Relations between the interplanetary magnetic field Bz, AE index, and cusp latitude

The connection between the interplanetary magnetic field (IMF) B z , AE index, and magnetospheric cusp location is examined qualitatively. Seven months during 1979–1980 were searched for periods of low auroral activity and/or periods when the IMF B z component and the AE index varied inconsistently (i.e., southward B z and quiescent AE ). During quiet auroral conditions, the IMF B z , AE index, and equatorward cusp boundary generally tend to act coherently, although during very quiet times the cusp may exhibit considerable variability that is apparently unassociated with either B z or AE . We found a number of instances in which the cusp location clearly followed B z more closely than AE , especially when a time delay of ≤ 1 hour was assumed. However, we cannot conclude that either B z or AE exerts a dominant influence on the latitudinal position of the polar cusp. The effects of B z and AE variations on the cusp are quite complicated and the observations simply do not indicate clear cusp response to one or the other. The largest equatorward cusp motions seem to occur as a result of prolonged southward B z lasting 3 hours or more, and cusp latitude appears to depend strongly on time‐accumulated B z .