Local variations of interplanetary magnetic field at Earth's bow shock

Abstract

We present interplanetary magnetic field (IMF) observations from Geotail and Wind in which the IMF was not uniform over spatial scales relevant to the magnetosphere. Geotail. at the dawn flank of the Earth's bow shock, measured magnetic field directions 60° to 120° different from the magnetic field measured by Wind on the duskside ∼30 RE upstream, during a 2‐hour interval. If there is a global connection between these observations, one possible explanation is a kink in the magnetic field near the Sun‐Earth line. The different orientations of IMF at Wind and Geotail (and thus the kink) change during the 2‐hour interval. Multiple shock crossings may have resulted from the changing orientations driving small surface waves on the shock surface. During this interval the bow shock does not fit a standard dawnside‐quasi‐parallel‐duskside‐quasi‐perpendicular picture. Instead, both sides of the bow shock may have been locally quasi‐perpendicular. The question of where a quasi‐parallel bow shock and/or foreshock could form needs to be explored. Both before and after the 2‐hour time interval, the IMF was close to uniform as measured by Wind. Geotail. and IMPS.