Analyses on Solar Microwave Bursts & Associated Sudden Ionospheric Disturbances in Relation to the Phases of the H«-flares

277-281Occurrences of the flare-associated microwave bursts reported during the period 1969-72 at eight frequencies have been examined in relation to the two flare phases namely: (i) pre-maximum phase defined to be the time interval between the starting and the peak of the flare, and (ii) post-maximum phase defined to be the time interval between the peak and the end of the flare. Peak flux and the energy excess spectra of these flare-associated bursts as well as their association with different types of sudden ionospheric disturbances (SIDs) have also been examined in the present analysis. Some of the important results obtained are: (i) About 76% of the flare-associated bursts occur in the pre-maximum phase and the remaining 24% occurs in the post-maximum phase of the flare irrespective of any flare classification; (ii) Microwave "impulsive" and "gradual rise and fall" (GRF) bursts are relatively more important in the pre-maximum phase of the flare. "Impulsive" bursts seem to be more associated with flares having relatively small ratio of rise-time to duration while the reverse is true for the "GRF" bursts. "Post-burst increase" (PBI) type of bursts show comparatively higher occurrences in the post-maximum phase; (iii) Peak flux and energy excess spectra of the concurrent microwave bursts in the pre-maximum phase are mostly of the "inverted U" and "increasing with frequency" spectral types. Of these, "impulsive" bursts are predominantly of the "inverted U" and the "GRF" bursts are of the "increasing with frequency" type; and (iv) Microwave bursts occurring in the post-maximum phase of the flare have also been found to be associated with different Sills. However, their percentage association values are much smaller than those in the pre-maximum phase