Solar events and solar wind conditions associated with intense geomagnetic storms

Intense magnetic storms pose a systemic threat to the electric power grid. In this study we examined the solar/interplanetary causes of such storms, their peak theoretical and observed intensities, and their occurrence frequency. Using coronal mass ejection (CME) and solar wind data, we selected the 18 intense magnetic storms from 1996 to 2021 with disturbance storm time (Dst) index of less than - 200 nT and analyzed solar events and solar wind conditions associated with them. Approximately 83% of the CMEs associated with the storms were full halo type and more than 83% of the flares associated with the storms were located within 30 degrees in longitude of solar central meridian. The integrated dawn-to-dusk electric field in the solar wind (E-y) showed a good correlation with |min. Dst| of the storms and the peak E-y (E-yp) and the peak southward interplanetary magnetic field showed next good correlations with |min. Dst|. We obtained the E-yp of 236 mV/m for |min. Dst| of 2500 nT of the expected upper limit of Earth's magnetosphere using the empirical equations from the correlations between |min. Dst| and solar wind parameters and showed that this value of E-y is possible according to the past observations. The E-yp of 54 mV/m for the 13 March 1989 storm and that of 165/79 mV/m for the Carrington storm (|min. Dst|= 1760/850 nT) were also obtained. The analysis using the complimentary cumulative distribution function suggested the probabilities of E-y of 100, 200, 250, and 340 mV/m over the next 100 years to be 0.563, 0.110, 0.060 and 0.026, respectively.