MULTISATELLITE OBSERVATIONS OF MESOSCALE ELEC-TROSTATIC
STRUCTURES IN THE OUTER CUSP
C. Cully (1,2), M. AndrŽe (2), T. Carozzi (2), A. Pedersen (3), B. Jackel (1),
F. Pitout (2,4), E. Donovan (1), H. Opgenoorth (2,5) and H. R`eme (4)
(1) Institute for Space Research, University of Calgary, Canada, (2) Swedish
Institute of Space Physics, Uppsala, Sweden, (3) University of Oslo, Norway,
(4) Centre dEtude Spatiale des Rayonnements, Toulouse, France, (5) Finnish
Meteorological Institute, Helsinki, Finland.
Characterisation of electric fields present in the high-altitude cusp regions has
traditionally been hampered by difficulties involved in the separation of small-scale
spatial changes from rapid temporal changes when using a single satellite.
The initial months of Cluster operation have provided the first simultaneous
multisatellite electric field measurements in this region, with a spacecraft sepa-ration
of roughly 500 km. Using data from all four satellites, it is now possible
to examine quasi-static electric field structures with scale lengths on the order
of the spacecraft separation and larger, and with resolution of the spatial and
temporal components. Particular attention is paid to the vorticity of the elec-tric
field, a parameter that has previously been impossible to directly observe.
Solar wind conditions as well as data from the EISCAT ESR radar facility
are used to help characterise the macroscale activity present during the cusp
crossings, so as to establish the larger context in which the observations were
made. Implications for ion transport through these structures are discussed.