Unusual SuperDARN and EISCAT Doppler Shifts, Spectral Widths and Power Levels in Response to a Substorm-Like Change in Convection
J.-P. ST.-MAURICE(1), J.-P. VILLAIN (2), and W. KOFMAN (3)
(1) University of Western Ontario, Canada
(2) LPCE France
(3) LPG, France.
Following a sudden change in the solar wind properties that triggered a particle injection event, both the EISCAT radar and the Finland and Iceland East radars of the SuperDARN radar chain were making plasma observations of what seemed to be part of a substorm onset. The EISCAT radar was recording observations along the geomagnetic field at the time. About 10 min after the recorded changes in the solar wind properties, an unusual pattern of extremely powerful SuperDARN echoes started to be observed well north of the EISCAT radar position. This "cloud" of echoes was initially aligned rather well with the L shell geometry. At first it simply intensified and expanded in all directions before its eastern edge started to move south. Later still, the whole cloud was observed moving towards EISCAT and then westward. When the cloud finally moved well into its field of view, the Iceland East radar recorded a large and sudden jump in the Doppler shift of its echoes just across the cloud boundary. Also, just equatorward of the cloud, SuperDARN recorded unusually narrow spectra that did not match the ExB drift observed by the EISCAT radar. The disagreement with the EISCAT drifts was such that the SuperDARN reconstructed drifts were 90 degrees off the east-west drift direction recorded by EISCAT ionospheric drift observations. This disagreement lasted until the cloud of echoes passed just immediately north of EISCAT. At that point, EISCAT recorded a sizeable jump in the electric field and a sudden topside depletion. We conclude from all these observations that the cloud corresponded for whatever reason to a rather sizeable region of unusually strong enhancement in the convection electric field with the distinction of a very well defined, sharp, convection boundary. Near that boundary there might have been regions of intense parallel thermal electron drifts that were responsible for the non ExB drifting SuperDARN plasma echoes. It is not clear what role the cloud, with its 1 to 2 km/s speed, was playing in the global geophysical substorm onset context.
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