Spatiotemporal features of the auroral acceleration region as observed by Cluster

Abstract

A pair of negative electric potential structures associated with inverted-V aurora is investigated using electric and magnetic field, ion and electron data from the Cluster spacecraft, crossing the auroral acceleration region (AAR) at different altitudes above the Northern hemisphere midnight auroral oval. The spatial and temporal development of the acceleration structures is studied, given the magnetic conjunction opportunity and the one minute difference between the Cluster spacecraft crossings. The configuration allowed for estimation of characteristic times of development for the two structures and of the parallel electric field and potential drop for the more stable one. The first potential structure had a width of ∼80 km (projected to the ionosphere) and was relatively short-lived, developing in less than 40 s and decaying in one minute. The parallel potential drop increased between altitudes of 1.13 RE and 1.3 RE, whereas the acceleration potential above 1.3 R E remained almost unchanged during that time. This intensification occurred mainly after the time when the associated upward current had reached its maximum value. The second structure had a width of ∼50 km and was subject to an increase by a factor of 3 of the parallel potential drop below 1.3 RE, during about 40 s, after which it remained rather stable for one minute or more. Similarly here, the acceleration potential above 1.3 R E remained roughly unchanged. For the more stable second structure, an average parallel electric field between 1.13 and 1.3 RE could be estimated (∼0.56 mV/m). The conductance along the flux tube was also stable for one minute or more. Copyright 2011 by the American Geophysical Union.