Winter Anomaly in Ionospheric Absorption of Radio Waves over Half a Sunspot Cycle

219-223The winter anomaly in ionospheric absorption is studied at a mid-latitude station over half a solar cycle. It is shown that the anomalous increases of absorption on some days in winter are better correlated with 10 mb-level geopotential height than with temperature at that level. The anomaly is most marked in the month of January. It was about 168% in 1964 and 79% in 1969. The present results along with those reported by others earlier are evidences to suggest that the possible cause of winter anomaly in ionospheric absorption may be an Increase in ionization In the D and probably in the E regions of the ionosphere following disturbances in the pressure and wind circulation system at stratospheric and mesospheric levels