极光电集流活动的变化特征与形成机制研究

Auroral electrojet are the horizontal currents that flow in the D and E regions of the auroral ionosphere, and they are controlled mainly by the north-south component of the electric field and the Hall conductance over the region. Generally, the maximum current density and total current as well as the latitude of the maximum current density can be determined from magnetic measurements. In past years, little progress was made in understanding the auroral electrojet activity, because of the limits of the magnetic measurements, such as the sparseness of the magnetometer stations. Now observations from the IMAGE magnetometer chain and the SuperMAG magnetometer chain offer us opportunities to gain new physical insight into the processes governing the eastward and westward auroral electrojets. In this proposal, we plan to investigate the the characteristics of auroral electrojets in different MLT regions and their formation mechanisms using the IMAGE and SuperMAG network magnetic measurements, and then embody our knowledge into new physics-based models. The scientific results from the project will help to develop empirical models for auroral electrojet activity prediction purposes, and will significantly advance knowledge of solar wind- magnetosphere-ionosphere (SMI) coupling.

极光电集流是极光纬度上最显著的全球性电流体系，主要受电导率和南北向电场控制。通常，极光电集流的强度和分布可以用地面观测的磁场值来估算。过去受制于地磁台链的局限，比如台站覆盖范围太小、台站分布不均匀等，极光电集流活动特征与形成机制的研究进展甚微。近几年地磁台链的迅速发展，尤其是IMAGE地磁台链和SuperMAG地磁台链，为进一步挖掘与认识极光电集流变化特征提供了新途径。本项目拟利用这些地磁台链的数据资料，研究极光电集流活动在不同地方时区的变化特征及其背后的机制，建立反映这些特征与机制的物理模型，为构建有效的极光电集流预报模型提供物理基础。研究成果将有助于我们进一步认识太阳风-磁层-电离层的耦合过程。

IMAGE和SuperMAG地磁台链的迅速发展为进一步认识与挖掘极光电集流活动提供了新途径。本项目利用这些地磁台链数据，研究了极光电集流在不同地方时区的变化特征与形成机制，以及极光电集流脉冲增强激发的热层重力波活动，取得了一些研究成果：（1）首次发现西向电集流在子夜扇区存在显著的年变化特征，并将它归因于粒子沉降和对流电场的调制作用；（2）揭示了极光电集流强度和中心纬度位置随磁地方时和季节的变化特征；（3）探测到相互作用的日冕物质抛射与太阳风阿尔芬波驱动极光电集流脉冲增强进而激发的多步大尺度热层重力波；（4）在大尺度热层重力波的传播特性方面，发现了迄今为止在热层传播最远的大尺度重力波；找到了两列大尺度重力波相干的观测证据。这些成果将有助于我们进一步认识太阳风-磁层-电离层的耦合过程，对低轨卫星的轨道控制与姿态保持有重要意义。