The impact of storm-time ion composition changes in the near-earth plasma sheet on ring current pressure development

Using Van Allen Probe observations of the inner magnetosphere, it was found that the largest difference between the ICME and CIR ring current responses during the storm main and early-recovery phases is the difference in the response of the ~ < 55 keV O⁺to these drivers (Mouikis et al., 2019) . While the H⁺pressureresponse shows similar source and convection patterns for ICME and CIR storms, the O ⁺pressure response is significantly stronger for ICME storms. In addition, the ICME O⁺pressure increases more strongly than the H⁺pressure with decreasing L, and peaks at L ~ 3.5 - 4. This preferential enhancement of O⁺over H⁺could be due to differences in their energy spectrum in the source population (at ~ 6 R_Enightside plasma sheet), differences in the source time dependence for the two species, or both (Menz et al., 2017). To test the above hypothesis, we use Van Allen Probes and MMS ion composition data from the nightside plasma sheet, ~5 - 8 Re, to study the source region H+ and O+ energy spectra and their time development for individual storms. Subsequently, these observations are used as inputs to the CIMI inner magnetosphere model (Fok et al., 2016) to test under which conditions the distinct O+ pressure peak can be reproduced.