Dependence of great geomagnetic storm intensity ($\Delta$SYM-H$\le$-200 nT) on associated solar wind parameters

TL;DR

This study investigates how solar wind parameters, especially the combined effect of electric field and dynamic pressure, influence the intensity of great geomagnetic storms, providing insights into predicting such extreme space weather events.

Contribution

It identifies the solar wind dynamic pressure combined with the electric field as the primary factor influencing the strength of great geomagnetic storms, based on correlation analysis.

Findings

Q parameter has the highest correlation with storm intensity (CC=0.94)

B$_s$ influence is less significant than Q during main phase

11 great storms analyzed during solar cycle 23

Abstract

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 $\le$ -200 nT. After analyzing the data that were not obscured by solar winds, we determined that 11 such storms occurred during solar cycle 23. 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 = 0.74), I(E$_y$) (CC = 0.85), 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 B$_s$ 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 associated great geomagnetic storm. How to estimate the intensity of an extreme geomagnetic storm based on solar wind parameters is also discussed.