Mesoscale dayside convection vortices and their relation to substorm phase
Mesoscale dayside convection vortices and their relation to substorm phase
复制标题
中尺度昼侧对流涡及其与亚暴相的关系
DOI：
10.1029/96ja01639
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发表时间：
1996
影响因子：
--
通讯作者：
L. Frank
中科院分区：
文献类型：
--
作者：
R. Greenwald;J. Ruohoniemi;W. Bristow;G. Sofko;J. Villain;A. Huuskonen;S. Kokubun;L. Frank
用超级双极光雷达网（SuperDARN）的前两对北方半球组成部分进行的测量表明，在高纬度午后电离层中间歇性地存在一个中尺度对流涡旋。涡旋是亚暴发展阶段的一个特征，其中心通常位于1430至1530 MLT之间，不变纬度为75°至80°。它的直径从几百到1000公里不等，相关的电位降为5-10千伏。涡旋的中心是一个间接向上的场向电流，估计幅度接近3 μA/m2。涡旋的中心位置在黄昏对流单体的向阳端附近，正好在向阳对流等离子体的极向方向，正好在向阳对流等离子体急剧向极旋转并进入极冠的区域的黄昏方向。当等离子体向极对流时，它会穿过一个不规则区域，该区域与尖点的电离层足迹有关。该涡旋的一个显著特征是，它在午夜扇区的亚暴扩张阶段开始时同时消失。几个磁层源机制，包括开尔文-亥姆霍兹和撕裂模不稳定性，通量传输事件，和宏观电流系统，已被认为是涡旋。最好的解释似乎是，旋涡与对流场对齐的电流，驱动的跨极冠电位和关闭作为彼得森电流通过尖点区域。在膨胀阶段开始后，涡旋消失，这是由于亚暴膨胀期间夜面电导率显着增加，导致磁层闭合电流重定向。
Measurements made with the first two pairs of the northern hemisphere component of the Super Dual Auroral Radar Network (SuperDARN) have revealed the intermittent existence of a mesoscale convection vortex in the high-latitude postnoon ionosphere. The vortex is a feature of the substorm growth phase and is typically centered between 1430 and 1530 MLT and 75° and 80° invariant latitude. It has a diameter ranging from a few hundred to ∼1000 km and an associated potential drop of 5–10 kV. The vortex is centered on a filamentary upward field-aligned current with an estimated magnitude approaching 3 μA/m2. The vortex is centered near the sunward end of the dusk convection cell just poleward of the sunward convecting plasma and just duskward of the region where the sunward convecting plasma rotates sharply poleward and enters the polar cap. As the plasma convects poleward, it passes through an irregularity zone that has been associated with the ionospheric footprint of the cusp. A remarkable feature of the vortex is that it disappears concurrently with the onset of a substorm expansion phase in the midnight sector. Several magnetospheric source mechanisms, including the Kelvin-Helmholtz and tearing mode instabilities, flux transfer events, and macroscale current systems, have been considered for the vortex. The best explanation appears to be that the vortices are associated with filamentary field-aligned currents that are driven by the cross polar cap potential and close as Pedersen currents through the cusp region. The disappearance of the vortex following the onset of an expansion phase is attributed to a redirection of magnetospheric closure currents as a consequence of the significant increase in nightside conductivity during a substorm expansion.