On the asymmetric development of magnetic storm fields in low and middle latitudes

By a detailed analysis of the disturbance field of certain magnetic storms, including that of 13 September 1957, it is shown that there must be a fairly steady current system, partly external and partly ionospheric, which contributes a substantial portion of the asymmetry in the low and middle latitude storm field, independent of the growth and decay of auroral electrojets. A new model electric current system is presented to account for such an asymmetry. It is suggested that there is a gap in the ring current belt on the night side, and that the ring current is closed through the ionosphere.