Probabilistic forecasting analysis of geomagnetic indices for southward IMF events

Abstract Geomagnetic disturbances that drive space weather impacts such as ground‐induced currents and radiation belt enhancements are usually driven by strong southward interplanetary magnetic field (IMF) intervals. However, current heliospheric models either do not predict or provide low‐accuracy forecasts of IMF B z . Here we examine the probability distribution function of geomagnetic activity indices for southward IMF intervals. We analyze the in situ plasma and magnetic field measurements long‐duration large‐amplitude southward IMF intervals (called B s events). The statistical profiles of other solar wind and IMF parameters show significant differences during the periods 1 day before the B s events for different solar wind transients (such as interplanetary coronal mass ejections and stream interaction regions). As is well known, we find that the solar wind speed is positively correlated with geomagnetic indices and that strong southward IMF is the key in storm triggering but not necessarily for substorms. We find that the solar wind density weakly affects geomagnetic field activity, but the response depends on the type of solar wind transient that includes the strong B s events. We also find that magnetospheric ultralow‐frequency waves are induced by both strong southward IMF and solar wind dynamic pressure disturbances. We suggest that strong B s events could be predicted from the preceding characteristics of solar wind and IMF changes and that probabilistic forecasting of geomagnetic activity occurrence is potentially useful in space weather forecasting. We present preliminary analysis to demonstrate the out‐of‐sample ability to predict IMF B s events with in situ solar wind data.