Ionospheric Signatures of Plasma Injections in the Cusp Triggered by Solar Wind
Pressure Pulses

J. Cerisier, A. Marchaudon, J. Bosqued, K. McWilliams, H. Frey, M. Bouhram, 
and M. Forster


During sporadic reconnection events (flux transfer events or FTEs) at the
dayside magnetopause, magnetosheath plasma enters the magnetosphere along cusp
field lines. It is expected that these enhanced parallel plasma flows occur in
conjunction with enhanced ionospheric convection events driven by the magnetic
tension at the reconnection site. Associated optical auroral emissions result
from enhanced precipitation of the magnetosheath plasma. If such events have
long been recognised as due to IMF variations, the triggering role of solar wind
pressure pulses is not definitely established. We analyse coordinated
observations made on July 14, 2001 simultaneously in the mid-altitude cusp by
Cluster and at the ionospheric magnetic footprint by SuperDARN and 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, convection flow channels are observed in the
ionosphere by the SuperDARN radars. Based on the spatial and temporal relation
between these various signatures, a description of the response of the dayside
magnetosphere to the pressure pulses is proposed. The main considerations
involved  in this description are: (1) the solar wind dynamic pressure pulses
are the drivers of plasma injections from the magnetosheath. (2) The ionospheric
convection bursts start shortly after the auroral intensifications and their
duration is much longer (10 min as against 4 to 6 min for the auroral
intensifications). (3) The convection bursts do not occur at the same latitude
as the precipitation, but on the poleward side of the cusp precipitation. (4)
Alfven waves are responsible of the transmission of the magnetic stress from the
reconnection site to the ionosphere where they are strongly attenuated by
reflection in the upper ionosphere. This set of observations demonstrates that
the convection bursts are a "fossil" signature  of the compression-injection
process as it is also the case for reconnection at the dayside magnetopause
driven by the IMF alone.

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Presentation, Fall A.G.U. Meeting, San Francisco, CA, 13-17 December 2004