The Role of Solar Wind Dynamic Pressure in Determining the Intensity of the Geomagnetic Storm

Abstract

Super intense storms are unique, and their impacts are remarkable. The present study focuses on the super intense geomagnetic storms (SYM-H ≤ −300 nT) in solar cycles 23 and 25 to address critical questions such as what made a geomagnetic storm a super intense one, and the pivotal role of solar wind and interplanetary magnetic field parameters. The storms with significant steepening of SYM—H are examined, a factor P_dyn.B_z is introduced and correlation coefficient analysis is carried out. To address the complexity of storms, the correlations of solar wind energy input (Einj) with P_dyn.Bz and Esw are investigated and are found to be well correlated with coefficients of 0.94 and 0.89, respectively. The time integrated values of SYM-H during the storm period provide a higher correlation with VB_z and P_dyn.B_z than peak SYM-H values. The ideal combination of high values of P_dyn and VBz, that is, P_dyn ≥ 10 nPa and VBz ≥ 5 mV/m and duration play a major role in developing steep SYM-H (<−400 nT) as seen for the super intense geomagnetic storms. We can clearly state that the combination of high P_dyn and steady southward B_z is a key factor in deciding the intensity of the storm as the longer the duration of the combination led to larger peak values of SYM-H. MHD simulations have evidently shown that the crucial role of high solar wind density values for longer duration contributes to the steepening of SYM-H leading to super-intense geomagnetic storms.