Signatures of the midnight open-closed magnetic field line boundary during balanced dayside and nightside reconnection
Signatures of the midnight open-closed magnetic field line boundary during balanced dayside and nightside reconnection
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昼夜平衡重联期间午夜开闭磁力线边界的特征
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发表时间：
2002
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通讯作者：
P. Wilkinson
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作者：
M. Parkinson;P. Dyson;M. Pinnock;J. Devlin;M. Hairston;E. Yizengaw;P. Wilkinson
1999 年 12 月 10 日的磁午夜期间，地磁条件受到中度干扰（K-p=2），当时塔斯曼国际地球空间环境雷达（TIGER）（南半球高频 SuperDARN 雷达）观察到频谱宽度在接近 69°A 处出现持续、急剧的纬度下降（大约 90 公里）。跨越该谱宽边界 (SWB) 的视线多普勒速度也迅速下降。 SWB极地区域的特征是高光谱宽度（> 200 m/s），并且开始爆发赤道和东向气流（> 500 m/s），并迅速向赤道扩展。通过将 TIGER 数据与国防气象卫星计划 (DMSP) F14 卫星上测量的降水粒子计算出的频谱图进行比较，推断出熟悉的电离层和磁层区域之间的关系。经常观察到高光谱宽度散射，在今晚，它与将极冠电离层穿过至南尾叶的开放（但很快将重新连接）场线上形成的不规则性有关。 SWB 赤道方向的区域具有非常低的谱宽 (<50 m/s) 和通常更慢、更多的纬向流 (<300m/s) 的特点。这种散射更加短暂，并且与封闭场线上的不规则性相关，该封闭场线上将离散且扩散的极光椭圆形穿过等离子体片边界层（PSBL）和中央等离子体片（CPS）。因此，SWB 是开闭场线边界的合理代表，并且该区域的赤道方向限制（具有低谱宽）可能与主电离层槽的极向壁对齐。据观察，SWB 在大约 10 分钟的时间尺度上向极地收缩并向赤道扩张，这与白天和夜间平衡重新连接期间的预期非常相似。在麦格理岛（-65°A）和霍巴特（-54°A）进行的总电子含量（TEC）测量，以及在同一站点以及邦杜拉（-49°A）记录的电离图也有助于验证这一解释。
The geomagnetic conditions were moderately disturbed (K-p=2) during magnetic midnight on 10 December 1999, when the Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar, observed a persistent, sharp latitudinal decrease (similar to90km) in spectral width near similar to69degreesA. The line-of-sight Doppler velocity also rapidly declined across this spectral width boundary (SWB). The region poleward of the SWB was characterized by high spectral widths (> 200 m/s), and the start of bursty equatorward and eastward flows (>500 m/s), which rapidly expanded equatorward. The relationships between familiar ionospheric and magnetospheric regions were inferred by comparing TIGER data with spectrograms calculated from precipitating particles measured on board the Defence Meteorology Satellite Program (DMSP) F14 satellite. The high spectral width scatter is often observed, and on this evening it was associated with irregularities forming on the open (but soon to be reconnected) field lines threading the polar cap ionosphere to the southern tail lobe. The region equatorward of the SWB was characterized by very low spectral widths (<50 m/s) and generally slower, more zonal flows (<300m/s). This kind of scatter is more transient, and was associated with irregularities residing on the closed field lines threading the discrete and diffuse auroral oval to the plasma sheet boundary layer (PSBL) and central plasma sheet (CPS). Hence, the SWB was a reasonable proxy for the open-closed field line boundary, and the equatorward limit of the region, with low spectral width, was probably aligned with the poleward wall of the main ionospheric trough. The SWB was observed to contract poleward and expand equatorward on time scales of similar to10 min, much as would be expected during balanced dayside and nightside reconnection. Total electron content (TEC) measurements made at Macquarie Island (-65degreesA) and Hobart (-54degreesA), and the ionograms recorded at the same stations, as well as at Bundoora (-49degreesA), also helped to validate the interpretation.