Energetics of a substorm on 15 August, 2001: Comparing empirical methods and a global MHD simulation

Energy transferred from the solar wind into the magnetosphere–ionosphere system is dissipated largely through the occurrence of substorms. In this paper, a substorm that occurred on 15 August, 2001, between 0220 and 0620 UT is analyzed using several empirical estimates for energy input, for Joule heating and for electron precipitation. The total energy input is estimated in terms of Akasofu’s epsilon parameter, with original scaling parameter l0 = 7RE and revised scaling l0 = 10RE. Empirically estimated energy input is compared to the results of a GUMICS-4 global MHD simulation. Temporal variation of the input curves compare favorably during substorm growth and expansion phases, while there are differences during the substorm recovery phase. Global electron energy dissipation given by PIXIE on board the POLAR spacecraft matches nicely to the results of the GUMICS-4 simulation in temporal variations, but the absolute levels of dissipation are quite different.