Effects of substorms on the stormtime ring current index &amp;lt;i&amp;gt;Dst&amp;lt;/i&amp;gt;

G Rostoker

doi:10.1007/s00585-000-1390-2

Abstract

Abstract. There has been some discussion in recent times regarding whether or not substorm expansive phase activity plays any role of importance in the formation of the stormtime ring current. I explore this question using the Kp index as a proxy for substorm expansive phase activity and the Dst index as a proxy for symmetric ring current strength. I find that increases in Dst are mildly related to the strength of substorm expansive phase activity during the development of the storm main phase. More surprisingly, I find that the strength of Dst during the storm recovery phase is positively correlated with the strength of substorm expansive phase activity. This result has an important bearing on the question of how much the Dst index reflects activity other than that of the stormtime symmetric ring current strength for which it is supposed to be a proxy.Key words: Ionosphere (electric fields and currents) - Magnetospheric physics (current systems; storms and substorms)

Highlights

It has been known for some time that the negative Hcomponent depressions of up to several hundred nT observed at low-latitude magnetic observatories are due to large-scale currentsowing around the Earth carried by gradient/curvature drifting charged particles (Singer, 1957)
This research was started with the aim of trying to see if there was any clear relationship between substorm expansive phase (EP) activity and the development of the symmetric ring current
There is a clear tendency for Dst to increase with increasing Kp, which is not what one might have expected for recovery phase conditions imagine a situation in which changes in Dst and Kp seem to be correlated and yet an increase in symmetric ring current may not be attributable to the eects of substorm EP activity

Summary

Introduction

It has been known for some time that the negative Hcomponent depressions of up to several hundred nT observed at low-latitude magnetic observatories are due to large-scale currentsowing around the Earth carried by gradient/curvature drifting charged particles (Singer, 1957). These negative H-component storm disturbances can last for several days and comprise a main phase of up to several hours during which the disturbance strengthens and a recovery phase of up to many days during which the disturbance returns to its pre-storm level. The question has come into focus more recently through the contention of Iyemori and Rao (1996) that

Rostoker

Processing of the data and presentation format

Presentation of the data

Discussion of the results

Conclusions