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Ann. Geophys., 16, 1322-1331, 1998
www.ann-geophys.net/16/1322/1998/
© European Geosciences Union 1998
Velocity of auroral arcs drifting equatorward from the polar cap
P. J. S. Williams, C. F. del Pozo, I. Hiscock, and R. Fallows
Adran Ffiseg, Prifysgol Cymru Aberystwyth, Ceredigion SY23 3BZ, Wales, UK e-mail: pjw@ aber.ac.uk
Abstract. The drift velocity of an auroral arc is
compared with the component of F-region plasma velocity in the same direction
for ten cases where the arc is seen to move steadily equatorward for several
minutes without any major change in appearance or orientation. In most cases the
two velocities are close, but on two occasions the drift velocity of the arc is
much higher than the plasma velocity. From the cases studied it appears that
during the growth and recovery phase of the substorm cycle the arc moves with a
velocity close to the convection velocity, but during the expansion phase this
is not the case.
Key words. Magnetospheric physics (auroral phenomena;
electric fields; plasma convection)
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