Air density variations in the mesosphere, and the winter anomaly in ionospheric absorption

A recent paper by Jones, Peterson, Schaeffer, and Schulte [1959] reporting large mesospheric air density variations at high latitudes in winter may be of considerable interest regarding the anomalous winter daytime absorption of medium-and high-frequency radio waves. A plot of noon absorption of vertically reflected 2 Mc/s radio waves at Slough from year to year shows that the absorption in winter is usually much greater than would be expected if it were simply related to the zenith angle of the sun [Whitehead, 1957]. Noon absorption has been measured over long periods at low as well as at high latitudes, but the effect has been reported only in the event of the latter. It is not present, for instance, in the absorption measured at Singapore and published in the Slough Bulletin.