The forecasting of intense geomagnetic storms

Abstract

Intense geomagnetic storms are produced by the arrival at the magnetopause of solar wind carrying a magnetic field with a large southward component lasting for several hours. Solar and interplanetary processes have been considered to explain the presence of this field, but many aspects of its origin are still unclear. The general problem of forecasting intense geo- magnetic storms several days in advance from solar observations is discussed, reviewing the different approache.s taken so far and extending a previous study of the solar sources of major geomagnetic storms. All evidence favours the occurrence of an explosive event (fiare or prominence eruption) near a coronal hole and near the solar central meridian as a potentially geoeffective solar event. Comments are made on how our forecasting capability may improve with the use of soft X-ray im- ages of coronal transients, numerical MHD simulations of the generation and propagation of solar transients in the inter- planetary medium, and tracking of solar wind disturbances by means of interplanetary scintillation.