Comment on “Effects of fast and slow solar wind on the correlation between interplanetary medium and geomagnetic activity” by P. Ballatore

Abstract

Ballatore [2002] has investigated the correlations between the interplanetary medium and the geomagnetic indices Kp and Dst for different ranges of solar wind speed. She found that the correlation coefficients obtained for data points corresponding to a solar wind slower than 550 km s−1 are equal to or slightly higher than the global correlations. The observations show generally lower correlation coefficients for solar wind speeds greater than 550 km s−1. From these results she verified that at high solar wind speeds the processes responsible for the energy transfer between the interplanetary medium and the magnetosphere saturate. We have recalculated the correlation coefficients using the most recent OMNI data and found, contrary to her results, that the global correlation coefficients between Kp, Dst, and the interplanetary parameters are generally higher than the correlations obtained for data points corresponding to different solar wind speed intervals. From statistical tests we demonstrate that the correlations for solar wind speeds greater than 550 km s−1 are not significantly different from the correlations in other solar wind speed intervals. There is insufficient evidence to show that, from an investigation of the correlation coefficients between the interplanetary medium and the geomagnetic indices Kp and Dst, a threshold exists at a solar wind speed of ∼550 km s−1 for the coupling of the interplanetary‐magnetosphere system. This conclusion is also supported by analysis of the correlations between the time derivation of Dst and the interplanetary medium.