The source of O⁺ in the storm time ring current

Abstract

A stretched and compressed geomagnetic field occurred during the main phase of a geomagnetic storm on 1 June 2013. During the storm the Van Allen Probes spacecraft made measurements of the plasma sheet boundary layer and observed large fluxes of O+ ions streaming up the field line from the nightside auroral region. Prior to the storm main phase there was an increase in the hot (>1 keV) and more isotropic O+ ions in the plasma sheet. In the spacecraft inbound pass through the ring current region during the storm main phase, the H+ and O+ ions were significantly enhanced. We show that this enhanced inner magnetosphere ring current population is due to the inward adiabatic convection of the plasma sheet ion population. The energy range of the O+ ion plasma sheet that impacts the ring current most is found to be from ~5 to 60 keV. This is in the energy range of the hot population that increased prior to the start of the storm main phase, and the ion fluxes in this energy range only increase slightly during the extended outflow time interval. Thus, the auroral outflow does not have a significant impact on the ring current during the main phase. The auroral outflow is transported to the inner magnetosphere but does not reach high enough energies to affect the energy density. We conclude that the more energetic O+ that entered the plasma sheet prior to the main phase and that dominates the ring current is likely from the cusp.

Ion Trapping and Acceleration at Dipolarization Fronts: High‐Resolution MHD and Test‐Particle Simulations

“…Observational analyses (e.g., Kistler et al, ; Runov et al, ) suggest that ion acceleration in the course of their inward transport from the tail into the inner magnetosphere is approximately adiabatic, that is, conserves their first adiabatic invariant (Alfvén, ): where m is the ion mass, p ⊥ is the momentum component and K ⊥ is the kinetic energy perpendicular to the magnetic field at the ion gyrocenter, and B is the magnetic field amplitude. The second approximate equality is valid for nonrelativistic particles with perpendicular energy substantially exceeding the pickup energy, , which for the plasma sheet protons is of the order of several kiloelectron volts.…”

The role of convection in the buildup of the ring current pressure during the 17 March 2013 storm

“…This same technique was used in Kistler et al . []. Since mu is a function of the perpendicular energy, we use 90° pitch angle data for all spectra plotted versus mu.…”

“…We can therefore identify adiabatic transport by identifying conservation of the distribution function at constant mu for decreasing L shells. A similar procedure was used by Kistler et al [2016].…”

Space Weather Effects Produced by the Ring Current Particles

“…Although, the early measurements of the ring current particles were made onboard OGO 3 (e.g., Frank 1967), Explorer 45 (e.g., Smith and Hoffman 1974) and CRRES missions (e.g., Grande et al 1997;Friedel and Korth 1997), the first mission, which clarified the detailed picture of the ring current energy and composition was the AMPTE mission of the late 1980s (e.g., Lui et al 1987;Lui and Hamilton 1992;De Michelis et al 1997). Extensive observations of the ring current were done by the most recent Van Allen Probes mission (e.g., Zhao et al 2015;Gkioulidou et al 2016;Kistler et al 2016;Shi et al 2016;Menz et al 2017). …”