THE JANUARY 10, 1997 AURORAL HOT-SPOT, HORSESHOE AURORA AND FIRST SUBSTORM - A CME LOOP

The January 10, 1997 interplanetary high-speed stream and the resultan t first substorm (similar to 0332 to 0334 UT onset) is studied. A 47 m inute interval of relatively intense southward interplanetary magnetic field (IMF) (B-S = 4 to 8 nT)bounded by two tangential discontinuitie s (TDs) is identified between the interplanetary shock and the magneti c cloud. The two discontinuities arrive at the magnetopause at similar to 0219 and similar to 0302 UT. The IMF B-S event served primarily to transfer solar wind energy to the magnetosphere/magnetotail, as no su bstorm expansion phase occurred during the event. The eventual energy release was in the form of a large substorm expansion phase which occu rred after (similar to 15-17 min.) a second IMF northward turning (aft er the end of the B-S interval). The interplanetary B-S event came aft er a prolonged northward IMF interval. During the initial part of the B-S event, both polar cap Sun- Earth aligned arcs formed (part of a th eta aurora) and an auroral hot spot along the main are took place. Lat er, during the B-S interval, an aurora in the shape of a horseshoe dev eloped at lower (60 degrees) latitudes (an oval with a gap in the noon sector). The dawnside portion of the horseshoe aurora became much bri ghter than the duskside with increasing time. The dawnside polar cap b oundary layer (PCBL) broadband waves were well correlated with low ene rgy ion fluxes (H+ He++, O+) during the event. It is speculated that t his IMF B-S structure may be an outer loop of the CME coming from the Sun. Another similar loop is identified just adjacent to the cloud.