Dynamics of the Equatorward Boundary of the Auroral Oval

摘要

The Auroral Boundary Index determined on the basis of DMSP precipitating electron data is used to examine the expansion and contraction of the auroral oval in the midnight sector. The time scales of the expansion and the contraction of the auroral oval are found to be about 45 minutes and 8 hours, respectively. An empirical formula including these two time scales to predict the oval location from variations in the interplanetary magnetic field (IMF) is devised. The correlation coefficient between the measured and the predicted boundary is 0.82.