Decrease of 2800 MHz solar radio emission associated with a moving dark filament before the flare of May 19, 1969

A decrease in the total flux at 2800 MHz, or a negative burst was observed 15 min before the onset of the short duration, impulsive burst of May 19, 1969 at 14:30 UT and continued for another 16 min. It had been recognized originally in the records from the Algonquin Radio Observatory only as a fluctuation in a long enduring, gradual rise and fall event which had commenced at 12:40 UT. A detailed account of the radio flux variations in relation to the optical activity as described by Vorpahl (1973) is given and indicates that the onset of the negative burst and the southward motion of a dark filament are associated.Presented at 140th Meeting of the American Astronomical Society, June 1973, Columbus, Ohio.