Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002sgop..........k&link_type=abstract
Sodankyla Geophysical Observatory Publications
Astronomy and Astrophysics
Astronomy
Solar Wind, Solar Terrestrial Interactions, Earth Magnetosphere, Magnetic Disturbances, Auroral Arcs, Radar Astronomy, Polar Regions, Astronomical Models, Magnetic Fields, Visual Observation, Magnetohydrodynamic Flow
Scientific paper
Optical auroral observations combined with radar measurements were interpreted in terms of the source mechanisms of the magnetospheric convection and field-aligned currents and physical mechanisms of the auroral arcs. Relative motion of nightside auroral arcs with respect to the ambient plasma has shown that variations in the arc velocity lag behind corresponding variations in the ionospheric plasma drift velocity by 5 - 9 minutes. These observations indicate that the dawn-dusk electric potential difference arises at the open polar cap magnetic field lines due to the solar wind - magnetosphere interaction and then propagates to the closed magnetotail field lines through the ionosphere. A new type of noon poleward moving high-latitude auroral arcs (PMAA) was described, which shows essential differences from well-known PMAFs associated with reconnection and FTEs. The arcs arise at the closed magnetic field lines, are associated with strong convection disturbances, and propagate poleward at the velocity, which does not show any dependence on the ionospheric plasma convection along the same direction. We suggest that the field line resonance model is most promising to explain the origin of the PMAA. In the post-noon auroral ionosphere, a characteristic picture of spatial variations across the auroral oval is obtained for the horizontal and vertical plasma flows, field-aligned currents, and height profiles of the ionospheric plasma parameters (density and temperatures). Response of the postnoon high-latitude magnetosphere to the IMF changes has shown that: (1) Southward turnings of the interplanetary magnetic field were associated with bright afternoon auroral oval moving equatorward. The equatorward motion started 27 +/- 7 min after the IMF Bz turned southward at the subsolar point; (2) The IMF Bz northward deflection was followed by a decrease in both field-aligned current intensity and auroral luminosity. The decrease in the auroral luminosity lags behind the field-aligned current decrease by about 12 min; (3) In response to the IMF By turning from positive to negative values, maximum of the auroral luminosity does not change its position, whereas the convection reversal moves considerably. This observation allows us io suggest that the IMF By-related electric field can penetrate into the closed magnetosphere and produce convection changes in the region of the postnoon auroral oval.
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