Abstract

The speed of a shock that precedes ejecta from a solar energetic eruption is one of the key parameters used for input by many numerical models that predict the arrival of interplanetary shocks at Earth. These shocks are likely to be followed by significant geomagnetic activity. Near‐real‐time “fearless forecasts” of shock arrival times at the L1 libration point have been made for more than 6 years with several models. Initially, these models used, for input speeds near the Sun, speeds obtained from observations of metric type II radio bursts that are signatures of shocks propagating out through the solar corona. More recently, speeds of halo/partial halo coronal mass ejections (CMEs) were also considered in these models as another measure of shock speeds close to the Sun. During the period of high solar activity in October–November 2003, the data required for input into the models were often available in near real time from a number of observing stations. Therefore the fearless forecasts were issued in some cases with alternative inputs. These forecasts provided a basis on which to compare the success of the predictions (in terms of how close each prediction of the shock arrival time was to the observed time). The results of the analysis of this data set provide guidelines for selecting the input speed for shock propagation models. Both CME and metric type II radio burst measurements are shown to be useful and complementary. In general, the highest speed gave the best predictions. This demonstrates the desirability of having coronagraph data available for operational use.

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