CUSP CLEFT AURORAL ACTIVITY IN RELATION TO SOLAR-WIND DYNAMIC PRESSURE, INTERPLANETARY MAGNETIC-FIELD B-Z AND B-Y/

Continuous optical observations of cusp/cleft auroral activities withi n approximate to 09-15 MLT and 70-76 degrees magnetic latitude are stu died in relation to changes in solar wind dynamic pressure and interpl anetary magnetic field (IMF) variability. The observed latitudinal mov ements of the cusp/cleft aurora in response to WIF B, changes may be e xplained as an effect of a variable magnetic field intensity in the ou ter dayside magnetosphere associated with the changing intensity of re gion 1 field-aligned currents and associated closure currents. Ground magnetic signatures related to such currents were observed in the pres ent case (January 10, 1993). Strong, isolated enhancements in solar wi nd dynamic pressure (Delta p/p greater than or equal to 0.5) gave rise to equatorward shifts of the cusp/cleft aurora, characteristic aurora l transients, and distinct ground magnetic signatures of enhanced conv ection at cleft latitudes. A sequence of auroral events of approximate to 5-10 min recurrence time, moving eastward along the poleward bound ary of the persistent cusp/cleft aurora in the approximate to 10-14 ML T sector, during negative WIF B, and B, conditions, were found to be c orrelated with brief pulses in solar wind dynamic pressure (0.1 < Delt a p/p < 0.5). Simultaneous photometer observations from Ny Alesund, Sv albard, and Danmarkshavn, Greenland, show that the events often appear ed on the prenoon side (approximate to 10-12 MLT), before moving into the postnoon sector in the case we study here, when IMF B-y < 0. In ot her cases, similar auroral event sequences have been observed to move westward in the prenoon sector, during intervals of positive B-y. Thus a strong prenoon/postnoon asymmetry of event occurence and motion pat tern related to the IMF B-y polarity is observed. We find that this ca tegory of auroral event sequence is stimulated bursts of electron prec ipitation that originate from magnetosheath plasma that has accessed t he dayside magnetosphere in the noon or near-noon sector, possibly at high latitudes, partly governed by the IMF orientation as well as by s olar wind dynamic pressure pulses.