Magnetospheric Multiscale observations of energetic oxygen ions at the duskside magnetopause during intense substorms

Chen Zeng,Suping Duan,Christopher Russell,Chi Wang,Roy Torbert,Lei Dai,Stephen Fuselier,James Burch,Barbara Giles

doi:10.5194/angeo-38-123-2020

Abstract

Abstract. Energetic oxygen ions (1–40 keV) observed by the Magnetospheric Multiscale (MMS) satellites at the duskside magnetopause boundary layer during phase 1 are investigated. There are 57 duskside magnetopause crossing events identified during intense substorms (AE>500 nT). These 57 events of energetic O+ at the duskside magnetopause include 26 events during the expansion phase and 31 events during the recovery phase of intense substorms. It is found that the O+ density in the duskside magnetopause boundary layer during the recovery phase (0.081 cm−3) is larger than that during the expansion phase (0.069 cm−3). The 26 events of energetic O+ ions at the duskside magnetopause during intense substorm expansion phase are all under the southward interplanetary magnetic field (IMF). There are only seven events under northward IMF, and they all occurred during the intense substorm recovery phase. The density of energetic O+ at the duskside magnetopause ranges from 0.007 to 0.599 cm−3. The maximum density of O+ occurred during the intense substorm recovery phase and under southward IMF. When the IMF is southward, the O+ density shows an exponential increase with the IMF Bz absolute value. Meanwhile, the O+/H+ density ratio shows an exponential growth with the IMF By. These results agree with previous studies in the near-Earth magnetosphere during intense substorm. It is suggested that O+ abundance in the duskside magnetopause boundary layer has a close relation to O+ variations in the near-Earth magnetosphere during intense substorms.

Highlights

Single charged oxygen ions (O+) in the magnetosphere are exclusively from the ionosphere
We investigate statistical features of energetic O+ at the duskside magnetopause and their relations to Auroral Electrojet (AE) index and solar wind conditions (e.g., interplanetary magnetic field (IMF) By, IMF Bz, and solar wind dynamic pressure) during the intense substorms (AE > 500 nT)
The AE index is defined as AE = Amplitude Upper (AU) − Amplitude Lower (AL)

Summary

Introduction

Single charged oxygen ions (O+) in the magnetosphere are exclusively from the ionosphere. Lennartsson and Shelley (1986) proposed that oxygen ions with energies less than 17 keV e−1 could provide 50 % of the density in the plasma sheet during disturbed geomagnetic activity. They found the increase in the O+ energy den-

Results

Discussion

Conclusion