The cusp: a window for particle exchange between the radiation belt and the solar wind
The cusp: a window for particle exchange between the radiation belt and the solar wind
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尖点：辐射带和太阳风之间粒子交换的窗口
DOI：
10.5194/angeo-24-3131-2006
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发表时间：
2006
影响因子：
1.9
通讯作者：
J.
中科院分区：
文献类型：
--
作者：
Xuzhi Zhou;T. Fritz;Q. Zong;Z. Pu;Yongqiang Hao;J.
研究的重点是尖点区域的单粒子动力学。以Tsyganenko 96模型(T96)为例，用磁场iso-B等值线研究了尖点区的拓扑结构，说明了赤道外极小值对粒子捕获的重要性。我们进行了测试粒子模拟来演示弹跳和漂移运动。为了反映高纬磁层中粒子的运动，引入了尖点捕获极限的概念。“尖点捕获极限”的空间分布表明，只有俯仰角接近90°的粒子才能被捕获并在尖点附近漂移。那些俯仰角较小的可能部分被困在iso-B等值线中，然而，它们最终将沿着其中一条磁力线逃逸。在同一漂移轨道内同时存在开放场线和封闭场线，这表明这些粒子可能有两个目的地：沿着开放场线丢失的粒子将连接到磁层顶表面和太阳风，而沿着闭合场线丢失的粒子将进入赤道辐射带。因此，可以认为，尖点区域可以为这两个区域之间的粒子交换提供窗口。一些因素，如偶极子倾角、磁层对流、IMF和Birkland电流系，可能影响尖点的捕获能力，从而影响粒子交换机制。通过尖点磁拓扑分析和试验粒子模拟验证了它们的作用。
The study focuses on a single particle dynamics in the cusp region. The topology of the cusp region in terms of magnetic field iso-B contours has been studied using the Tsyganenko 96 model (T96) as an example, to show the importance of an off-equatorial minimum on particle trapping. We carry out test particle simulations to demonstrate the bounce and drift motion. The "cusp trapping limit" concept is introduced to reflect the particle motion in the high latitude magnetospheric region. The spatial distribution of the "cusp trapping limit" shows that only those particles with near 90° pitch-angles can be trapped and drift around the cusp. Those with smaller pitch angles may be partly trapped in the iso-B contours, however, they will eventually escape along one of the magnetic field lines. There exist both open field lines and closed ones within the same drift orbit, indicating two possible destinations of these particles: those particles being lost along open field lines will be connected to the surface of the magnetopause and the solar wind, while those along closed ones will enter the equatorial radiation belt. Thus, it is believed that the cusp region can provide a window for particle exchange between these two regions. Some of the factors, such as dipole tilt angle, magnetospheric convection, IMF and the Birkeland current system, may influence the cusp's trapping capability and therefore affect the particle exchanging mechanism. Their roles are examined by both the analysis of cusp magnetic topology and test particle simulations.