[P-EM11] Dynamics of the Inner Magnetospheric System

[PEM11-P04] Time variations of molecular ions in the inner magnetosphere observed by Arase

*永谷 朱佳理¹、三好 由純¹、浅村 和史²、中村 紗都子¹、小路 真史¹、Lynn Kistler³、篠原 育² (1.名古屋大学宇宙地球環境研究所、2.宇宙航空研究開発機構/宇宙科学研究所、3.University of New Hampshire Main Campus)

In the Earth’s magnetosphere, there are several kind of ions originated from both the solar wind and the ionosphere and molecular ions in the magnetosphere are originated in the Earth’s ionosphere. Observations about molecular ions are not enough compared with other ion observations, and the mechanism of the outflow from the ionosphere as well as the long-term variations are not well known. The Arase satellite has observed various kinds of ions since 2017 and two ion analyzers LEPi and MEPi cover energy range from 10 eV/q to 180 keV/q. Using the data from the MEPi instrument, variations of molecular ions to the magnetic storms and solar wind conditions are investigated [Seki+, 2019], and molecular ions are often observed in the inner magnetosphere even small magnetic storms. In this study, we analyzed the time-of-flight (TOF) data from the LEPi [Asaramura+, 2018] to investigate variations of molecular ions in the inner magnetosphere and their dependence about magnetic storms and solar wind conditions. LEPi covers the energy range from 10 eV/q to 25 keV/q and counts as function of energy and TOF are obtained every 16 seconds. The TOF measurements of LEPi have been operated in the outbound pass every 4 revolutions around the Earth. In the analysis, we estimate counts of molecular ions by fitting the empirical functions for TOF profile using the non-linear least square method. The estimated counts were calibrated by the time variations of efficiency of the LEPi instrument. Using the data set, we investigated timevariations of molecular ions in the inner magnetosphere and found that enhancement of molecular ions takes place associated with magnetic storms, which is consistent with the previous studies. The molecular ions are found in not only severe magnetic storms but small storm activities of ~ 30 nT, which suggests that molecular ions frequently escape from the Earth ionosphere event in geomagnetically weak conditions.