The dayside ultraviolet aurora and convection responses to a southward turning of the interplanetary magnetic field
The dayside ultraviolet aurora and convection responses to a southward turning of the interplanetary magnetic field
复制标题
白天紫外线极光和对流对行星际磁场南转的响应
DOI：
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发表时间：
2001
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通讯作者：
M. Brittnacher
中科院分区：
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作者：
K. McWilliams;T. Yeoman;J. Sigwarth;L. Frank;M. Brittnacher
抽象的。我们研究了大规模紫外线极光和对流对一系列通量转移事件的响应，这些事件是在 IMF 急剧且孤立的南转之后立即发生的。在感兴趣的时间间隔内，SuperDARN 正在监测北半球白天电离层的等离子体对流，而 VIS 地球相机和远紫外成像仪 (UVI) 正在监测北半球的紫外线极光。在 IMF 急剧南转后，在午后区域的 SuperDARN HF 雷达数据中看到了重新连接特征。 DMSP 航天器低空尖点中经典分散离子特征的测量结果支持了通量传递事件的存在。重新连接开始后，午后对流和紫外线极光同步扩大，半小时内达到18 MLT。发现极光椭圆在 16-18 MLT 扇区以对流速度向赤道移动，这意味着它与极热磁层边界直接相关。在本研究中，我们根据电离层等离子体对流速度的涡度估计了场对准电流对磁重联的响应。对流速度使用两种方法获得：（a）根据极光区相对较小区域中 SuperDARN HF 雷达对对流的双基地测量直接重建全矢量速度，以及（b）根据全球尺度球谐函数拟合从地图势模型推导出的 SuperDARN 速度。高涡度区域被预测为总场对准电流的一个组成部分的估计，与日侧紫外线极光的图像非常吻合，表明在这种情况下，等离子体涡度是日侧场对准电流（FAC）形态的出色估计器。午后扇区的极光和电离层电场的形态支持了响应于日面重新连接而引起的日面电流楔的存在。关键词。磁层物理学（极光现象；磁层-电离层相互作用；太阳风磁层-层相互作用）
Abstract. We examine the large-scale ultraviolet aurora and convection responses to a series of flux transfer events that immediately followed a sharp and isolated southward turning of the IMF. During the interval of interest, SuperDARN was monitoring the plasma convection in the dayside northern ionosphere, while the VIS Earth Camera and the Far Ul-traviolet Imager (UVI) were monitoring the northern hemisphere’s ultraviolet aurora. Reconnection signatures were seen in the SuperDARN HF radar data in the postnoon sector following a sharp southward turning of the IMF. The presence of flux transfer events is supported by measurements of a classic dispersed ion signature in the low-altitude cusp from the DMSP spacecraft. Subsequent to the onset of reconnection, the postnoon convection and ultraviolet aurora expanded in concert, reaching 18 MLT in half an hour. The auroral oval was found to move equatorward at the convection speed in the 16–18 MLT sector, implying that it was related directly to an adiaroic magnetospheric boundary. In the present study, we have estimated the field-aligned current response to magnetic reconnection in terms of the vorticity of the ionospheric plasma convection velocity. The convection velocities were obtained using two methods: (a) direct reconstruction of the full vector velocities from bistatic measurements of the convection by the SuperDARN HF radars in a relatively small region of the auroral zone, and (b) from global-scale spherical harmonic fits to the SuperDARN velocities deduced from the map potential model. Regions of high vorticity, which were predicted to be an estimate of a component of the total field-aligned current, agree extremely well with the images of the dayside UV aurora, indicating that, in this case, the plasma vorticity is an excellent estimator of the morphology of dayside field-aligned currents (FACs). The morphology of the aurora and ionospheric electric field in the postnoon sector supports the existence of a dayside current wedge induced in response to dayside reconnection. Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions; solar wind magne-tosphere interactions)