Hybrid model for nowcasting and forecasting the K index

A new empirical model nowcasting and predicting a proxy to the geomagnetic K index is developed, which is based on the combined use of solar wind parameters and ground-based magnetic data. The present approach implements the previously developed solar wind-based MAK model, calibrating its values with magnetogram-derived K index. The new model is named as Hybrid Dourbes K (HDK) model. The HDK nowcast model provides the quantity Kdf, obtained by solar wind-based Ksw and corrected with a combination of differences between several past values of Kd and Ksw. The model error of the nowcast Kdf is found to be 0.38 KU, or nearly twice less than that of the MAK model. Kdf has a good predictability. Prediction made by weighted extrapolation 6 h ahead carries an error of 1.0 KU, while for the first 1 h the error is 0.58 KU only.