Effects of solar wind dynamic pressure and preconditioning on large geomagnetic storms

We investigate the effects of solar wind dynamic pressure, P-dyn, and preconditioning in 88 large magnetic storms (Dst < -100 nT) occurring during solar cycle 23. We have developed an improved model of the Dst profile, based on a modified Burton equation, where additional effects of Pdyn and diminished Dst pressure-correction have been taking into account. On the average, our model predicts the Dst peak values within 9% of observations and gives an overall RMS error of 11%, which is an improvement over those models whose injection functions only depend on the solar wind electric field. The results demonstrate that there is an increase in the Dst peak value when there is a large enhancement of Pdyn during the main phase of a storm. The average increase of the storm intensity is estimated to be 26% for 15 storms with the max (P-dyn) > 15 nPa. We find that the preconditioning in multi-step Dst storms plays no significant role in strengthening the storm intensity, but increases the storm duration.