Classification and mean behavior of magnetic storms

TLDR

The study uses the Dst minimum as a common reference epoch, differing from the earlier Sugiura and Chapman 1960 approach. Dst index data from 1957–1993 were used to identify over 1,000 storms, classify them into five intensity categories based on minimum Dst, and compute the mean time variation for each class. The analysis shows that using Dst minimum yields better agreement between average and typical storm behavior, that peak ap and AE activity precede Dst minimum by 1–2 h, and that both sudden and gradual commencement storms are linked to a distinct drop in the interplanetary Bz component.

Abstract

The Dst index is used to identify more than 1000 storms which occurred in the time interval 1957 to 1993. Using the minimum Dst value as an indicator, we classify the storms as weak (482), moderate (346), strong (206), severe (45), and great (6). For each of these classes the mean time variation is determined. In contrast to the well‐known study of Sugiura and Chapman [1960], the Dst minimum is used as a common reference epoch. This leads to much better agreement between the average and the typical storm behavior. We also find that the maximum ap and AE activity precedes the Dst minimum by 1 to 2 hours. Finally, we demonstrate that both sudden commencement and gradual commencement storms are associated with a distinct decrease in the B z component of the interplanetary magnetic field.