Characteristics of O+ Outflow during Sawtooth Events

Abstract:

Sawtooth events are repeated injections of energetic particles at geosynchronous orbit. Simulations have suggested that heavy ions like O⁺ may play a role in increasing the pressure and causing the magnetic tail to stretch and then relax, creating the periodic injections. However, in some cases (e.g. Brambles et al., 2011) the outflow came from the nightside, and a feedback mechanism drove the periodicity. In another case (Zhang et al. 2020) the sawtooth events were driven by steady cusp outflow. To examine the role of the cusp and nightside outflow during these events, we examine how the outflow varies during sawtooth events to determine if there is evidence for a feedback mechanism, and to compare the magnitude of the outflow at different local times. We perform a superposed epoch analysis of the ion outflow using the recalibrated TEAMS (Time-of-Flight Energy Angle Mass Spectrograph) data from the FAST spacecraft. Using the time period from 1996-2007 provides 56 ICME-driven sawtooth events and 46 SIR-driven sawtooth events. In this study, the variations of H⁺ and O⁺ outflow relative to the "tooth" onset times are determined in 4 local time quadrants centered on midnight, dawn, noon, and dusk. Comparing the nightside and the dayside outflow, and how that outflow varies with time during the sawtooth event for the two types of storms will help to clarify the role of O+ outflow in driving the events.