Comparison of CIMI Simulations and TWINS Observations on June 28 and 29, 2013
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A moderate geomagnetic storm (Sym/H similar to-100 nT) during June 28 and 29, 2013 was studied using Comprehensive Inner Magnetosphere-Ionosphere (CIMI) simulations and results were compared with Two wide-angle Imaging Neutral-atom Spectrometers (TWINS) observations of the spatial and temporal evolution of ring current (RC) ions including ion pressure, anisotropy, intensity, and median energy. At the onset of the storm (11:00 UT on June 28), TWINS ion pressure peaks were located radially outward and dusk ward compared to CIMI. During the main phase and the recovery phase (06:00 UT on June 28 to 16:00 UT on June 29), southward IMF Bz and rapid AE index fluctuations were observed indicating substorm ion injections and TWINS observed multiple ion pressure peaks at least one of which were found to be close to the locations of CIMI ion pressure peaks. TWINS also observed regions of parallel pressure anisotropy near pre-midnight sectors. The RC ion energies in TWINS were found to be very low (<10 keV) indicating convective transport of O+ ions. When the storm had nearly recovered post 17:00 UT on June 29, TWINS and CIMI observed single pressure peaks but TWINS ion pressure peaks were radially outward compared to CIMI. Also, the spatial profiles of TWINS ion energies showed gradual removal of low-energy ions. Over all, TWINS and CIMI results were found to agree on the general features of the RC. However, effects of shielding electric fields, particle injections, and presence of O+ ions were more prominent in TWINS data.