Dynamics of Variable Dusk-Dawn Flow Associated with Magnetotail Current Sheet Flapping

Abstract:

We present Cluster spacecraft observations from 12^th October 2006 of earthward convective magnetotail plasma flows. During a 4-minute interval, the azimuthal (v_⊥y) component of the flows was observed to vary between dawnward and duskward. Combined observations of the upstream solar wind conditions from OMNI, and ionospheric convection data using SuperDARN, indicate a large-scale magnetospheric morphology consistent with positive IMF B_y penetration into the magnetotail. The dusk-dawn sense of the localised convective flows observed by Cluster disagrees with expectations based on current theories of Interplanetary Magnetic Field (IMF) B_y control of magnetotail asymmetries. Inspection of the in-situ Cluster magnetic field data reveals a flapping of the magnetotail current sheet and the presence of a localised B_y negative kink at the location of Cluster 1. Results from the curlometer analysis technique suggest that the dusk-dawn flow perturbations were being driven by the J x B force associated with the current sheet flapping. The direction of the flows seems consistent with removal of the localised B_y-negative kink from an otherwise globally B_y-positive twisted tail.