Variation of D-Region Absorption at Delhi

Abstract

Absorption measurements have been made at Delhi during midday using the Al technique for the period October 1969 to December 1970. The radio frequency used was 5·7 MHz. Ionograms taken during this period have been analyzed for true heights. The absorption suffered by the radio wave up to the height of reflection has been calculated using the experimental <i>N</i>(h) profile and an assumed model of electron collision frequency. This calculated absorption has been divided into two parts: (a) absorption suffered in the E-Iayer L(E) On the height range 95-160 km) and (b) absorption in the F-Iayer <i>L</i>(F) (from 160 km to the height of reflection). It is round that the total calculated absorption <i>L</i>(E)<i>+L</i>(F) is always less .than the experimental value. This is attributed to the absorption in the D-region (below 95 km), denoted by <i>L</i>(D)<i>. </i> It is found that <i>L</i>(D) is maximum in equinoxes with low values in summer and wiater.