The effects of a conducting E layer on classical F region cross‐field plasma diffusion
The effects of a conducting E layer on classical F region cross‐field plasma diffusion
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导电E层对经典F区交叉场等离子体扩散的影响
DOI：
10.1029/ja087ia06p04461
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发表时间：
1982
影响因子：
--
通讯作者：
M. Kelley
中科院分区：
文献类型：
--
作者：
J. Vickrey;M. Kelley
当磁力线穿过下面的高导电性E区时，F区电离层中的跨场等离子体扩散速率显著增加。这缩短了极地电离层中小尺度F区电子密度不规则性的寿命，在极地电离层中，高导电性E区的存在是常见的。建立了一个简单的模型来描述导电E层对经典F区等离子体扩散的影响。在没有E区的情况下，离子和电子扩散速率的差异导致电荷分离，从而产生抑制离子扩散的静电场。然而，当高导电性的磁力线被绑在导电的E区时，电子可以沿着B流动以降低双极扩散电场，并且离子可以以接近其自身(更高)扩散速度的速率垂直于B前进。结果表明，增强的总扩散速率强烈地依赖于F层的高度和E/F区Pedersen电导的比值。虽然增强的经典扩散速度在它们的产生源被移除后加速了不规则的消除，但它不是一个足够强大的阻尼机制来防止不稳定在极地电离层常规运行。然而，E区可能在决定被看好的不规则性的尺度大小方面起着重要作用。对于较低的E区电子密度和较小的尺度尺寸，E区‘图像’可能很重要，在这种情况下，扩散速率会降低。然而，如果E区的电导率很高，图像的存在只会使F区的跨场等离子体扩散速率从离子速率降低约25%。我们假设高纬等离子体密度不规则性的谱在大尺度(λ≳10公里)上受结构软电子沉淀和经典扩散的控制。大尺度结构边缘的等离子体不稳定性产生了较小尺度的波。广义不稳定(包括目前的对流过程)在几何形状合适或场向电流显著的区域起到了加强中尺度(100m≤λ≤10公里)波的作用。普遍的漂移波将能量从中尺度传递到较小的结构，但在大尺度上无效。将本文描述的经典扩散过程(结合不规则产生和对流的模型)应用于解释伴随论文中的大尺度高纬度不规则的形态的问题(Kelley等，本期)。对上述不稳定引起的反常扩散也作了更详细的描述。
The rate of cross-field plasma diffusion in the F region ionosphere is significantly increased when the magnetic field lines thread a highly conducting E region below. This reduces the lifetime of small-scale F region electron density irregularities in the polar ionosphere where the presence of a highly conducting E region is commonplace. A simple model is developed to describe the effects of a conducting E layer on classical F region plasma diffusion. In the absence of an E region, the difference in ion and electron diffusion rates leads to a charge separation and, hence, to an electrostatic field that retards ion diffusion. When the highly conducting magnetic field lines are tied to a conducting E region, however, electrons can flow along B to reduce the ambipolar diffusion electric field, and ions can proceed perpendicular to B at a rate approaching their own (higher) diffusion velocity. It is shown that the enhanced total diffusion rate that results depends strongly on the height of the F layer and on the ratio of the E to F region Pedersen conductivities. Although the enhanced classical diffusion rate hastens the removal of irregularities once their production source is removed, it is not a strong enough damping mechanism to prevent instabilities from operating routinely in the polar ionosphere. However, the E region probably plays an important role in determining the scale size of the irregularities that are favored. E region ‘images’ may be important for low E region electron densities and small scale sizes, in which case the diffusion rate is lowered. However, if the E region conductivity is high, the presence of images only reduces the F region cross-field plasma diffusion rate by about 25% from the ion rate. We hypothesize that the spectrum of high-latitude plasma density irregularities is controlled at large scales (λ ≳ 10 km) by structured soft electron precipitation and classical diffusion. Smaller scale waves are produced by plasma instabilities operating on the edges of the large scale structures. The generalized instability (including the current convective process) acts to strengthen waves in the intermediate scale size (100 m ≤ λ ≤ 10 km) in regions where the geometry is appropriate or where field-aligned currents are significant. Universal drift waves transfer energy from the intermediate scale to smaller structures but are ineffectual at large scales. The classical diffusion process described herein is applied (in conjunction with a model of irregularity production and convection) to the problem of explaining the morphology of the large scale high-latitude irregularities in a companion paper (Kelley et al., this issue). The anomalous diffusion due to the instabilities mentioned above is also described in more detail.