Effect of solar wind speed variations on other interplanetary parameters

Abstract

The daily values of interplanetary solar wind parameters as well as that of the geomagnetic disturbance index (Ap) have been used for the years 1965-2006. Long-term averages have been calculated for all those days when simultaneous data is available for all these parameters (V, B, Bz and Ap). Earlier reports have usually underlined the importance of V in producing terrestrial effects. As such, individual days have been grouped, in accordance with the limited range of V, in seven groups by the method of iteration using K-mean clustering (data mining) technique. Having selected days in each of the seven groups (ranges), the group averages, have been calculated for the entire period for V, B, VB and Ap along with their standard errors. The method has been further repeated for the individual solar cycles. These group averages have been used to investigate the statistical relationships between V, B, VB and Ap in different combinations. The results so obtained can be summarized as: (i) the monotonic increase of group average V is almost similar to that of increasing average values of Ap, and VB from groups 1 to 7; (ii) For each of the seven groups, VB <i style="">vs</i> Ap and B <i style="">vs</i> Ap have been always found to be better correlated (‘r’ larger) on a day-to-day basis, whereas V <i style="">vs</i> Ap has low values of ‘r’; (iii) the direction of Bz when negative is very much effective in producing larger Ap as compared to days when Bz is positive, in all the seven groups (more prominently in the last four groups of larger V). The statistical results obtained signify that the product VB is very effective in producing large scale geomagnetic disturbances.