Dependence of Great Geomagnetic Storm (ΔSYM-H≤-200 nT) on Associated Solar Wind Parameters

We use Delta SYM-H to capture the variation in the SYM-H index during the main phase of a geomagnetic storm. We define great geomagnetic storms as those with Delta SYM-H <= -200 nT. After analyzing the data that were not obscured by solar winds, we determined that 17 such storms occurred during Solar Cycles 23 and 24. We calculated time integrals for the southward interplanetary magnetic field component I (B-s), the solar wind electric field I (E-y), and a combination of E-y and the solar wind dynamic pressure I (Q) during the main phase of a great geomagnetic storm. The strength of the correlation coefficient (CC) between Delta SYM-H and each of the three integrals I (B-s) (CC = 0.73), I (E-y) (CC = 0.86), and I (Q) (CC = 0.94) suggests that Q, which encompasses both the solar wind electric field and the solar wind dynamic pressure is the main driving factor that determines the intensity of a great geomagnetic storm. The results also suggest that the impact of Bs on the great geomagnetic storm intensity is much more significant than that of the solar wind speed and the dynamic pressure during the main phase of an associated great geomagnetic storm. The better estimation of the intensity of an extreme geomagnetic storm intensity based on solar wind parameters is also discussed.