Typical auroral substorm: A bifurcated oval
Typical auroral substorm: A bifurcated oval
复制标题
典型的极光亚暴：分叉椭圆形
DOI：
--
复制
发表时间：
2007
期刊：
影响因子：
--
通讯作者：
J. Baker
中科院分区：
文献类型：
--
作者：
J. Gjerloev;R. Hoffman;J. Sigwarth;L. Frank;J. Baker
[1]利用极地可见光成像系统地球相机拍摄的全球极光图像，分析了116个极光亚暴的紫外辐射。所选择的事件是相当孤立的，必须从局部发病扩大。结果发现，基本上所有满足这些简单标准的极光事件都会扩展为Akasofu（1964）的膨胀型极光。平均极光发射模式，汇编了11个时间步长的亚暴覆盖20分钟前的发病，直到进入恢复阶段。这一汇编需要一个三步骤的标准化技术，一个时间的基础上扩展的时间和两个空间，磁当地时间和纬度。这些平均模式，然后适合于一个单一或双重高斯分布的纬度为24个磁当地时间。在此分析的基础上，我们得出了以下结论。标准化技术是非常有效的，在保持个人极光发射模式的关键功能，即使个别事件的强度，大小，位置和寿命显着变化。因此，我们的归一化结果定量地验证了Akasofu（1964）的假设，即在膨胀型极光亚暴中存在关键的极光特征。亚暴爆发后，极光椭圆形明显分为两部分：椭圆形极光在发病前椭圆形的纬度范围内，主要在午夜后向东扩展，而隆起极光则出现在椭圆形之外，在MLT中向两极和东西方向扩展。椭圆形的极光衰减速度比隆起的辐射快，表明衰减有不同的时间常数。由于这两个极光分量的时空行为有明显的差异，我们认为它们的来源是准独立的。
[1] Utilizing global auroral images obtained by Polar Visible Imaging System Earth Camera, we have analyzed the UV emissions from 116 auroral substorms. The events selected were fairly isolated and had to expand from a localized onset. It was found that essentially all auroral events fulfilling these simple criteria expand into the Akasofu (1964) bulge-type aurora. Averaged auroral emission patterns were compiled for 11 time steps of the substorm covering 20 min prior to the onset until well into the recovery phase. This compilation required a three-step normalization technique, one temporal based on the expansion time and two spatial, magnetic local time and latitude. These average patterns were then fit to either a single or double Gaussian distribution in latitude for each of 24 magnetic local times. On the basis of this analysis we made the following conclusions. The normalization technique is highly efficient in maintaining the key features in the individual auroral emission patterns, even though the individual events varied significantly in intensity, size, position, and lifetime. Thus our normalization results quantitatively validate the Akasofu (1964) assumption that key auroral features exist in the bulge-type auroral substorm. After the substorm onset the auroral oval becomes clearly bifurcated consisting of two components: the oval aurora in the latitude range of the preonset oval and expanding primarily eastward postmidnight, and the bulge aurora, which emerges out of the oval, expanding poleward and both east and west in MLT. The oval aurora decay faster than the bulge emissions indicating that the decays have separate time constants. Owing to the pronounced difference in the spatiotemporal behavior of the two auroral components we suggest that their sources are quasi-independent.