Low‐frequency electromagnetic waves near and below the proton cyclotron frequency at the AMPTE Ba release: Relevance to comets and Mars
Low‐frequency electromagnetic waves near and below the proton cyclotron frequency at the AMPTE Ba release: Relevance to comets and Mars
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AMPTE Ba 释放时接近和低于质子回旋频率的低频电磁波：与彗星和火星的相关性
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发表时间：
1999
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影响因子：
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通讯作者：
V. Tarasov
中科院分区：
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作者：
K. Sauer;E. Dubinin;M. Dunlop;K. Baumgärtel;V. Tarasov
“非自转质量加载”是太阳风中 AMPTE 钡释放的特征特征，因为与相互作用区域的大小相比，拾取半径较大。在流体图像中，这相当于束流等离子体配置，其中太阳风质子对重质子具有较大的相对速度，可以将其视为未磁化。基于双离子HAl-MHD方程的色散分析给出了两种类型的低频电磁波被激发。 “上”不稳定性发生在哨声/磁声波分支中，其显着特征是最不稳定波的束（航天器）框架中的频率接近质子回旋频率。它的增长率很大程度上取决于电子等离子体β (βe)，它优先决定倾斜传播时的哨声阻尼。因此，生长速率随传播角度的增加受到限制，并且在中间角度（40°≤θ≤70°）处产生“不稳定间隙”。对于 β ≈ 1，仅保留接近平行和横向传播的小范围。对于高射束速度，“较低”的不稳定性由双离子系统的截止频率决定。当 Ba 离子密度降低到低于太阳风密度时，在过渡阶段 AMPTE Ba 释放的磁场数据光谱中可以清楚地看到这两条线。这些结果可能与太空中的其他情况相关：气体产生率低的彗星（q ≤ 1028 s−1）、非磁化行星（金星、火星）和活跃的卫星（火卫一、火卫二）及其气环。
“Nongyrotropic massloading” is a characteristic signature of the AMPTE barium release in the solar wind because of the large pickup radius compared with the size of the interaction region. In the fluid picture this is equivalent to a beam-plasma configuration where the solar wind protons have a large relative velocity to the heavies, which can be considered as unmagnetized. Dispersion analysis on the basis of bi-ion HaIl-MHD equations gives that two types of low-frequency electromagnetic waves are excited. The “upper” instability occurs in the branch of whistler/magnetoacoustic waves with the remarkable feature that the frequency in the beam (spacecraft) frame of the most unstable wave is close to the proton cyclotron frequency. Its growth rate strongly depends on the electron plasma beta (βe) which preferentially determines the whistler damping at oblique propagation. In consequence, the increase of the growth rate with the propagation angle is limited and an “instability gap” results at intermediate angles (40° ≤ θ ≤ 70°). For β ≈ 1, only small ranges near parallel and transverse propagation remain. For a high beam velocity the “lower” instability is determined by the cutoff frequency of the bi-ion system. Both lines were clearly seen in the spectra of magnetic field data of the AMPTE Ba release during the transition phase when the Ba ion density decreases below the solar wind density. These results may be relevant for other situations in space: comets with low gas production rates (q ≤ 1028 s−1), nonmagnetized planets (Venus, Mars)and active moons (Phobos, Deimos) including their gas tori.