Electron flow and visual aurora at the Harang discontinuity
We present several examples of the ionospheric electron drift patterns and of the aurora near the Harang discontinuity. The drift patterns were detected with the Scandinavian Twin Auroral Radar Experiment, and the auroral features were determined by using all-sky camera data. We find the behavior of the discontinuity to be strongly dependent on the level of magnetic activity as measured by the Kp index. During low activity the discontinuity remains at a fairly constant latitude for a considerable length of time. Usually, one to two auroral arcs are observed within the discontinuity. With increasing magnetic activity the Harang discontinuity tends to surge rapidly equatorward with mean speeds ranging from 150 to 600 m/s. This equatorward surge is observed at earlier local times as magnetic activity increases. We have found two cases in which an arc appears in the discontinuity at some point during its equatorward surge. The equatorward surge of the essentially east-west-aligned discontinuity appears to be associated with a limited region of strong equatorward electron flow which splits up into eastward and westward flow. This region may form the eastward termination of the discontinuity. The eastward termination of the Harang discontinuity during times of low magnetic activity appears to consist of an equatorward extension of the region of eastward electron flow within a spatially limited region near local magnetic midnight. We find the equatorward surges to be terminated by the sudden activation of an arc in the discontinuity, followed by a poleward expansion. Following these substorms the Harang discontinuity disappears from the field of view. At times, we have observed arcs to brighten and surge poleward in the region equatorward of the discontinuity. The discontinuity did not appear to be strongly affected by these substorms.
- Research Organization:
- Max-Planck-institut fuer Aeronomie, Katlenburg-Lindau, West Germany
- OSTI ID:
- 5755459
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 84:A8
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
AURORAE
HARANG DISCONTINUITY
PLASMA DRIFT
IONOSPHERE
LATITUDE EFFECT
RADAR
AURORAL OVAL
EARTH ATMOSPHERE
GEOGRAPHICAL VARIATIONS
MEASURING INSTRUMENTS
PLANETARY IONOSPHERES
RANGE FINDERS
VARIATIONS
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena