或者180°時。交叉項擴(kuò)散系數(shù)能引起磁赤道面內(nèi)粒子的空間位置發(fā)生變化,使得粒子可能在磁赤道面內(nèi)進(jìn)行振動,獲得晨昏向電場的加速。我們的研究對磁層粒子的損失和鏡點粒子反彈具有指示意義。
[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 鹵1:00, that is, the throwing angle of the particle is 0 擄or 180 擄, 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.
【學(xué)位授予單位】：中國科學(xué)院國家空間科學(xué)中心
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：P353

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本文編號：1522406