Structure of field-aligned currents in the polar cusp: conjugated observations by Cluster, Double Star-2 and SuperDARN
Résumé
Dayside field-aligned currents flowing along highly conductive field lines transmit magnetic stress caused by magnetopause reconnection, to the magnetosphere and the conjugated ionosphere. On 20 February 2005, Cluster at high altitude and Double Star-2 (TC-2) at mid altitude are situated in the vicinity of the northern cusp / mantle, with Cluster moving sunward and TC-2 anti-sunward. Their magnetic footprints come very close together at about 15:45 UT, just over the common field-of-view of SuperDARN radars. Based on this conjunction, we compare the transverse structure (form/elongation) of field-aligned current tubes at different altitudes, their intensity, their temporal dynamics, the associated particle carriers and their closure in the ionosphere. Cluster field-aligned currents are determined from the multi-satellite curlometer technique and compared to the currents determined from the single-satellite method based on the infinite current sheet hypothesis. This last method is also used to calculate currents from TC-2 magnetic data. The good comparison between drift velocity of injections calculated from the four-spacecraft timing technique and convection field measured by SuperDARN, allows to take into account the drift of the injection structures in the current calculation. Finally, fieldaligned currents deduced from magnetic measurements are also compared with electron and ion fluxes measured onboard Cluster and TC-2.