On the group delay and the sign of frequency drift of solar type III radiobursts

It is shown that the positive frequency drift sometimes observed in the hig h-frequency part of type III bursts can be explained by a decrease in the s ignal group delay as the emission source moves in the direction of decreasi ng density. This effect is detemined fundamentally by the density distribut ion along the propagation path of electromagnetic waves. It is considered t o reflect the influence of magnetic field on the group delay.