Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsm44b..01g&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM44B-01
Physics
2721 Field-Aligned Currents And Current Systems (2409), 2790 Substorms
Scientific paper
We present a large statistical study of the spatial and temporal morphology of the ground magnetic field perturbations during classical bulge-type auroral substorms. Images obtained by the Polar VIS Earth camera with superimposed magnetic perturbation vectors from all available ground based magnetometers (>100) are utilized in the study of 119 carefully selected events. To reduce smearing of the key emission features and perturbation patterns due to the variations of the local times of onsets and rates of expansion and recovery, we normalize substorm time and positions of the western and eastern ends of the bulge region to an average substorm. Our empirical time dependent model of the ground magnetic field perturbations displays a number of interesting features. The magnetic perturbations are clearly organized into two different latitude and local time bands: 1) a primarily pre-midnight band near the poleward edge of the bulge and moving poleward with the UV emissions; 2) a slightly pre-midnight to post-midnight/midnight band that stays fixed in latitude. These can overlap in local time and latitude and vary in relative strength and position from event to event. Sub-auroral magnetic perturbations are used to indicate the locations of the feeding and drainage of the auroral electrojet system. We interpret the first region as the classical substorm current wedge and the second as the region known as the directly driven current but present evidence that the cause is more like internal to the magnetosphere. To what extend these current systems are coupled around midnight cannot yet be determined.
Frank Loya
Gjerloev Jesper
Hoffman Robert
Sigwarth J.
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