Effects of fast and slow solar wind on the correlations between interplanetary medium and geomagnetic activity

Abstract

The coupling between interplanetary parameters and geomagnetic activity has been investigated. In particular, the correlations between the interplanetary medium and the geomagnetic indices Kp and Dst have been calculated for different ranges of solar wind speed. The correlation coefficients obtained for data points corresponding to solar wind slower than 550 km/s are equal or slightly higher than the global correlations. The observations show generally lower correlation coefficients for solar wind speeds faster than 550 km/s. These results suggest that at high solar wind speeds the processes responsible for the energy transfer between the interplanetary medium and the magnetosphere saturate. In addition, the influence of internal magnetospheric plasma physics on the geomagnetic activity may be larger for the faster solar wind intervals. In the context of the deterministically chaotic approximations we discuss how the threshold at ~550 km/s might represent the break of the order in the interplanetary-geomagnetic coupling system, so that the linear correlations or the correlations with a relatively weak departure from linearity are significant mostly during the slower solar wind. Copyright 2002 by the American Geophysical Union.