Kitamura Naritoshi, Seki Kanako, Keika Kunihiro, Nishimura Yukitoshi, Hori Tomoaki, Hirahara Masafumi, Lund Eric J, Kistler Lynn M, Strangeway Robert J
Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
Department of Electrical and Computer Engineering and Center for Space Physics, Boston University, Boston, MA USA.
Earth Planets Space. 2021;73(1):202. doi: 10.1186/s40623-021-01532-y. Epub 2021 Nov 6.
The ionosphere is one of the important sources for magnetospheric plasma, particularly for heavy ions with low charge states. We investigate the effect of solar illumination on the number flux of ion outflow using data obtained by the Fast Auroral SnapshoT (FAST) satellite at 3000-4150 km altitude from 7 January 1998 to 5 February 1999. We derive empirical formulas between energy inputs and outflowing ion number fluxes for various solar zenith angle ranges. We found that the outflowing ion number flux under sunlit conditions increases more steeply with increasing electron density in the loss cone or with increasing precipitating electron density (> 50 eV), compared to the ion flux under dark conditions. Under ionospheric dark conditions, weak electron precipitation can drive ion outflow with small averaged fluxes (~ 10 cm s). The slopes of relations between the Poynting fluxes and outflowing ion number fluxes show no clear dependence on the solar zenith angle. Intense ion outflow events (> 10 cm s) occur mostly under sunlit conditions (solar zenith angle < 90°). Thus, it is presumably difficult to drive intense ion outflows under dark conditions, because of a lack of the solar illumination (low ionospheric density and/or small scale height owing to low plasma temperature).
电离层是磁层等离子体的重要来源之一，尤其是对于低电荷态的重离子。我们利用快速极光快照（FAST）卫星在1998年1月7日至1999年2月5日期间在3000 - 4150千米高度获取的数据，研究了太阳光照对离子流出数通量的影响。我们推导了不同太阳天顶角范围内能量输入与流出离子数通量之间的经验公式。我们发现，与黑暗条件下的离子通量相比，在阳光照射条件下，流出离子数通量随损失锥中电子密度的增加或随沉淀电子密度（> 50电子伏特）的增加而更陡峭地增加。在电离层黑暗条件下，弱电子沉淀可以驱动平均通量较小（约10厘米每秒）的离子流出。坡印廷通量与流出离子数通量之间关系的斜率对太阳天顶角没有明显的依赖性。强烈的离子流出事件（> 10厘米每秒）大多发生在阳光照射条件下（太阳天顶角 < 90°）。因此，由于缺乏太阳光照（由于等离子体温度低导致电离层密度低和/或标高小），在黑暗条件下可能难以驱动强烈的离子流出。
