Solar sources of interplanetary southward <i>B_z</i> events responsible for major magnetic storms (1978‐1979)

Abstract

Tsurutani et al. [1988] analyzed the 10 intense interplanetary southward B z events that led to major magnetic storms ( Dst &lt;−100 nT) during the 500‐day interval, August 16, 1978, through December 28, 1979. In this paper we report solar sources of the major storms and discuss their interplanetary effects. Seven of the sources of the 10 major storms are flares and 3 are prominence eruptions. The ratio is consistent with frequency of these two types of events occurring on the Sun during this period. The flares range from M1 to X2 in peak soft X ray emissions. However, the largest of the 10 storms ( Dst = −220 nT) as well as the two strongest shocks ( M &gt;3.0) are associated with prominence eruptions. For three of the five southward B z events in which the driver gases are the causes of the intense southward field leading to magnetic storms, the photospheric fields of the solar sources have no dominant southward component, indicating the driver gas fields do not always result from a simple outward convection of solar magnetic fields. Finally we compare the solar events and their resulting interplanetary shocks and find that the standard solar parameters do not correlate with the strengths of the resulting shocks at 1 AU. The implications are discussed.