Understanding storm‐time ring current development through data‐model comparisons of a moderate storm

With three components, global magnetosphere (GM), inner magnetosphere (IM), and ionospheric electrodynamics (IE), in the Space Weather Modeling Framework (SWMF), the moderate storm on 19 May 2002 is globally simulated over a 24‐hour period that includes the sudden storm commencement (SSC), initial phase, and main phase of the storm. Simulation results are validated by comparison with in situ observations from Geotail, GOES 8, GOES 10, Polar, LANL MPA, and the Sym ‐ H and Dst indices. It is shown that the SWMF is reaching a sophistication level for allowing quantitative comparison with the observations. Major storm characteristics at the SSC, in the initial phase, and in the main phase are successfully reproduced. The simulated plasma parameters exhibit obvious dawn‐dusk asymmetries or symmetries in the ring current region: higher density near the dawn and higher temperature in the afternoon and premidnight sectors; the pressure is highest on the nightside and exhibits a near dawn‐dusk symmetry. In addition, it is found in this global modeling that the upstream solar wind/IMF conditions control the storm activity and an important plasma source of the ring current is in the solar wind. However, the ionospheric outflow can also affect the ring current development, especially in the main phase. Activity in the high‐latitude ionosphere is also produced reasonably well. However, the modeled cross polar cap potential drop (CPCP) in the Southern Hemisphere is almost always significantly larger than that in the Northern Hemisphere during the May storm.