Does Ring Current Heating Generate the Observed O⁺ Shell?

Abstract

The Naval Research Laboratory (NRL) Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere code is used to examine the effect of ring current heating during a storm. With a ring current heating function added to SAMI3, a cold thermal (<1 eV) oxygen ion outflow is produced, with O+ density and location similar to observations of the so‐called “oxygen torus.” The ring current heating function is based on a Comprehensive Inner Magnetosphere‐Ionosphere (CIMI) model simulation of the 7 October 2015 storm. We find that the ring current can heat plasmasphere electrons, subsequently heating plasmasphere H+, and ionosphere O+. The resulting O+ outflows resemble observed O+ enhancements in the inner magnetosphere.

Counterstreaming Cold H+, He+, O+, and N+ Outflows in the Plasmasphere

“…We then modified the code to implement two-fluid H + and repeated the simulation. As expected, the new SAMI3 run of the same storm is virtually identical to that presented in Krall et al (2020). Because, as we shall see below, the effect of counterstreaming is not dramatic, results from the new two-stream SAMI3 run are also quite similar to those presented in Krall et al (2020).…”

“…As expected, the new SAMI3 run of the same storm is virtually identical to that presented in Krall et al (2020). Because, as we shall see below, the effect of counterstreaming is not dramatic, results from the new two-stream SAMI3 run are also quite similar to those presented in Krall et al (2020). However, our attention in that prior work was on O + , not H + .…”

“…We consider SAMI3 simulations of a specific storm event, including plasmasphere erosion, refilling, and H + , He + , N + and O + outflows. In these simulations, O + (and N + ) outflows are driven by ring-current heating, as in Krall et al (Krall et al, 2020). These results confirm past findings (Roberts et al, 1987;Craven et al, 1995) that the He + density generally mimics H + (Craven et al, 1997;Goldstein et al, 2003) and that N + generally mimics O + (Ilie and Liemohn, 2016).…”

“…The storm simulated here is the same as that in Krall et al (2020). To ensure that the only differences between SAMI3 and two-stream SAMI3 reflect an updated treatment of the H + ions, we began by repeating that previous work with the latest version of the SAMI3 code.…”

“…In addition to the EUV indices already described, the Kp index is used to determine the stormtime convection potential as in Volland (Volland, 1973), Stern (Stern, 1975) and Maynard and Chen (Maynard and Chen, 1975). The Dst index is used to determine ring-current heating of ionosphere and plasmasphere electrons as in Krall et al (Krall et al, 2020).…”