MULTISATELLITE OBSERVATIONS OF MESOSCALE ELEC-TROSTATIC

STRUCTURES IN THE OUTER CUSP

C. Cully (1,2), M. Andr´e (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 d’Etude Spatiale des Rayonnements, Toulouse, France, (5) Finnish

Meteorological Institute, Helsinki, Finland.

cully@phys.ucalgary.ca

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.