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.