Forecasting Dst index using CME expansion speed

It is well known that solar eruptive phenomena, in particular coronal mass ejections (CMEs), their corresponding interplanetary counterparts (ICMEs) and driven shocks are the main origins of southward-directed Bz, which drive geomagnetic disturbances. The ability to predict geomagnetic storms, however, is still a big challenge because details on this Bz fields are difficult to be obtained with a lead time of tens of hours to days. If estimates of Bz and solar wind speed at 1AU are available, it is possible to derive the peak Disturbance Storm-Time Dst index using Burton et al. (1975) formula. Previous works have addressed empirical methods to obtain Bz from total magnetic field strength and solar wind velocity inside interplanetary magnetic clouds. Empirical estimates of ICME speeds at 1AU from CME speeds measured in coronagraphs have also been proposed. In this work, an attempt is made to forecast the geomagnetic Dst index using observations of coronal mass ejection (CME) expansion speed observed in coronagraphs. Only those cases in which a CME was associated with a magnetic cloud at 1 AU are addressed.