Improving Multiday Solar Wind Speed Forecasts

We analyze the residual errors for the Wang-Sheeley-Arge (WSA) solar wind speed forecasts as a function of the photospheric magnetic field expansion factor (f(p)) and the minimum separation angle (d) in the photosphere between the footpoints of open field lines and the nearest coronal hole boundary. We find the map of residual speed errors are systematic when examined as a function of f(p) and d. We use these residual error maps to apply corrections to the model speeds. We test this correction approach using 3-day lead time speed forecasts for an entire year of observations and model results. Our methods can readily be applied to develop corrections for the remaining WSA forecast lead times which range from 1 to 7 days in 1-day increments. Since the solar wind density, temperature, and the interplanetary magnetic field strength all correlate well with the solar wind speed, the improved accuracy of solar wind speed forecasts enables the production of multiday forecasts of the solar wind density, temperature, pressure, and interplanetary field strength, and geophysical indices. These additional parameters would expand the usefulness of Air Force Data Assimilative Photospheric Flux Transport-WSA forecasts for space weather clients.

Automated summary

We analyze the residual errors in Wang-Sheeley-Arge (WSA) solar wind speed forecasts and find the systematic relationship between the residual speed errors and the photospheric magnetic field expansion factor and the minimum separation angle in the photosphere. By using these residual error maps, we apply corrections to the model speeds and test this correction approach using 3-day lead time speed forecasts. The improved accuracy of solar wind speed forecasts enables the prediction of multiday forecasts of various parameters, expanding the usefulness of the WSA forecasts for space weather clients.