There are important geomagnetic implications whenever the interplanetary magnetic field (IMF) turns northward or southward. This paper addresses only the initial turning when the solar events' shock signals first reach 1 AU. A three-dimensional (3D), time-dependent, MHD model [Han et al., 1988] of disturbances' propagation through the solar wind and interplanetary magnetic field (IMF) has been used by Wu (1993) to develop a ''recipe'' for the initial north- or south-turning of the IMF's polarity. Its temporal behavior thereafter is not addressed in this paper. Four independent data sets have been used [Wu et al., 1996a, b, c] in a study currently underway to test this idea. A fifth data set [Gosling et al., 1990] is used in this paper to examine, via this idea, the initial B-z polarity's change at 1 AU caused by shocks associated with interplanetary/coronal mass ejection events and large geomagnetic storms during the period of August 1978 to October 1982. Twenty-five events from this fifth data set are studied; the prediction model is in agreement with twenty-one of them. Our results suggest that the initial IMF B-z polarity's change at 1 AU may be associated with a simple relationship between the location of the solar disturbance, the relative position of the heliospheric current sheet, and the initial toward or away; polarity of the IMF at Earth.
