A comparative study of dipolarization fronts at MMS and Cluster.
A comparative study of dipolarization fronts at MMS and Cluster.
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DOI：
10.1002/2016gl069520
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发表时间：
2016-06-28
影响因子：
5.2
通讯作者：
Kepko EL
中科院分区：
文献类型：
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作者：
Schmid D;Nakamura R;Volwerk M;Plaschke F;Narita Y;Baumjohann W;Magnes W;Fischer D;Eichelberger HU;Torbert RB;Russell CT;Strangeway RJ;Leinweber HK;Le G;Bromund KR;Anderson BJ;Slavin JA;Kepko EL
我们利用MMS和Cluster的磁场数据，对径向距离分别低于12r E和20r E的双极化锋（DFs）进行了统计研究。假设DF具有半圆的横截面，并受磁张力推动，我们使用多航天器观测来确定DF的速度。大约四分之三的df向地球传播，大约四分之一向尾部传播。一般来说，MMS处于一个更偶极的磁场区域，并且比Cluster观测到更大的振幅DFs。本研究的主要发现如下：(1)在MMS ~ 57%的DFs移动速度超过150 km/s，而在Cluster只有~ 35%，表明在流制动区域内通量传输速率是可变的。(2) DF速度越大，DF正前方的B - z值越高。我们将其解释为一种类似雪犁的现象，这是由于速度更快的df前面有更高的磁通量堆积造成的。MMS通常位于一个更偶极磁场的区域，与尾部更远的星系团相比，它观察到更大振幅的DF。更大比例的DF移动得更快，更接近地球，这表明在流制动区域的通量传输速率是可变的。DF速度越大，DF正前方的Bz就越大，这表明在速度越快的DF前面有更高的通量堆积
We present a statistical study of dipolarization fronts (DFs), using magnetic field data from MMS and Cluster, at radial distances below 12 R E and 20 R E, 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 B z 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. MMS is generally located in a more dipolar magnetic field region and observes larger‐amplitude DFs than Cluster farther down the tail A larger fraction of DFs move faster closer to Earth, suggesting variable flux transport rates in the flow‐braking region Larger DF velocities correspond to a higher Bz directly ahead of DFs, suggesting a higher flux pileup ahead of DFs with higher velocities