Winter Anomaly in the F2 Region over Delhi

199-204The winter anomaly of f0F2 values on quiet and disturbed days around the lowest phase of solar activity (1962-65), has been studied using three techniques namely, (i) variation of noon f0F2, (ii) rates of change or f0F2 before and after noon, and (iii) analysis of the ionograms around the F1 maximum by overlay technique. The first two techniques have been used for making a morphological study of the anomaly and, the third one yields a quantitative estimate of the factors affecting the anomaly. The winter anomaly in f0F2 is shown to be accompanied by a stratification of the F-region into F1 and F2. The main cause of the anomaly seems to be a seasonal change in the rate of electron loss. Also, the ratio of linear loss coefficients from summer to winter seasons has been calculated for different solar activity years and for quiet and disturbed days, separately. Based upon this analysis it is confirmed that the increase in loss-rate during summer is responsible for the winter anomaly