Space Technology 5 multipoint observations of temporal and spatialvariability of field-aligned currents

摘要

Space Technology 5 (ST5) is a constellation mission consisting of threemicrosatellites. It provides the first multipoint magnetic field measurements in low Earthorbit, which enables us to separate spatial and temporal variations. In this paper, wepresent a study of the temporal variability of field-aligned currents using the ST5 data. Weexamine the field-aligned current observations during and after a geomagnetic storm andcompare the magnetic field profiles at the three spacecraft. The multipoint datademonstrate that mesoscale current structures, commonly embedded within large-scalecurrent sheets, are very dynamic with highly variable current density and/or polarity in,-10 min time scales. On the other hand, the data also show that the time scales forthe currents to be relatively stable are ,1 min for mesoscale currents and —10 min forlarge-scale currents. These temporal features are very likely associated with dynamicvariations of their charge carriers (mainly electrons) as they respond to the variations ofthe parallel electric field in auroral acceleration region. The characteristic time scalesfor the temporal variability of mesoscale field-aligned currents are found to be consistentwith those of auroral parallel electric field.