The event of 8 September 2017 was characterized by the effects of the arrival of two interplanetary coronal mass ejections on September 6th and 7th and a resultant geomagnetic storm. This storm event has been widely studied due to its extreme geo-effectiveness in the global geospace. In the inner magnetosphere, the effects included a distinct intensification of the ring current and a severely eroded plasmasphere. However, little attention has been paid to the role that the observed substorm injections played on the storm-time ring current. Starting at 1209 UT on September 8th, multiple substorm onsets occurred spreading over a wide magnetic local time range on the dawn side. Multiple substorm injections were observed simultaneously at geosynchronous orbit by the Los Alamos National Laboratory satellites and the Geostationary Operational Environmental Satellites, and by both the Exploration of energization and Radiation in Geospace/Arase and the Van Allen Probes missions deep in the inner magnetosphere. Subsequent buildup of the ring current was observed. In this study, we will investigate the role of the substorm injections on the extreme ring current response by numerical simulations with the physics-based Comprehensive Inner Magnetosphere-Ionosphere model using the geosynchronous data as boundary conditions to the model. Since the ring current has a strong influence on the inner magnetospheric dynamics, we also consider its impacts on the dynamics of the electric field and the plasmasphere. Furthermore, this study addresses the critical need to include substorms in evaluating the geo-effectiveness of geomagnetic storms.

We report on the solar and interplanetary (IP) causes of the third largest geomagnetic storm (2018 August 26) in solar cycle 24. The 2018 August 20 coronal mass ejection (CME) originating from a quiescent filament region becomes a magnetic cloud (MC) at 1 au after ~5 days. The CME accelerates for about a day as evidenced by the time evolution of the CME speed, the intensity of the associated post-eruption arcade, and the reconnected flux. The presence of multiple coronal holes near the filament channel and the high-speed wind from them seem to have the combined effect of producing complex rotation in the corona and IP medium resulting in a high-inclination MC. The Dst time profile in the main phase steepens significantly (rapid increase in storm intensity) coincident with the density increase in the MC second half of the MC. We confirm that the enhanced strength of the 2018 August 26 storm is a direct result of the enhanced MC density by comparing with two other events: the 2010 May 28 MC that has similar properties except for no density enhancement and the 2014 April 11 MC with a complex density structure. The Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model applied to the three events confirm that higher ring current energy results from larger dynamic pressure in the MCs. A complex temporal structure develops in the storm main phase if the underlying MC has a complex density structure during intervals of southward interplanetary magnetic field.

In a recent study by Shekhar et. al. 2021, a moderate geomagnetic storm (sym-H$\sim$-100 nT) during 28th-29th June 2013 was studied using CIMI (Comprehensive Inner Magnetosphere-Ionosphere) simulations and results were compared with TWINS (Two wide-angle Imaging Neutral-atom Spectrometers) observations. The CIMI simulations did not include ion injections. As a result, TWINS and CIMI results were found to disagree on the number and locations of ion pressure peaks and ion drift patterns. In this study, CIMI simulations were performed with the inclusion of ion injections using the geosynchronous particle flux data from 6 LANL satellites as boundary conditions. Comparisons of the spatial and temporal evolution of ring current (RC) ions including ion pressure, anisotropy, intensity and median energy, the ion spectrum at the ion pressure peak locations show improved agreements with TWINS observations, specifically in the recovery phase post 06 UT on 29th June, when rapid AE index fluctuations were observed.

The large-scale electric field in the inner magnetosphere is a key driver of many processes and the dynamics of magnetospheric plasmas. During geomagnetic storms, the enhanced convection electric field is responsible for eroding the plasmasphere and for moving the inner edge of the plasma sheet earthward. In this presentation, we show the preliminary results of an examination of the distribution and variations of the inner magnetospheric quasi-static electric field as measured by the Electric Field and Waves (EFW) instruments onboard the twin spacecraft of the Van Allen Probes mission. We investigate the role that the electric field plays in plasmasphere erosion and plasma sheet access to the inner magnetosphere by analyzing the electric field measurements in conjunction with cold plasma density and plasma sheet particle flux measurements. Since the coupling between plasma populations in the magnetosphere is inherently related to the electric field, we expect that the combined measurements of the electric field and plasmas will enhance our understanding of the physical processes that drive the magnetospheric dynamics.