Comparison of assimilative mapping and source surface model results for magnetospheric events of January 27 to 28, 1992

Abstract

We calculate polar cap boundaries and polar cap equipotentials obtained by using two modifications of the source surface model (SSM) for three intervals specified by the Geospace Environment Modeling (GEM) grand challenge and compare with results from the assimilative mapping of ionospheric electrodynamics (AMIE) code. In the first modification Birkeland currents are self‐consistently added to the SSM. In the second modification the magnetotail radius is increased, and the lobe magnetic field is modified to obtain a more realistic magnetotail. Both modifications of the SSM, although simple, are found to reproduce many of the features seen in the AMIE results. These include a duskward (dawnward) shift of the separatrix in the northern (southern) hemisphere because of negative IMF B y effects, and a good agreement for southern hemisphere equipotentials and for the locations or the nightside separatrix between open and closed field lines. However, both versions of our model give northern hemisphere separatrices that are more nearly circular than those observed and show IMF B y effects not present in the AMIE results; they also displace the dayside separatrix poleward of the positions indicated by observations.