Some studies on the association of solar optical flares and microwave bursts with sudden ionospheric disturbances

Abstract

The association of solar optical flares (numbering 8230) reported under the dualclassification and also of different types of microwave bursts (numbering 1670) with the sudden ionospheric disturbances (SID's) during the peak phase of current solar cycle (cycle 20) have been examined. Important results obtained are: 1. (1) Percentage association of flares with SID's of all types increases with the intensity of the flares irrespective of their areas; 2. (2) Out of 51 flares associated simultaneously with all the six different types of SID's, 37 were of bright intensity (b), and only two were of large area (class 3); 3. (3) Microwave burst-SID association increases with the increase of peak flux. Further, percentage association is higher when the bursts are complex or contain 'fluctuations'; 4. (4) Of the 47 microwave bursts associated simultaneously with all the six SID's, 83 per cent show fluctuations; 5. (5) SFD's are found to have their peaks attained earlier than those of both the associated flares and microwave bursts. Results obtained from the present investigation lead to the conclusion that a bright flare with an associated microwave burst of either complex type or having fluctuations is a true indication of the simultaneous occurrences of all the different types of sudden ionospheric disturbances.