Relationship between nighttime total electron content enhancements and VHF scintillations at the equator

Abstract

The relationship between nighttime enhancements in total electron content (TEC) and VHF amplitude scintillations has been studied using the ATS 6 satellite data obtained from two closely located equatorial stations (Ootacamund and Thumba) for the period October 1975 to July 1976. The results show that the occurrence and various other characteristics of the TEC enhancements are correlated to corresponding characteristics of the scintillation index SI . The peak value of the SI index is found to increase linearly with that of the TEC enhancement until it reaches the saturation value of nearly 1 for the peak TEC enhancement of about 0.6 × 10¹⁷ m^-2. Both phenomena start mostly prior to midnight with the TEC enhancement being delayed by 1 to 1½ hours with respect to the scintillations. The half-amplitude duration of the scintillation enhancement is greater than that of the TEC by a factor of 1 to 2. The intensity and duration of both phenomena are found to be maximum at equinox and minimum in summer. From the results it is clear that the TEC enhancements cannot be regarded as a source for the small-scale irregularities but rather they both seem to depend on the postsunset vertical drifts in the F layer.