Frequency gap between fast drift and type III associated bursts

The frequency gap between the high-frequency fast drift bursts and metric type III associated bursts is interpreted using the collisional absorption of the radio emission in dense layers of the solar atmosphere. Studying the absorption of radio emission from the narrow, cold and dense filament which is embedded in hotter plasma and heated from the corona, it was found that the absorption causing the frequency gap has the maximum at about 1 GHz, in agreement with observations. Similar results were obtained also for the current sheet structure.