Validating solar wind prediction models: A large speed enhancement index

One of the primary goals of the Center for Integrated Space-weather Modelling (CISM) effort is to assess and improve prediction of the solar wind conditions in near-Earth space, arising from both quasi-steady and transient structures. We compare 8 years of L1 in-situ spacecraft data with predictions of the solar wind speed made by the Wang-Sheeley-Arge (WSA) empirical model. Using the standard method of measuring prediction accuracy (i.e. by calculating the mean-square error (MSE) between the data and model) we test the 8 years of WSA predictions, and find the optimal lead-time for 1 AU solar wind speed predictions. However, we also highlight some potential problems with the interpretation of MSE, and put forward an additional, complementary, index based upon large speed enhancements (LSEs). A method for systematically selecting and associating LSEs from spacecraft and model data is outlined, and a "score" calculated based upon the model's hit to miss and false ratio, along with the timing and speed magnitude errors between the forecasted and observed LSEs. Furthermore, by defining discrete events it is also possible to use model predictions from above and below the ecliptic plane to predict timing errors in addition to the usual speed errors. Morphological differences between hit, miss and false LSEs are investigated to aid improvements to the model.