Predictability of <i>Dst</i> index based upon solar wind conditions monitored inside 1 AU

Abstract

The formula of Burton et al . [1975] provides a quick and simple means by which the strength of the ring current and the Dst index can be calculated based solely on upstream solar wind density, velocity, and the north/south component of the magnetic field. Solar wind data from ISEE 3, the Pioneer Venus Orbiter, and Helios A are used to show how well Dst predictions based on the Burton et al. formula match Dst observations for upstream monitors at various heliospheric distances. It is shown that a solar wind monitor that provides a substantial geomagnetic forecast lead time, with usable predictions of the characteristics of the solar wind, can be stationed ∼0.7 AU if it is near the ecliptic plane and within 10° east to 5° west of the Earth‐Sun line. It is also shown that the Burton et al. formula predicts equally well the Dst index resulting from the passage of disturbed solar wind, associated with either interplanetary coronal mass ejections or streaminteraction regions. A solar sail‐type spacecraft is proposed as the ideal monitor for forecasting purposes.