Configurations of the Quiet Polar Cap and Its Response to a Sudden Increase of the Energy Input Rate Epsilon

摘要

Following a geomagnetically quiet period of 17 hr duration a sudden increase of the solar wind-magnetosphere energy coupling function epsilon to greater than 100 billion W occurred at 0510 UT on Nov. 29, 1984, and a moderate substorm onset was observed in the midnight sector of the auroral oval at 0612 UT. The shape and position of the boundary of the polar cap during quiet conditions, and the influence of the sudden disturbance on the boundary position were studied. It is concluded that an equatorward shift of the polar cap boundary caused by an increase in epsilon may be observed at part of the boundary earlier than the corresponding shift of the auroral oval. The shift may take place at different hours in different sectors of the polar cap with time differences of at least 20 min between dawn and dusk.