A Comparison of Conjugate Auroral Electojet Indices

The auroral electrojet index (AE) is used as an indicator of geomagnetic activity at high latitudes representing the strength of auroral electrojet currents in the Northern polar ionosphere. A similar AE index for the Southern hemisphere is not available due to lack of complete coverage the Southern auroral zone (half of which extends over the ocean) with continuous magnetometer observations. While in general global auroral phenomena are expected to be conjugate, differences have been observed in the conjugate observations from the ground and from the Earth's satellites. These differences indicate a need for an equivalent Southern auroral geomagnetic activity index. The goal of this award is to create the Southern AE (SAE) index that would accurately reflect auroral activity in that hemisphere. With this index, it would be possible to investigate the similarities and the cause of differences between the SAE and 'standard' AE index from the Northern hemisphere. It would also make it possible to identify when the SAE does not provide a reliable calculation of the Southern hemisphere activity, and to determine when it is statistically beneficial to consider the SAE index in addition to the standard AE while analyzing geospace data from the Northern and Southern polar regions. The study will address these questions by creating the SAE index and its 'near-conjugate' NAE index from collected Antarctic magnetometer data, and will analyze variations in the cross-correlation of these indices and their differences as a function of geomagnetic activity, season, Universal Time, Magnetic Local Time, and interplanetary magnetic field and solar wind plasma parameters. The broader impact resulting from the proposed effort is in its importance to the worldwide geospace scientific community that currently uses only the standard AE index in a variety of geospace models as necessary input.

极光电射流指数（auroral electrojet index, AE）常被用作高纬度地磁活动的观测指标，用以表征北极高层电离层内极光电射流的强度。由于南半球极光带（其中近半数区域覆盖海洋）缺乏连续的磁力仪观测数据，目前尚无适用于南半球的同类AE指数。尽管全球极光现象普遍被认为具有共轭对称性，但基于地面与地球卫星的共轭观测中已发现存在显著差异。这些差异表明，亟需构建等效的南半球极光地磁活动指数。本科研资助项目的目标是构建南半球AE（SAE）指数，以精准反映该半球的极光活动水平。借助该指数，研究人员可探究南半球SAE指数与北半球“标准”AE指数之间的相似性，以及二者产生差异的成因；同时，该指数还可用于识别何时SAE无法可靠计算南半球极光活动，并可确定在分析南北极地区的地球空间数据时，在何种统计条件下额外引入SAE指数会更具分析价值。本研究将通过整合已采集的南极磁力仪观测数据，构建SAE指数及其“近共轭”北半球AE（Northern AE, NAE）指数，并分析两类指数的互相关变化、二者差异随地磁活动、季节、世界时（Universal Time, UT）、磁地方时（Magnetic Local Time, MLT）以及行星际磁场与太阳风等离子体参数的演化规律。本研究的潜在学术与应用价值在于，其对当前仅将标准AE指数作为各类地球空间模型必要输入参数的全球地球空间科学共同体具有重要意义。