Annual and semiannual variations in the length of day, related to geophysical effects

Abstract

Using exact time observations for the years 1958 through 1963, a re-examination is made of the seasonal variations in length of day and their relation to geophysical effects. For the most important parameter, the relative angular momentum of the atmosphere, a large body of aerological data has been evaluated, which was not available when Mintz and Munk carried through the first study of this kind about 15 years ago. The seasonal change of atmospheric mass over the Antarctic is introduced as an additional minor effect. The other geophysical phenomena contributing to the annual and semiannual variations of the length of day are used as given in Munk and MacDonald's recent monograph on the rotation of the earth. The result is that there remains a semiannual term in the yearly march of the length of day that cannot be explained by known geophysical effects, too large to be considered an error effect alone.