Midday auroral breakup events and related energy and momentum transfer from the magnetosheath
Midday auroral breakup events and related energy and momentum transfer from the magnetosheath
复制标题
DOI：
10.1029/ja095ia02p01039
复制
发表时间：
1990-02
期刊：
影响因子：
--
通讯作者：
P. Sandholt;M. Lockwood;T. Oguti;S. Cowley;K. Freeman;B. Lybekk;A. Egeland;D. Willis
中科院分区：
文献类型：
--
作者：
P. Sandholt;M. Lockwood;T. Oguti;S. Cowley;K. Freeman;B. Lybekk;A. Egeland;D. Willis
通过利用太阳扫描光度计、全天空极光电视摄像机和EISCAT雷达进行的综合观测，可以详细分析正午极光分裂现象的时空发展以及71°-75°不变纬度雷达视场内的相关电离层离子流模式。雷达数据显示，在这里报告的两个不同事件期间，主要向北和向西的离子漂移，其幅度接近于离散瞬时极光形式的相应速度，其特征在于IMF| BY/BZ| 2（IMF BZ在−8和−3 nT之间，BY > 0）。离散光学事件的空间尺度为北纬150 km，东经1500 km，它们的寿命小于10 min。推测在IMF中，沿离散弧沿着有电位增强，峰值在30-50 kV范围内|BY/BZ| 2个病例。根据光度计强度和离子漂移数据，估算出离散结构最大相位的焦耳热耗散率为100尔格cm-2 s-1（0.1 W m-2）。这些观察结果与事件的其他特征相结合，记录在这里和最近的几项研究中（即，它们的准周期性质，它们相对于持续的尖点或裂缝极光弧的运动模式，与行星际磁场和相关的离子漂移/E场事件和地磁特征的强烈关系，被认为是支持瞬变的有力证据，极顶磁层顶间歇性重联过程及与之相关的极尖和极裂电离层能量和动量转移地区光学特征的空间结构和光谱特征表明，在最强烈的极光事件期间，磁层顶和电离层之间存在着相关的局部化的10 - 1千伏电位降。事件的持续时间比较以及与通量传输事件相关的电流管的预测特征时间的动量传输到电离层。这表明，在这2-10分钟的时间间隔后，鞘粒子不能再到达电离层下的开放通量管，由于随后的超阿尔文流沿着磁层顶，电导率较低，少得多的动量从太阳风中提取的电离层。昼侧极光破裂事件的重现时间（3-15 min）和当地时间分布（0.0900 -1500 MLT）结合上述信息，表明了磁层顶瞬变重联和极尖裂区在太阳风与磁层之间动量和能量传递中的重要作用。
Combined observations by meridian-scanning photometers, all-sky auroral TV camera and the EISCAT radar permitted a detailed analysis of the temporal and spatial development of the midday auroral breakup phenomenon and the related ionospheric ion flow pattern within the 71°–75° invariant latitude radar field of view. The radar data revealed dominating northward and westward ion drifts, of magnitudes close to the corresponding velocities of the discrete, transient auroral forms, during the two different events reported here, characterized by IMF |BY/BZ| 2, respectively (IMF BZ between −8 and −3 nT and BY > 0). The spatial scales of the discrete optical events were ∼50 km in latitude by ∼500 km in longitude, and their lifetimes were less than 10 min. Electric potential enhancements with peak values in the 30–50 kV range are inferred along the discrete arc in the IMF |BY/BZ| 2 case. Joule heat dissipation rates in the maximum phase of the discrete structures of ∼ 100 ergs cm−2 s−1 (0.1 W m−2) are estimated from the photometer intensities and the ion drift data. These observations combined with the additional characteristics of the events, documented here and in several recent studies (i.e., their quasi-periodic nature, their motion pattern relative to the persistent cusp or cleft auroral arc, the strong relationship with the interplanetary magnetic field and the associated ion drift/E field events and ground magnetic signatures), are considered to be strong evidence in favour of a transient, intermittent reconnection process at the dayside magnetopause and associated energy and momentum transfer to the ionosphere in the polar cusp and cleft regions. The filamentary spatial structure and the spectral characteristics of the optical signature indicate associated localized ˜1-kV potential drops between the magnetopause and the ionosphere during the most intense auroral events. The duration of the events compares well with the predicted characteristic times of momentum transfer to the ionosphere associated with the flux transfer event-related current tubes. It is suggested that, after this 2–10 min interval, the sheath particles can no longer reach the ionosphere down the open flux tube, due to the subsequent super-Alfvenic flow along the magnetopause, conductivities are lower and much less momentum is extracted from the solar wind by the ionosphere. The recurrence time (3–15 min) and the local time distribution (∼0900–1500 MLT) of the dayside auroral breakup events, combined with the above information, indicate the important roles of transient magnetopause reconnection and the polar cusp and cleft regions in the transfer of momentum and energy between the solar wind and the magnetosphere.