Characteristics of dipolarization onset time and location at geosynchronous orbit during auroral substorm onset

Details Characteristics of dipolarization onset time and location at geosynchronous orbit during auroral substorm onset Characteristics of dipolarization onset time and location at geosynchronous orbit during auroral substorm onset

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm52a06l&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SM52A-06

Physics

2704 Auroral Phenomena (2407), 2740 Magnetospheric Configuration And Dynamics, 2788 Storms And Substorms

Scientific paper

Magnetotail stretching prior to onset constitutes the substorm growth phase morphology. After some time the stretched field lines relax and ``snap'' back from a taillike to a dipolelike configuration, signifying the onset of substorm. In this paper we investigate the timing and spatial extent of the dipolarization seen at geosynchronous orbit relative to auroral breakup. Data used are the magnetic field observations from GOES 8 and GOES 9 and the global auroral observations from the Polar ultraviolet imager. We survey a year (1997) worth of data and obtain 32 unambiguous dipolarization onsets that occurred within 2 hours of magnetic local time from their associated auroral breakup locations. The average time difference between the two onset signatures was 1.7 min with the auroral breakup leading the dipolarization onset. The delay of the dipolarization onset with respect to the auroral breakup is found to be associated with the longitudinal expansion of the auroral bulge. We also show for the first time that the longitudinal extent of dipolarization, as mapped to the ionosphere along the magnetic field, is approximately consistent with the longitudinal extent of the substorm auroral bulge. Statistical results indicate that geosynchronous dipolarization onset occurs ~1 min prior to auroral breakup when the observation is taken at ~0.5 hour in magnetic local time eastward of the eastern edge of the auroral bulge, consistent with the concept of substorm current wedge.

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