Modeling the arrival at Earth of the interplanetary shock following the 12 May 1997 solar event using HAFv2 and 3‐D MHD HHMS models

The 12 May 1997 solar event is used to demonstrate the improvements that have been made in recent years in the accuracy of predicting, in the operational environment, the time of arrival at Earth of solar‐caused interplanetary shocks. This event provides a simple test case because it was both well isolated in time from other events and well documented, with the observation of a large flare (in optical and X‐ray), a large halo CME, metric type‐II radio burst and near‐Earth solar wind and interplanetary magnetic field data. The Hakamada‐Akasofu‐Fry model (version 2: HAFv2) near‐real‐time prediction gave an error of 31 h. Because the accuracy of predicted Sun‐to‐Earth transit times of such shocks depends both on the model and our ability to determine the proper inputs from available observations, we reexamined the predictions made for the 12 May event using inputs that could have been available in near‐real‐time, both with HAFv2 and a second, ensemble‐partnered solar wind prediction model, the 3‐D MHD Hybrid Heliospheric Model System (HHMS). We use updated methods of estimating the initial shock velocity (from Smith et al., 2005b) and examine the influence of the background solar wind. This reexamination reduced the error from the original 31 h to less than 4 h. Achieving near‐real‐time accuracies to this level would greatly enhance operations of technologies such as electrical power grids, satellite systems, and polar flight communications.