Schmid D, Nakamura R, Volwerk M, Plaschke F, Narita Y, Baumjohann W, Magnes W, Fischer D, Eichelberger H U, Torbert R B, Russell C T, Strangeway R J, Leinweber H K, Le G, Bromund K R, Anderson B J, Slavin J A, Kepko E L
Space Research Institute Austrian Academy of Sciences Graz Austria; NAWI Graz University of Graz Graz Austria.
Space Research Institute Austrian Academy of Sciences Graz Austria.
Geophys Res Lett. 2016 Jun 28;43(12):6012-6019. doi: 10.1002/2016GL069520. Epub 2016 Jun 25.
We present a statistical study of dipolarization fronts (DFs), using magnetic field data from MMS and Cluster, at radial distances below 12 and 20 , respectively. Assuming that the DFs have a semicircular cross section and are propelled by the magnetic tension force, we used multispacecraft observations to determine the DF velocities. About three quarters of the DFs propagate earthward and about one quarter tailward. Generally, MMS is in a more dipolar magnetic field region and observes larger-amplitude DFs than Cluster. The major findings obtained in this study are as follows: (1) At MMS ∼57 % of the DFs move faster than 150 km/s, while at Cluster only ∼35 %, indicating a variable flux transport rate inside the flow-braking region. (2) Larger DF velocities correspond to higher values directly ahead of the DFs. We interpret this as a snow plow-like phenomenon, resulting from a higher magnetic flux pileup ahead of DFs with higher velocities.
我们分别利用来自磁层多尺度任务（MMS）和星簇计划（Cluster）在径向距离低于12个地球半径和20个地球半径处的磁场数据，对双极化前沿（DFs）进行了统计研究。假设双极化前沿具有半圆形横截面且由磁张力推动，我们利用多航天器观测来确定双极化前沿的速度。大约四分之三的双极化前沿向地球方向传播，约四分之一向尾部传播。一般来说，磁层多尺度任务处于磁场更具偶极性的区域，并且比星簇计划观测到的双极化前沿幅度更大。本研究获得的主要发现如下：（1）在磁层多尺度任务处，约57%的双极化前沿移动速度超过150千米/秒，而在星簇计划处只有约35%，这表明在流制动区域内通量传输速率是可变的。（2）双极化前沿速度越大，其正前方的β值越高。我们将此解释为一种类似扫雪机的现象，这是由速度较高的双极化前沿前方更高的磁通量堆积导致的。
