Ionospheric signatures of plasma injections in the cusp triggered by solar wind pressure pulses.

We describe coordinated observations made on 14 July 2001 simultaneously in the midaltitude cusp by Cluster and at the cusp's ionospheric magnetic footprint by Super Dual Auroral Radar Network (SuperDARN) and Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) during a period of three successive solar wind dynamic pressure pulses. In association with each of these pulses, Cluster observes plasma injections while auroral images from the IMAGE spacecraft show enhanced precipitation in the cusp. Following these plasma injections, channels of fast convection flows are observed in the ionosphere by the SuperDARN radars. On the basis of the spatial and temporal relationships between these various signatures, we analyze the response of the dayside magnetosphere and ionosphere to the pressure pulses as follows: (1) the solar wind dynamic pressure pulses are the drivers of plasma injections from the magnetosheath into the cusp; (2) the ionospheric convection bursts start shortly after the auroral intensifications and their duration is much longer (10 min versus 4–6 min for the auroral intensifications); (3) the convection bursts occur on the poleward side of the cusp precipitation; and (4) the Alfvén waves that are responsible of the transmission of the magnetic stress from the reconnection site to the ionosphere are strongly reflected in the upper ionosphere. This, in addition to possible parallel potential drops, may explain the imperfect mapping of the magnetospheric electric field into the ionosphere during the injections. These observations demonstrate that the convection bursts are “fossil” signatures of the compression–injection process, which is also a signature of reconnection at the dayside magnetopause driven by the interplanetary magnetic field alone