THE GEOSPACE ENVIRONMENT MODELING GRAND CHALLENGE - RESULTS FROM A GLOBAL GEOSPACE CIRCULATION MODEL

We have used our Global Geospace Circulation Model (GGCM) to simulate two time intervals that were proposed as the Geospace Environment Mode ling (GEM) Grand Challenge for modelers to investigate to what extent and accuracy models can predict the ionosphere's response to the solar wind and interplanetary magnetic field. In this paper we present comp arisons of our GGCM with the comprehensive experimental study by Lyons [this issue] (which provided synoptic maps of the polar cap electrody namics and particle precipitation) for the two time intervals, January 27, 1992, 1325-1715 UT and 1730-1930 UT. We find a very good agreemen t between the potential patterns predicted by our model and those obta ined by the assimilative mapping of ionospheric electrodynamics (AMIE) procedure. We also find that the separatrix and cusp locations predic ted by our model generally compare well with those obtained from parti cle precipitation data. The soft electron zone of ionospheric precipit ation, as defined by Lyons, lies almost entirely in the region for whi ch our model predicts open field lines. However, the model predicts cr oss polar cap potential drops that are roughly a factor of 2 larger th an those predicted by AMIE.