A SEARCH FOR LARGE-AMPLITUDE ELECTRIC FIELD STRUCTURES

USING CLUSTER MULTI-POINT OBSERVATIONS NEAR PERIGEE

G. T. Marklund (1), P.-A. Lindqvist (1), T. Karlsson (1), M. Andre (2), G.

Gustafsson (2)

(1): Alfven Laboratory, The Royal Institute of Technology, Stockholm; (2) Swedish

Institute of Space Physics, Uppsala

Large-amplitude electric fields have been observed on auroral field lines at altitudes

of a few Earth radii or more above the auroral ionosphere by a number of spacecraft

such as Dynamics Explorer 1, Viking and Polar. In many studies such observations

have been interpreted in terms of quasi-static field-aligned electric fields existing

below the spacecraft whereas recent Polar observations of large-amplitude electric

fields were interpreted as signatures of Alfvén waves carrying enough Poynting flux

to produce intense auroral arcs. Whether the energy transport between the

magnetosphere and the auroral ionosphere may be described by a quasi-static

current circuit or by an Alfvén wave scenario is a fundamental question which we

will adress in this study. Electric field data obtained near perigee where the four

spacecraft are aligned as pearls on a string are used for this study. The time

separation of about 10 minutes between consecutive passes of the four satellites

allows the temporal and spatial characteristics of the electric field structures

encountered to be investigated in great detail. First results of this study will be

presented and compared to results from crossings of auroral flux tubes at various

altitudes by other spacecraft.