FILAMENT DISAPPEARANCES DURING THE PERIOD OF SEPTEMBER 1991 THROUGH SEPTEMBER 1994

Continuous full-disk H alpha images recorded by the Big Bear Solar Obs ervatory (BBSO) from 1 September 1991 to 19 September 1994 (the first three years of Yohkoh mission) were digitized and analyzed. The data s et consists of nearly 10 000 H alpha images, one every half hour for t he period when the BBSO was observing. Two statistical studies of the disappearing solar filaments based on this set of data are made: (1) T he disk latitude distribution of all larger disappearing filaments wit h a minimum length of 70 are sec, including the time of their disappea rance. Of the 1095 such filaments, 439 disappeared during our continuo us observations, 314 disappeared during the BBSO night gap, 162 disapp eared during data gap (more than 94 hours) and 180 rotated beyond the west: limb. If we plot latitudes as a Function of time for all these d isappeared filaments, it shows a uniform distribution in latitude. How ever, if we plot the distribution of larger disappeared filaments (200 are sec or above), then the butterfly trend appears - position of fil aments tends to drift to lower latitude as solar activity decreases. ( 2) The disk distribution of all detectable disappearing filaments. lar ge and small, for the 9-months period, January 1994 to September 1994. We find that the size distribution of 351 collected disappeared filam ents follows a power law with a power index of -1.40.