Observational evidence for new instabilities in the midlatitude E and F region
Observational evidence for new instabilities in the midlatitude E and F region
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DOI：
10.5194/angeo-34-927-2016
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发表时间：
2016-11-03
影响因子：
1.9
通讯作者：
Sulzer, Michael
中科院分区：
文献类型：
--
作者：
Hysell, David L.;Larsen, Miguel;Sulzer, Michael
本文介绍了阿雷西博天文台在中等扰动条件下对E区和F区电离层进行的雷达观测。观测结果表明，存在斑片状的零星E（E-S）层，中等规模的旅行电离层扰动（MSTIDS），和耗尽羽流与扩展F条件。新的分析技术被应用到数据集来推断矢量等离子体漂移在F区域以及矢量中性风和温度廓线在E区域。在这两个地区的不稳定机制进行了评估。中层低热层（MLT）区域被发现，以满足中性动力不稳定的条件，在附近的斑片状的Es层，即使风切变是相对温和的。在MLT温度分布的逆温显着贡献的不稳定性在附近的一个补丁层。特别令人感兴趣的是，由于温度随高度迅速上升，在低热层区域（通常与高度稳定的条件有关）中性对流不稳定所需条件的证据。一个局部的F-区域等离子体密度增强与磁场的突然上升，创造必要的条件对流等离子体不稳定性，导致耗尽羽流和传播F。与Perkins（1973）描述的不稳定性相比，不稳定性的增长时间很短。这种不稳定性并没有提供一个简单的解析解，但在数值模拟中明显存在。不稳定模式以前没有被描述过，但似乎比以前提出的各种机制更可行，作为中纬度扩展F的发生的解释。
Radar observations of the E- and F-region ionosphere from the Arecibo Observatory made during moderately disturbed conditions are presented. The observations indicate the presence of patchy sporadic E (E-s) layers, medium-scale traveling ionospheric disturbances (MSTIDs), and depletion plumes associated with spread F conditions. New analysis techniques are applied to the dataset to infer the vector plasma drifts in the F region as well as vector neutral wind and temperature profiles in the E region. Instability mechanisms in both regions are evaluated. The mesosphere-lower-thermosphere (MLT) region is found to meet the conditions for neutral dynamic instability in the vicinity of the patchy Es layers even though the wind shear was relatively modest. An inversion in the MLT temperature profile contributed significantly to instability in the vicinity of one patchy layer. Of particular interest is the evidence for the conditions required for neutral convective instability in the lower-thermosphere region (which is usually associated with highly stable conditions) due to the rapid increase in temperature with altitude. A localized F-region plasma density enhancement associated with a sudden ascent up the magnetic field is shown to create the conditions necessary for convective plasma instability leading to the depletion plume and spread F. The growth time for the instability is short compared to the one described by Perkins (1973). This instability does not offer a simple analytic solution but is clearly present in numerical simulations. The instability mode has not been described previously but appears to be more viable than the various mechanisms that have been suggested previously as an explanation for the occurrence of midlatitude spread F