Forecasting the Dst index from L5 in-situ data using PREDSTORM: accuracy and applicability

STEREO-B and STEREO-A are both important proxies for potential solar wind monitors at the Sun-Earth L5 point. In this study, measurements from STEREO-B are used to determine how well the Dst index in particular can be predicted using data measured near the L5 point. This is useful for determining the geoeffectivity of storms resulting from high-speed solar wind streams. Observed solar wind speeds are first mapped to the near-Earth environment as if they had been measured at L1, and the Dst is predicted from the data using a solar wind-to-Dst model. We find that Dst predicted from L5 data performs better than a recurrence model assuming the solar wind conditions repeat every 27 days, although not as well as when predicted from L1 data. The newly developed approach is currently implemented in the PREDSTORM software package to provide a real-time Dst forecast using STEREO-A data.