Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm

Grocott, A. and Cowley, S.W.H. and Sigwarth, J.B. and Watermann, J.F. and Yeoman, T.K. (2002) Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm. Annales Geophysicae, 20 (10). pp. 1577-1601. ISSN 0992-7689

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Abstract

We present SuperDARN radar observations of the ionospheric flow during a well-observed high-latitude substorm which occurred during steady northward IMF conditions on 2 December 1999. These data clearly demonstrate the excitation of large-scale flow associated with the substorm expansion phase, with enhanced equatorward flows being observed in the pre-midnight local time sector of the expansion phase auroral bulge and westward electrojet, and enhanced return sunward flows being present at local times on either side, extending into the dayside sector. The flow pattern excited was thus of twin-vortex form, with foci located at either end of the substorm auroral bulge, as imaged by the Polar VIS UV imager. Estimated total transpolar voltages were ~40 kV prior to expansion phase onset, grew to ~80 kV over a ~15 min interval during the expansion phase, and then decayed to ~35 kV over ~10 min during recovery. The excitation of the large-scale flow pattern resulted in the development of magnetic disturbances which extended well outside of the region directly disturbed by the substorm, depending upon the change in the flow and the local ionospheric conductivity. It is estimated that the nightside reconnection rate averaged over the 24-min interval of the substorm was ~65– 75 kV, compared with continuing dayside reconnection rates of ~30–45 kV. The net closure of open flux during the sub-storm was thus ~0.4–0.6 × 108 Wb, representing ~15–20% of the open flux present at onset, and corresponding to an overall contraction of the open-closed field line boundary by ~1° latitude.

Item Type:
Journal Article
Journal or Publication Title:
Annales Geophysicae
Additional Information:
c European Geosciences Union 2002
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/1900/1912
Subjects:
?? IONOSPHERE (AURORAL IONOSPHERE; IONOSPHERE-MAGNETOSPHERE INTERACTIONS; PLASMA CONVECTION)EARTH AND PLANETARY SCIENCES (MISCELLANEOUS)ASTRONOMY AND ASTROPHYSICSATMOSPHERIC SCIENCEGEOLOGYSPACE AND PLANETARY SCIENCE ??
ID Code:
35421
Deposited By:
Deposited On:
18 Jan 2011 13:05
Refereed?:
Yes
Published?:
Published
Last Modified:
16 Sep 2023 00:27