A study of SFA on 164 KHz for Tashkent-Delhi propagation

A detailed study of flare effects on 164-KHz field-strength for Tashkent-Delhi propagation has revealed that the observed change in signal due to flare belongs to one of the following three types: (1) type I events, characterized by a rapid increase in the signal followed by an approximately exponential decay, are found to be due to type I and the softer of type II flares classified by Sengupta (1971 and 1974); (2) type II events are correlated with Sengupta's type II flares and are characterized by an initial dip in the signal followed by a rapid increase and an approximately exponential decay after the maximum; (3) type III events are due to Sengupta's type III and the harder of type II flares and are characterized by rapid decrease in the signal followed by slow recovery. Theoretical calculations are made to show that this behavior can be explained fully in terms of lowering of the D-layer height and change in the electron density gradient at the bottom of the D-layer.