• ISSN 2097-1893
  • CN 10-1855/P

地球内磁层低纬大尺度电场研究进展

State studies of the large-scale electric fields in the low-latitude region of Earth's inner magnetosphere

  • 摘要: 地球内磁层的大尺度电场由太阳风与地球磁场的相互作用产生. 在高纬区域,平行电场起着更为重要的作用,而在低纬地区,电场则主要表现为共转电场、对流电场和脉冲电场. 本文着重讨论低纬区域大尺度电场的特征及其在内磁层中的作用,这些电场共同作用于内磁层中的多种动力学过程. 共转电场和对流电场驱动的电场漂移分别引起地球磁层等离子体的共转运动和对流运动,从而决定了等离子体层的形态及其动态演化;而脉冲电场能加速内磁层的带电粒子,并且导致高能粒子的向内注入. 近年来,基于卫星观测的研究表明,大尺度电场的分布受到地磁活动和太阳风条件的显著影响. 对流电场整体呈晨昏向,但其在内磁层中的空间分布并不均匀. 在距离地球约5个地球半径(RE)范围内,对流电场受到明显屏蔽,其屏蔽边界会随着Kp指数的增加逐渐向地球方向移动. 此外,亚极光区极化流在距地球约4 RE的区域引起了强径向电场,显著影响了磁地方时黄昏到午夜区域对流电场的分布. 磁暴主相期间以及行星际磁场南转后,对流电场会显著增强,但不同区域的电场增强幅度或响应时间存在差异. 共转电场基于等离子体层24小时的共转周期进行计算. 然而,观测研究表明,等离子体层存在共转滞后现象,这意味着共转电场强度可能被高估. 在行星际激波事件中,增强的动压会压缩磁层并激发脉冲电场. 脉冲电场在内磁层中的传播速度与快磁声波及行星际激波的传播速度密切相关,其中快磁声波的速度决定了脉冲电场的初始响应时间,而行星际激波的速度则与脉冲电场的峰值到达时间相对应. 本文回顾了近年来对流电场、共转电场和脉冲电场的研究进展,并展望了内磁层大尺度电场研究中亟待解决的科学问题.

     

    Abstract: The large-scale electric fields in Earth's inner magnetosphere are generated by the interaction between the solar wind and Earth's magnetic field. In high-latitude regions, parallel electric fields are dominant, while in low-latitude regions, the convection, corotation, and impulsive electric fields play a crucial role in the dynamics of the inner magnetosphere. This review examines the characteristics of large-scale electric fields in low-latitude regions and their effects on magnetospheric processes. The convection and corotation electric field, driving the plasma drift, determine the topology of the plasmasphere. The impulsive electric field, accelerating charged particles quickly, leads to the inward injection of energetic particles. Convection electric fields, driven by dayside plasma flows from the magnetotail, exhibit a non-uniform spatial distribution. Recent satellite observations reveal that their distribution is influenced by geomagnetic and solar activity. Shielding effects limit the dawn-to-dusk electric field within approximately 5 Earth radii (RE) during low geomagnetic activity (e.g., Kp=1), with the shielding boundary shifting inward as geomagnetic activity intensifies. Subauroral polarization streams are associated with intense radial electric fields at approximately 4 RE, significantly affecting the distribution of the convection electric field from dusk to midnight. Recent studies also show that the convection electric field distribution varies during different phases of magnetic storms, with electric fields penetrating deeper into the inner magnetosphere during the main phase, and shielding effects dominating during the recovery phase. During the magnetic storm's main phase, or after a southward turning of the interplanetary magnetic field, the dawn-to-dusk electric field is enhanced, with the amplitude and response time varying across different regions. Corotation electric fields arise from the plasma's rotational motion with Earth. However, observations indicate that the plasmasphere experiences a corotation lag, suggesting that corotation electric fields may be overestimated when based on the 24-hour corotation period of the plasmasphere. Recent studies have shown that this corotation lag may be linked to energy and momentum transfer processes in the ionosphere or thermosphere. The ionospheric dynamo mechanism, driving neutral winds toward the equator, plays a critical role in this corotation lag. Impulsive electric fields are transient phenomena triggered by interplanetary shocks or substorms. They play a crucial role in accelerating charged particles, leading to inward injections of energetic particles. SWMF simulations have provided insights into the spatiotemporal evolution of impulsive electric fields during interplanetary shock events. The propagation speed of impulsive electric fields is closely related to the propagation speeds of fast-mode waves and interplanetary shocks, which determine their initial response and peak arrival times. Despite significant advancements, challenges persist in accurately modeling shielding and penetration electric fields, understanding their global and synchronous response to interplanetary magnetic field variations, and distinguishing between different types of electric fields. Addressing these challenges is essential for advancing our understanding of the magnetosphere's dynamics and its interaction with the solar wind. This review summarizes recent advances in the study of convection, corotation, and impulsive electric fields, highlighting unresolved scientific questions and the need for further investigations in the inner magnetosphere.

     

/

返回文章
返回