Energy content in the storm time ring current

Given the important role the ring current plays in magnetospheric energetic s, it is essential to understand its strength and evolution in disturbed ti mes. There are currently three main methods for deducing the strength of th e ring current: measuring ground magnetic perturbations, measuring high-alt itude magnetic perturbations, or directly measuring ring current particles. The use of ground magnetometers is the most convenient, and many use the g round magnetometer-derived Dst index as a proxy for the ring current. Recen t work suggests, however, that a substantial portion of Dst may not be caus ed only by the ring current but also by local induction effects or other ma gnetospheric currents, so simply using the Dst index may yield inaccurate r esults. This study uses direct particle measurements to calculate the stren gth of the ring current and compares this to the measured Dst values. We in vestigate several magnetic storm intervals, using the Polar Charge and Mass Magnetospheric Ion Composition Experiment (CAMMICE) to measure ring curren t 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 beha vior of the ring current compared to Dst as well as to compare the usefulne ss of the Dst proxy for different types of storms. Ring current ions are sh own in this analysis to contribute, on average, half of the Dst depression, with a large variation among individual events.