Some Studies on Long Wave Propagation & Other SID Effects

Abstract

Continuous recordings of received sky wave field-strength from Radio Tashkent (164 kHz, 41° 25'N; 69° 12'E;1634 km from Delhi) have been going on for the past 20 years in the Research Department of All India Radio. Analysis of the data has shown that sudden changes in amplitude of the received If signal (abbreviated as SCL) is almost always associated with the occurrence of solar flare. Using the field strength data, certain parameters of lower ionosphere like reflection height from sunrise effect and recombination coefficient from the post-flare variation 'of If signal, have been evaluated. Some further studies of lower ionosphere using SID' effects; SCL and X-ray flare data. have revealed that the effective X-ray region responsible for causing the different types of SCL and other SID effects like SPA and SCNA lies within 1-2A and a flux energy of 10^-3 to 10^-4 erg cm^-1 sec^-1. Analysis of SCNA data at 18 and 29 MHz has indicated that the height of maximum absorption is around 68 km. An attempt has also been made to explain the occurrence of different types of SCLs vis-a-vis the nature of X-ray flares.