Paper#: 129
Poster #:
Session Name: Workshop 5A: Tail Processes
Room: West Ballroom
Day: Wednesday
Time: 11:15-11:40 a.m.
Abstract Title: Cluster Observations of the Postmidnight Tail Current at 18 Re during Substorms
PresentSurname: McPherron, R.L.
All Authors: R.L. McPherron , M.G. Kivelson , K. Khurana, A. Balogh, et al.
Abstract : On August 15, 2001 the Cluster spacecraft passed through the plasma sheet at 0100 lt and distance 18 Re. During the passage three substorms were observed. Each substorm was characterized by dipolarization of Bz. The first and last substorms were also accompanied by strong earthward flows. We utilize a variety of ground and spacecraft observations to establish the circumstances of these correlated changes. For the entire interval the IMF By was strongly positive. For the first two substorms Bz was negative prior to the onset, but the third substorm occurred during northward field. The Cluster field data indicate that IMF By had rotated the tail current at 18 Re. In two substorms the arrival of the flow was associated with an intensification of an existing substorm expansion. The first substorm provides a clear example of a steep front of thickening of the plasma sheet passing over the spacecraft followed by several vertical oscillations in thickness. The third substorm took place while the spacecraft were very near the neutral sheet. It began with a very sharp negative perturbation in Bz followed by a brief burst of tailward flow. The usual signatures of dipolarization follow these effects. This dipolarization occurs in a step-wise manner with each field increment accompanied by a burst of earthward flow. We utilize the four spacecraft to calculate the curl in B and hence the total electric current. We will compare these current observations to simple models of the distribution of current in the plasma sheet.