Kinetic analysis of the energy transport of bursty bulk flows in the plasma sheet
Kinetic analysis of the energy transport of bursty bulk flows in the plasma sheet
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DOI：
10.1029/2012ja018351
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发表时间：
2013-01
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通讯作者：
Jinbin Cao;Yuduan Ma;G. Parks;H. Rème;I. Dandouras;Tielong Zhang
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作者：
Jinbin Cao;Yuduan Ma;G. Parks;H. Rème;I. Dandouras;Tielong Zhang
爆发性整体流的能量输运对于理解亚暴能量输运具有重要意义。以往的研究都是利用磁流体力学体参数来计算BBF的能流密度。在本文中，我们使用动力学方法，即，离子速度分布函数，以研究2002年7月30日由星团C1观测到的向地爆发性整体流的能量输运。用动力学方法计算的向地能流密度QKx明显大于用MHD体参数QMHDx计算的向地能流密度。在200-800 km/s流速范围内，QKx/QMHDx的平均值为2.7，表明以前用MHD方法估算的BBF能量输运被大大低估。这种低估是由于离子速度分布偏离理想麦克斯韦分布所致。BBF的能量传输主要由10 keV以上的离子提供，尽管它们的数密度Nf远小于总离子数密度N。QKx/QMHDx的比值基本上与N/Nf的比值成正比。流速v（E）随着能量的增加而增加。比率Nf/N与流速Vx完全成比例。提出了一个双离子组分模型来解释上述结果。BBF能量输送能力的增强对理解亚暴能量输送具有重要意义。对于典型的亚暴，BBF的能量输送占亚暴能量消耗的比例可能会从以前估计的5%增加到34%或更多。
The energy transport of bursty bulk flows (BBFs) is very important to the understanding of substorm energy transport. Previous studies all use the MHD bulk parameters to calculate the energy flux density of BBFs. In this paper, we use the kinetic approach, i.e., ion velocity distribution function, to study the energy transport of an earthward bursty bulk flow observed by Cluster C1 on 30 July 2002. The earthward energy flux density calculated using kinetic approach QKx is obviously larger than that calculated using MHD bulk parameters QMHDx. The mean ratio QKx/QMHDx in the flow velocity range 200–800 km/s is 2.7, implying that the previous energy transport of BBF estimated using MHD approach is much underestimated. The underestimation results from the deviation of ion velocity distribution from ideal Maxwellian distribution. The energy transport of BBF is mainly provided by ions above 10 keV although their number density Nf is much smaller than the total ion number density N. The ratio QKx/QMHDx is basically proportional to the ratio N/Nf. The flow velocity v(E) increases with increasing energy. The ratio Nf/N is perfectly proportional to flow velocity Vx. A double ion component model is proposed to explain the above results. The increase of energy transport capability of BBF is important to understanding substorm energy transport. It is inferred that for a typical substorm, the ratio of the energy transport of BBF to the substorm energy consumption may increase from the previously estimated 5% to 34% or more.