Improving Multiday Solar Wind Forecasts

Abstract:

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 residual errors are systematic when examined as a function of f_p and d. We use the array of average residual errors as a function of f_p and d to apply a correction to the model speeds based on the corresponding model f_p and d values. We test this correction approach using 3-day lead time speed forecasts for an entire year of observations and model results. The WSA model also produces forecasts with lead times ranging from 1 to 7 days in 1-day increments. Our methods can readily be used to develop corrections for the remaining forecast lead times. 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, geophysical indices, and a wide variety of space weather conditions.