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首页> 外文期刊>Space Science Reviews >THEORETICAL APPROACHES TO THE DESCRIPTION OF MAGNETIC MERGING - THE NEED FOR FINITE BETA(E), ANISOTROPIC, AMBIPOLAR HALL MHD
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THEORETICAL APPROACHES TO THE DESCRIPTION OF MAGNETIC MERGING - THE NEED FOR FINITE BETA(E), ANISOTROPIC, AMBIPOLAR HALL MHD

机译：磁融合描述的理论方法-有限β，各向异性，两极霍尔MHD的需求

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Theoretical models of magnetic reconnection are reviewed with a critical view of their suitability for astrophysical plasmas, with a focus on those sampled plasmas near the magnetopause. Frequently the approximations are more those of convenience than physically justified. It is concluded that magnetic reconnection cannot be qualitatively or quantitatively addressed with any one fluid MHD picture unless the Hall, ambipolar and inertial emfs are included in the Generalized Ohm's Law. The observed size of electron pressure anisotropies ensures that the thawing of magnetic flux is almost always determined by the often neglected ambipolar term of the Generalized Ohm's Law. Thus resistive MHD or even resistive Hall MHD cannot possibly give a correct structural picture of the reconnection current carrying layer at the magnetopause. In the magnetotail the ion inertial ''resistivity'' is much larger than coulomb resistivity with a similar structural form as the coulomb emf. However, until recently the ambipolar contributions there have not been considered. This change in viewpoint of the controlling factors for thawing of magnetic Aux parallels the recent evolution of understanding of collisionless shocks, where initially stochastic wave-resistivities were thought to substitute for the coulomb dissipation of high density shock waves. Now these shocks are known to be controlled by coherent agents that can modify emf's such as the ambipolar electric field, the Hall contributions of the gyrating ions, and the electric electron drift in the shock layer to support the current without thawing flux and without any requirement of ohmic dissipation per se. The observational tests that reconnection is a viable process for plasma entry in the magnetosphere are briefly reviewed. Sites where these conservation laws are said to be approximately fulfilled are discussed with an eye toward systematic experimental issues of these tests. That magnetic shear poorly indexes ''good'' Walen testing layers may be an indication that the resistive dissipation is either not uniformly important across the data set or resistive emf's are not the appropriate agent for the thawing of flux. The ambipolar scale length clearly exceeds the resistive or electron skin depth regime with layers that pass the ''good'' Walen test layers which have beta < 5; this may indicate the importance of the ambipolar violations to the frozen field description. [References: 69]
机译：回顾了磁重合的理论模型，并对它们对天体等离子体的适用性提出了批判性观点，并着重介绍了磁层顶附近的那些采样等离子体。通常，逼近比起物理上的合理性，更接近于便利性。结论是，除非霍尔姆，双极性和惯性电动势包含在广义欧姆定律中，否则用任何一张流体MHD图都无法定性或定量地解决磁重连接问题。观察到的电子压力各向异性的大小确保了磁通量的解冻几乎总是由广义欧姆定律中经常被忽略的双极性项决定的。因此，电阻性MHD或什至电阻性霍尔MHD都无法给出磁停顶处重新连接载流层的正确结构图。在磁尾中，离子惯性的“电阻率”比具有与库仑电动势相似的结构形式的库仑电阻率大得多。但是，直到最近，还没有考虑过歧义的贡献。磁辅助解冻的控制因素观点上的这种变化与无碰撞冲击的理解的最新发展相平行，在无碰撞冲击中，最初的随机波电阻率被认为可以代替高密度冲击波的库仑耗散。现在，已知这些冲击是由相干剂控制的，这些相干剂可以改变电动势，例如双极性电场，旋转离子的霍尔贡献以及电子在冲击层中的漂移，以在不解冻通量且不需要任何条件的情况下支撑电流本身的欧姆耗散。简要回顾了重新连接是磁层中等离子体进入的可行过程的观察性测试。讨论了这些守恒定律已基本实现的站点，着眼于这些测试的系统性实验问题。磁切变指数不佳的“良好” Walen测试层可能表明电阻耗散在整个数据集中不是很重要，或者电阻电动势不是解决通量解冻的合适方法。双极尺度长度明显超过了电阻或电子趋肤深度范围，其层通过了“良好的” Walen测试层，其beta <5;这可能表明双极违反对冻结字段描述的重要性。 [参考：69]

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