Determining the key drivers of magnetospheric Pc5 wave power

Abstract

Long‐period ground ULF waves may be controlled by the mean values of solar wind and interplanetary magnetic field (IMF) parameters (velocity, density, and North‐South IMF component Bz). We investigated the influence of these parameters on ground ULF power in the Pc5 range (2–7 mHz) during periods of quiet and during coronal mass ejection (CME) and corotating interaction region (CIR) storms from 1991 to 2004. With multiple regression and path analysis, we studied the influence of these hourly parameters as a set rather than individually. This allowed us to determine which factors were most influential and which were only correlated with influential factors. By using multiple regression, we have explained more variation in Pc5 power than has been achieved in previous studies. In both storm types (CME and CIR) and during all storm phases (initial, main phase, recovery, and a 48 h period after recovery) as well as during quiet periods, solar wind velocity and IMF Bz influenced ground Pc5 power directly. These two variables also acted on the ULF Pc5 indirectly through the intermediate parameters of Dst, and the variations in number density and IMF, although at a weaker level. Ground Pc5 power was greater during CME storms during the main phase and recovery but larger during CIR storms in the period after recovery. In addition, the effect of certain independent variables differed depending on storm type. A model such as this offers the possibility of nowcasting Pc5 power by inserting current levels of solar wind and IMF variables as predictors into the regression equation.