Lunar oscillations in the D-region absorption at Singapore

Abstract

Lunar oscillations in the D-region, deduced from the analysis of absorption of vertical pulsed radio waves reflected from the E-layer of the ionosphere, have been reported for the stations at Slough, Pennsylvania, Freiburg, Ibadan and Colombo. For high latitude stations (Slough, Pennsylvania and Freiburg) the lunar time of maximum absorption is about 10 h as against around 3 h for the equatorial stations (Ibadan and Colombo), suggesting a possible phase reversal of lunar tides in the D-region between high latitude and equatorial regions. This communication describes the results of lunar semimonthly variations in the noon values of absorption (L) averaged for the frequencies 2.0, 2.4 and 2.6 MHz at Singapore, during the period April 1951 to May 1955.