行星际-赤道电场穿透效率的数值模拟研究

A modeling study of interplanetary-equatorial electric field penetration efficiency

电场穿透作为强烈地磁活动期间太阳风-磁层-电离层电动力学耦合的重要形式,近年来一直是空间物理学最为活跃的课题之一.在过去的近40年里人们一直关注于观测证据的寻找以及物理过程的模拟,"电场穿透效率"这一重要定量化指标直到最近几年才得到重视.本文定义赤道电场增量与对应的行星际电场增量的比值为穿透效率,通过数值模拟的方法对穿透效率的地方时变化以及与中性风发电机的关系做了实验性讨论,在一定简化条件下结果表明:(1)不考虑跨极盖电势饱和的情况下,赤道电场增量与行星际电场增量呈线性关系,且中性风发电机并不影响电场穿透效率;(2)恒定重联线长度L的限定下,穿透效率具有明显地方时依赖性.例如对于L=2.6RE,在9LT至23LT之间,穿透效率维持在10%左右;0LT至7LT之间,穿透效率迅速从2%上升至30%后又迅速回落到原始水平,形成尖峰.这些结果基本符合观测特征.

As an important way of solar wind-magnetosphere-ionosphere coupling during strong geomagnetic activity period, electric field penetration has been an active topic in space physics for many years. In the past four decades, many researchers were interested in the observational evidence and theoretic modeling to search for the physical mechanism, however, the ＂electric field penetration efficiency＂, which is supposed to be an important quantitative index, has received less attention. Defining the penetration efficiency as the ratio of equatorial electric field increment to the corresponding interplanetary electric field increment, this paper aims to discuss the local time dependence of electric field penetration efficiency and its relation to neutral wind. Our result of numerical modeling suggests that： （1） Without considering transpolar potential saturation, equatorial electric field increment linearly responds to IEF increment, and neutral wind does not affect the penetration efficiency; （2） Assuming constant magnetic reconnection length L=2. 6 RE,the local time dependence of penetration efficiency can be described as follows： it is about 10% between 9 and 23LT, however, increases rapidly from 2% up to 30% and decreases quickly to 2% between 0 and 7LT. All above characteristics are basically consistent with observations.