Energy content in the storm time ring current

Abstract

Given the important role the ring current plays in magnetospheric energetics, it is essential to understand its strength and evolution in disturbed times. There are currently three main methods for deducing the strength of the ring current: measuring ground magnetic perturbations, measuring high-altitude magnetic perturbations, or directly measuring ring current particles. The use of ground magnetometers is the most convenient, and many use the ground magnetometer-derived Dst index as a proxy for the ring current. Recent work suggests, however, that a substantial portion of Dst may not be caused only by the ring current but also by local induction effects or other magnetospheric currents, so simply using the Dst index may yield inaccurate results. This study uses direct particle measurements to calculate the strength of the ring current and compares this to the measured Dst values. We investigate several magnetic storm intervals, using the Polar Charge and Mass Magnetospheric Ion Composition Experiment (CAMMICE) to measure ring current ions. We then use the Dessler-Parker-Sckopke relation to compare this to the measured Dst. This analysis is used both to understand the general behavior of the ring current compared to Dst as well as to compare the usefulness of the Dst proxy for different types of storms. Ring current ions are shown in this analysis to contribute, on average, half of the Dst depression, with a large variation among individual events. Copyright 2001 by the American Geophysical Union.