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Ann. Geophys., 22, 1649-1664, 2004
www.ann-geophys.net/22/1649/2004/
© European Geosciences Union 2004
Meridional motions of the afternoon radar aurora, auroral electrojets, and absorption patches under variable IMF conditions
R. A. Makarevitch1, F. Honary2, A. V. Koustov3, and M. V. Uspensky3,4
1Department of Communication Systems, Lancaster University, Lancaster, LA1 4YR, UK
2Institute of Space and Atmospheric Studies, University of Saskatchewan, 116 Science Place, Saskatoon, SK, S7N 5E2, Canada
3Finnish Meteorological Institute, Geophysical Research Division, P. O. Box 503, Helsinki, FIN-00101, Finland
4on leave from Murmansk State Technical University, Sportivnaya 13, Murmansk, 183010, Russia
Abstract. The meridional motions of the CUTLASS HF and STARE VHF coherent
echoes, IMAGE equivalent electrojet currents, and IRIS absorption
patches during the postnoon/early-evening event of 14
February 2000 are presented. The motions were found to be
synchronous, to a first approximation, for all instruments. The
temporal correlation between motions in the radar and magnetometer
data was exceptionally good, although spatially the areas with the
E-region backscatter and most intense equivalent currents were not
coincident, with the HF (VHF) echoes being shifted 100–200km
(20–50km) equatorward (poleward). The meridional motions of the
radar echoes and electrojet currents appeared to be controlled by
the IMF Bz changes; the meridional propagation direction was
equatorward (poleward) during the intervals when the IMF was
southward (northward), with one exception when the poleward
progression continued after the IMF southward turning. We relate
the observed meridional motion patterns to the polar cap
expansion/contraction during variable IMF conditions and discuss
the relative importance of two types of processes: the dayside
reconnection and IMF-triggered substorms. We also investigate the
irregularity Doppler velocity for the STARE (144MHz) and CUTLASS
(12MHz) observations at large flow angles in the context of the
eastward and westward electrojet systems. We show that the 144-MHz
Doppler velocity is determined by a combination of two factors:
the sense of electrojet currents and the aspect angle conditions
within the STARE field of view. Finally, the behavior of small
dayside enhancements of the IRIS absorption (up to 0.5dB at 38.2MHz)
accompanying the radar echoes and electrojet currents is
examined. Since the velocity of the meridional displacements was
close to that of the poleward/equatorward progressing intense
currents, it is suggested that the absorption patches observed
during the event were related to the heating of the E-region
plasma by the unstable plasma waves in the regions of enhanced
electric fields.
Key words. Ionosphere (auroral ionosphere; electric fields
and currents; plasma convection)
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