MAE and standard deviation (shown as error bars) of background solar wind predictions by month during 2007–2016. From top to bottom: the MAE and standard deviation of solar wind speed (V _sw), proton density (ρ), strength of magnetic field (B), and the accuracy of polarity of magnetic field forecasts. The red, green, and blue lines represent the MAE of the results of function 1, 2, and 3, respectively.