Dependence of Major Geomagnetic Storm Intensity (Dst ≤−100 nT) on Associated Solar Wind Parameters

We investigate the influence of various solar wind parameters on the intensity of the associated major geomagnetic storm. SYM-H_min was used to indicate the intensity of major geomagnetic storms, while I (B_s), I (E_y) and I (Q ) were used to indicate the time integrals of the southward interplanetary magnetic field component (B_s), the solar wind electric field (E_y), and Q, which is the combination of E_y and the solar wind dynamic pressure, during the main phase of a major geomagnetic storm, respectively. We have found that the correlation coefficient (CC) between the time integral of solar wind parameters and the intensity of an associated major geomagnetic storm has a physical meaning, while the CC between the peak value of a given solar wind parameter and the intensity of an associated major geomagnetic storm has no physical meaning. We used 67 major geomagnetic storms that occurred between 1998 and 2006 to calculate the CC between SYM-H_min and I (B_s), the CC between SYM-H_min and I (E_y), and the CC between SYM-H_min and I (Q ). The derived CC between I (B_s) and SYM-H_min is 0.33, while the CC between I (E_y) and SYM-H_min is 0.57, and the CC between I (Q ) and SYM-H_min is 0.86, respectively. These values indicate that I (B_s), I (E_y) and I (Q ) contribute in a small, moderate, and crucial way to the intensity of a major geomagnetic storm, respectively. For the solar wind to have a strong geoeffectiveness B_s plays a role, together the solar wind speed and density, but also the dynamic pressure > 3 nPa. Large and long duration B_s or E_y cannot ensure a major geomagnetic storm, if the solar wind dynamic pressure is much lower than 3 nPa.