Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm51b1294h&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SM51B-1294
Other
2704 Auroral Phenomena (2407), 2712 Electric Fields (2411), 2716 Energetic Particles: Precipitating, 2721 Field-Aligned Currents And Current Systems (2409)
Scientific paper
FAST electric field data and ion drift moments are combined to allow full DC E field studies of auroral return current regions. Statistical comparison of 71 return current potential structures showed several differences between linearly structured perpendicular E field events, where the ratio of the two E field components remains constant during the spacecraft crossing, and curved structures where the ratio varies. Linear structures can be interpreted as straight arcs, but curved structures require gradients in another dimension. We define a parameter eta, which is a comparison of the potential at the spacecraft and the upgoing electron characteristic energy. eta implies how much ionospheric fields which map up from the lower ionosphere are overlapped on typical U-shaped potentials. The influence of ionospheric fields on return current potential structures has been seen in previous numerical predictions. From our parameter study, it is found that ionospheric effects are dominant in linear structures and U-shaped potential models are mostly consistent with curved events. This result implies that the divergent electric fields of the downward current region seen by FAST are caused by both ionospheric fields and by U-shaped potentials. The spatial structure of the events, as indicated by the ratio of the E field components, allows us to distinguish them. Statistical studies of scale sizes, magnitudes of electric fields and magnetic perturbations and downward current density, sorted by the parameter eta, reveal various interesting features. We attempt to explain these properties on the basis of different potential models for linear and curved structures, which have important implications for models of the formation and evolution of potential structures for downward current regions.
Bonnell J. W.
Carlson Carl W.
Hwang Kyuwan
Lynch Kristina Anne
Peria W. J.
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