ABSTRACT
An interplanetary shock can abruptly compress the magnetosphere, excite magnetospheric waves and field-aligned currents, and cause a ground magnetic response known as a sudden commencement (SC). However, the transient (<â¼1 min) response of the ionosphere-thermosphere system during an SC has been little studied due to limited temporal resolution in previous investigations. Here, we report observations of a global reversal of ionospheric vertical plasma motion during an SC on 24 October 2011 using â¼6 s resolution Super Dual Auroral Radar Network ground scatter data. The dayside ionosphere suddenly moved downward during the magnetospheric compression due to the SC, lasting for only â¼1 min before moving upward. By contrast, the post-midnight ionosphere briefly moved upward then moved downward during the SC. Simulations with a coupled geospace model suggest that the reversed E â × B â vertical drift is caused by a global reversal of ionospheric zonal electric field induced by magnetospheric compression during the SC.
