The cross-polar potential drop and its correlation to the solar wind

The cross-polar potential drop Phi(pc) as derived from the FAST satellite is used to study the average magnetospheric response to changes in the solar wind as monitored by the Wind spacecraft. The coupling of the solar wind with the magnetosphere is examined using the interplanetary magnetic field (IMF) B-z, the model reconnection electric field vB(t)sin(k)(theta/2) for k=3, 4, and the Akasofu-Perreault epsilon parameter. Initial results comprising 37 cases of Phi(pc) show one major response of the magnetosphere to the solar wind forcing at 15 min time lag followed by two minor pulses at 55 min and 105 min, respectively, during times when the IMF polarity was mainly southward and the geomagnetic activity was moderate to low. Phi(pc) shows a very good correlation with typical models of the reconnection electric field at 15 min time lag, reaching a maximum linear correlation coefficient of r=0.95 for vB(t)sin(3)(theta/2). In order to reach an understanding of the importance of individually calculated correlation coefficients, we introduce the statistical. bootstrap algorithm of Efron and Tibshirani [1993], which allows us to estimate a correlation coefficient standard error. In defining a quality measure based on this method, the significance coefficient s, we are able to interpret a resulting correlation coefficient time lag series in terms of a linear prediction filter similar to earlier techniques. The results on the magnetospheric response for Phi(pc) are further compared with those obtained using the geomagnetic indices Dst, SYM-H, and ASY-H. The similar magnetospheric response to the solar wind electric field for Phi(pc) and ASY-H at time delays of more than 40 min together with a high correlation coefficient between Phi(pc) and ASY-H suggest that these magnetospheric parameters couple to one another. The average dynamic response of the ionospheric convection to the solar wind electric field is in essential agreement with those reported by Klimas et al. [1994] on a normal magnetospheric mode with a recurrence frequency of 50 min.