Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations
Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations
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DOI：
10.5194/angeo-27-2259-2009
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发表时间：
2009-06
影响因子：
1.9
通讯作者：
O. Contel;A. Roux;C. Jacquey;P. Robert;M. Berthomier;T. Chust;B. Grison;V. Angelopoulos;D. Si
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作者：
O. Contel;A. Roux;C. Jacquey;P. Robert;M. Berthomier;T. Chust;B. Grison;V. Angelopoulos;D. Si
抽象的。我们报告了 THEMIS 任务的近地卫星在局部两极化之前、期间和之后检测到的准平行哨声发射。这些发射与电子温度各向异性 α=T⊥e/T||e>1 相关，与惠斯勒模式各向异性不稳定性的线性理论一致。当观察到哨声模式发射时，测量到的电子各向异性与 β||e（电子平行压力与磁压力之比）成反比，正如 Gary 和 Wang (1996) 所预测的那样。窄带哨声发射对应于偶极化之前存在的小α，而宽带发射对应于偶极期间和之后观察到的大α。哨声模式的能量离开电流片并沿着背景磁场向地球传播。基于刘维尔定理的简单与时间无关的描述表明，电子温度各向异性随着沿磁场距赤道的距离的增加而减小。一旦考虑到 α 的这种变化，线性理论就可以预测口哨模式的赤道原点。线性理论也与观测到的波发射带宽一致。然而，与观测结果完全一致所需的各向异性比测量值稍大。尽管差异仍然在仪器误差范围内，但这可能是由于被忽略的时间相关效应造成的。讨论了啸声波在亚暴过程中的可能作用。
Abstract. We report on quasi-parallel whistler emissions detected by the near-earth satellites of the THEMIS mission before, during, and after local dipolarization. These emissions are associated with an electron temperature anisotropy α=T⊥e/T||e>1 consistent with the linear theory of whistler mode anisotropy instability. When the whistler mode emissions are observed the measured electron anisotropy varies inversely with β||e (the ratio of the electron parallel pressure to the magnetic pressure) as predicted by Gary and Wang (1996). Narrow band whistler emissions correspond to the small α existing before dipolarization whereas the broad band emissions correspond to large α observed during and after dipolarization. The energy in the whistler mode is leaving the current sheet and is propagating along the background magnetic field, towards the Earth. A simple time-independent description based on the Liouville's theorem indicates that the electron temperature anisotropy decreases with the distance along the magnetic field from the equator. Once this variation of α is taken into account, the linear theory predicts an equatorial origin for the whistler mode. The linear theory is also consistent with the observed bandwidth of wave emissions. Yet, the anisotropy required to be fully consistent with the observations is somewhat larger than the measured one. Although the discrepancy remains within the instrumental error bars, this could be due to time-dependent effects which have been neglected. The possible role of the whistler waves in the substorm process is discussed.