Investigation of ionospheric absorption on 5·65 Mc/s at Waltair

Abstract

This paper presents the results of ionospheric absorption measurements conducted at Waltair (Latitude 17.7°N, Longitude S3.3°: E and Geomagnetic Latitude 7.4°N) during the International Geophysical Year and International Geophysical Co-operation periods on a frequency of 5.65 Mc/s. The solar zenith distance variation of diurnal and seasonal data of absorption follows a law of the form 8.7 ¦log_ep¦ = A₁ · (ƒ)^-2 · cosⁿ % dB only as an approximation. The variation of the cos % index has a significant negative correlation with Zürich relative sunspot number R. The monthly mean diurnal variation as well as seasonal noon-time variation of absorption confirms, more precisely, to a law of the form ¦log_ep¦ = A' + B . F(ƒ₀E/ƒ) cos % nepers where A' is a constant expected to refer to the non-deviative absorption in lower D-region. A' is found to vary linearly with R. A method is suggested to estimate the relative amounts of D- and E-region absorption at noon from the cos % index data. The absorption ¦log_ep¦ and A' are found to vary inversely as the square of the operating frequency.