Solar flares and coronal shock waves

The ignition of coronal shock waves by solar flares is investigated confronting the results of a simple MHD model with the observations. Characteristics of type II bursts recorded in the metric and decametric wavelength range are compared with the properties of the microwave and soft X-ray bursts of the associated flares. The time delay of the type II burst beginning after the onset of a flare is found to be shorter for shorter rise time of a flare burst and for a more powerful flare. Starting frequencies of type II bursts are higher for more impulsive flares. Instantaneous relative bandwidths of the type II bursts are larger for more powerful flares, indicating a higher Mach number of the shock. Consistent with this, a positive correlation between the flare importance and the inferred shock velocity is found. The results are fully consistent with the implications of the model describing the shock formation by a flare-ignited blast wave.