Other
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm42b0602m&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM42B-0602
Other
2704 Auroral Phenomena (2407), 2716 Energetic Particles, Precipitating, 2736 Magnetosphere/Ionosphere Interactions, 2740 Magnetospheric Configuration And Dynamics, 2788 Storms And Substorms
Scientific paper
Latitudinal expansion of substorm auroras is explained by the poleward motion of the dipolarization region during the expansive phase. However the cause of the expansion of the aurora in local time is not fully understood and we used IMAGE FUV observations of 154 substorms to investigate it. Images of the Wideband Imaging Camera and the SI-12 proton auroral imager were re-projected to a rectangular magnetic latitude local time coordinate grid during 154 substorms. A representative function of the intensity distribution as a function of magnetic latitude, composed of two Gaussian peaks, was fitted to the projected images and the fitting parameters were obtained for all magnetic local times (MLT-s). This fitting permitted the effective removal of dayglow and other non auroral artifacts and yielded simple parameters to examine the properties of the aurora. The integrated intensity of the fitted double Gaussian functions were used to represent the intensity of the aurora at a particular MLT. Using this, intensity MLT-keograms were produced to examine the MLT development of the proton and electron aurora. These keograms show that the nightside aurora expands after substorm onset, but in addition to the expansion, the luminosity exhibits a bulk motion in the (MLT) direction towards dawn or dusk. No regular trends were derived in the direction or speed of the luminosity of the aurora in either the proton or the electron case. The MLT motion of the post substorm aurora therefore does not represent the drift motion of the injected particles in the magnetosphere but rather it represents a gradual drift of the particle injection source region. In previous case studies, comparison of energetic neutral atom (ENA) data with FUV showed that there is good agreement between lower energy trapped and precipitating fluxes. From our study therefore we propose that the substorm expansion in local time is a motion of the source of the particle injection during the process of the substorm.
Frey Harald U.
Mende Stephen B.
Morsony Brian J.
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