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Estimating the fate of oxygen ion outflow from the high-altitude cusp
Annales Geophysicae ( IF 1.9 ) Pub Date : 2020-04-08 , DOI: 10.5194/angeo-38-491-2020
Patrik Krcelic , Stein Haaland , Lukas Maes , Rikard Slapak , Audrey Schillings

Abstract. We have investigated the oxygen escape-to-capture ratio from the high-altitude cusp regions for various geomagnetic activity levels by combining EDI and CODIF measurements from the Cluster spacecraft. Using a magnetic field model, we traced the observed oxygen ions to one of three regions: plasma sheet, solar wind beyond a distant X-line or dayside magnetosheath. Our results indicate that 69 % of high-altitude oxygen escapes the magnetosphere, from which most escapes beyond the distant X-line (50 % of total oxygen flux). Convection of oxygen to the plasma sheet shows a strong dependence on geomagnetic activity. We used the Dst index as a proxy for geomagnetic storms and separated data into quiet conditions ( Dst>0 nT ), moderate conditions ( 0 > Dst > - 20 nT ), and active conditions ( Dst - 20 nT ). For quiet magnetospheric conditions we found increased escape due to low convection. For active magnetospheric conditions we found an increase in both parallel velocities and convection velocities, but the increase in convection velocities is higher, and thus most of the oxygen gets convected into the plasma sheet ( 73 %). The convected oxygen ions reach the plasma sheet in the distant tail, mostly beyond 50 RE .

中文翻译:

估计从高空风尖处流出的氧离子的归宿

摘要。我们通过结合来自集群航天器的 EDI 和 CODIF 测量,研究了各种地磁活动水平下高海拔尖端区域的氧气逸出与捕获比。使用磁场模型,我们将观察到的氧离子追踪到以下三个区域之一:等离子体片、远处 X 线以外的太阳风或日侧磁鞘。我们的结果表明,69% 的高空氧气逃逸到磁层,其中大部分逃逸到远处的 X 线之外(总氧通量的 50%)。氧气到等离子体片的对流显示出对地磁活动的强烈依赖。我们使用 Dst 指数作为地磁暴的代表,并将数据分为安静条件 (Dst>0 nT)、中等条件 (0 > Dst > - 20 nT) 和活跃条件 (Dst - 20 nT)。对于安静的磁层条件,我们发现由于低对流导致逃逸增加。对于活跃的磁层条件,我们发现平行速度和对流速度都增加,但对流速度的增加更高,因此大部分氧气通过对流进入等离子体层 (73 %)。对流氧离子到达远处尾部的等离子体片,大部分超过 50 RE 。
更新日期:2020-04-08
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