Geoeffectiveness (<i>Dst</i> and <i>Kp</i>) of interplanetary coronal mass ejections during 1995–2009 and implications for storm forecasting

<jats:p>We summarize the geoeffectiveness (based on the <jats:italic>Dst</jats:italic> and <jats:italic>Kp</jats:italic> indices) of the more than 300 interplanetary coronal mass ejections (ICMEs) that passed the Earth during 1996–2009, encompassing solar cycle 23. We subsequently estimate the probability that an ICME will generate geomagnetic activity that exceeds certain thresholds of <jats:italic>Dst</jats:italic> or <jats:italic>Kp</jats:italic>, including the NOAA “G” storm scale, based on maximum values of the southward magnetic field component (<jats:italic>B</jats:italic><jats:sub><jats:italic>s</jats:italic></jats:sub>), the solar wind speed (V), and the y component (<jats:italic>E</jats:italic><jats:sub><jats:italic>y</jats:italic></jats:sub>) of the solar wind convective electric field <jats:italic>E</jats:italic> = −<jats:italic>V</jats:italic> × <jats:italic>B</jats:italic>, in the ICME or sheath ahead of the ICME. Consistent with previous studies, the geoeffectiveness of an ICME is correlated with <jats:italic>B</jats:italic><jats:sub><jats:italic>s</jats:italic></jats:sub> or <jats:italic>E</jats:italic><jats:sub><jats:italic>y</jats:italic></jats:sub> ≈ <jats:italic>VB</jats:italic><jats:sub><jats:italic>s</jats:italic></jats:sub> in the ICME or sheath, indicating that observations from a solar wind monitor upstream of the Earth are likely to provide the most reliable forecasts of the activity associated with an approaching ICME. There is also a general increase in geoeffectiveness with ICME speed, though the overall event‐to‐event correlation is weaker than for <jats:italic>B</jats:italic><jats:sub><jats:italic>s</jats:italic></jats:sub> and <jats:italic>E</jats:italic><jats:sub><jats:italic>y</jats:italic></jats:sub>. Nevertheless, using these results, we suggest that the speed of an ICME approaching the Earth inferred, for example, from routine remote sensing by coronagraphs on spacecraft well separated from the Earth or by all‐sky imagers, could be used to estimate the likely geoeffectiveness of the ICME (our “comprehensive” ICME database provides a proxy for ICMEs identified in this way) with a longer lead time than may be possible using an upstream monitor.</jats:p>