SuperDARN Evidence for Convection‐Driven Lagrangian Coherent Structures in the Polar Ionosphere
SuperDARN Evidence for Convection‐Driven Lagrangian Coherent Structures in the Polar Ionosphere
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DOI：
10.1029/2018ja026225
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发表时间：
2019-05
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影响因子：
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通讯作者：
U. Ramirez;Ningchao Wang;A. Chartier;S. Datta‐Barua
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作者：
U. Ramirez;Ningchao Wang;A. Chartier;S. Datta‐Barua
极冠斑块是数百公里尺度上的等离子体密度的大的零星增强，其可以影响全球导航卫星系统的性能。拉格朗日相干结构（LCS）是在时间演化流中显示最大分离区域的脊。先前基于电离层流动模型的工作表明，LCS存在于电离层中，并且是控制斑块形成的障碍。在这项工作中，我们使用超级双极光雷达网络（SuperDARN）离子对流场确定了高纬度电离层中的第一个数据驱动的LCS。在地磁平静期和活跃期，对使用电离层-热层算法发现的LCS进行了比较。LCS的形状被发现是依赖于电位模式。一致的双细胞模式导致W形LCS，但是当双细胞模式分解时，LCS失去了这种特征形状。电势的变化，以及LCS的变化，可能是由于行星际磁场的变化。从经验模型和数据获得的LCS之间的比较表明，数据驱动的LCS是极向的，并且具有比基于模型的LCS更短的纵向跨度。2015年3月17日LCS位置和极帽斑块形成的比较表明，斑块中心是由主LCS脊上的等离子体形成的，这一点在2011年9月26日的单独极帽斑块事件中得到证实。
Polar cap patches are large sporadic enhancements of plasma density on the scale of hundreds of kilometers, which can impact the performance of Global Navigation Satellite Systems. Lagrangian Coherent Structures (LCSs) are ridges that show areas of maximal separation in a time‐evolving flow. Previous work based on modeled ionospheric flow showed that LCSs exist in the ionosphere and are barriers governing patch formation. In this work, we identify the first data‐driven LCSs in the high‐latitude ionosphere using Super Dual Auroral Radar Network (SuperDARN) ion convection fields. The LCSs found using the Ionosphere‐Thermosphere Algorithm for LCSs are compared during geomagnetically quiet and active periods. The shape of the LCS is found to be dependent on the electric potential pattern. A consistent two‐cell pattern results in a W‐shaped LCS, but when the two‐cell pattern breaks down, the LCS loses this characteristic shape. The changes in the electric potential, and thus the LCS, are likely due to changes in the interplanetary magnetic field. A comparison between LCSs obtained from empirical models and data reveal that the data‐driven LCSs are poleward of and have a shorter longitudinal span than the model‐based LCSs. A comparison of the LCS location and the formation of a polar cap patch on 17 March 2015 showed that the center of the patch developed from plasma on the main LCS ridge, and this is confirmed with a separate polar cap patch event from 26 September 2011.