EXTENDED PERIOD OF POLAR-CAP AURORAL DISPLAY - AURORAL DYNAMICS AND RELATION TO THE IMF AND THE IONOSPHERIC CONVECTION

An unusually extended period (5 h) of polar cap auroral display on 3 A ugust 1986 is examined. Auroras have been investigated using ground-ba sed data as well-as measurements from the IMP-8 space-craft in interpl anetary space and simultaneous observations from the polar-orbiting sa tellites Viking and DE-1 in the northern and southern hemispheres, res pectively. It is found that visible Sun-aligned arcs are located insid e the transpolar band of the theta-aurora observed from the satellite in ultraviolet wavelengths,The transpolar band can contain several Sun -aligned arcs that move inside the band toward the morning or-evening side of the auroral oval independent of the direction of the-band move ment. Intensifications of polar cap auroras With durations of up to ab out 30 min are observed. No change has been found in either IMF parame ters or substorm activity that can be related to these intensification s. The theta-aurora occurred during a 2-h period when the B-z-componen t of the IMF was negative. A tendency is noted for dawnward (duskward) displacement of the transpolar band when B-y > 0 (B-y < 0) in the sou thern hemisphere. Simultaneous observations of auroral ovals during in terplanetary B-z < 0, B-y < 0 and B-x > 0 in both hemispheres and conv ection patterns for B-z < 0 and B-y < 0 have been displayed using sate llite and ground-based measurements. It was found that the transpolar band of the theta-aurora in the sunlit hemisphere was situated in the region of large-scale downward Birkeland currents.