Drifts of auroral structures and their relationship to geomagnetic activity

概要

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Accurate motion of some auroral structures, such as pulsating and non-pulsating patches and discrete auroral arc fragments is studied on the basis of all-sky TV observations of auroras. It is shown that the general drift pattern of these auroral structures correspond, on a gross scale, to magnetospheric convection, namely westward in the evening sector and eastward in the morning sector. The drift velocity ranges from 50 to 2000m/s, corresponding to the electric field intensity from 3 to 120mV/m at the ionospheric level and from 0.1 to 4mV/m in the magnetospheric equatorial region at an L value of about 6.5. The general drift pattern locally fluctuates, when new magnetic (and auroral) activities occur. Temporal and spatial changes in the drift of the patches are related to the evolution of a substorm. Clear enhancement in the drift velocity associated with increase in the westward electrojet is observed at a different local time region from the center of the electrojet. These results indicate that the convection electric field temporarily and spatially changes when a new substorm expansion of aurora occurs in the midnight sector.