MMS observations of energetic oxygen ions at the low-latitude duskside magnetopause during intense substorms
Abstract. Energetic oxygen ions O+ (> 1 keV) observed by the Magnetospheric Multiscale (MMS) satellites at the dusk flank magnetopause during the phase 1a and 1b are investigated. There are 31 dusk flank magnetopause crossing events during intense substorms (AE > 500 nT) are identified. These 31 events of energetic O+ at the dusk flank magnetopause include 9 events during the expansion phase and 22 events during the recovery phase of intense substorms. It is noted that 9 events of energetic O+ ion at the dusk flank magnetopause during intense substorms expansion phase are all under the southward IMF conditions. The number density of energetic O+ at the dusk flank magnetopause ranges from 0.01 cm−3 to 0.2 cm−3. The maximum number density ratio of O+/H+ is ~ 0.055 during intense substorm recovery phase with AE index about 610 nT and under the northward interplanetary magnetic field (IMF). The number density ratio of O+/H+ also shows an exponential increase with the IMF By. While IMF Bz seems play a minor role in O+ abundance at the dusk flank magnetopause during intense substrom. Our observations suggest that energetic oxygen ions play a key role in the mass and energy transferring from the tail to the dayside in the magnetosphere during intense substorms.