The Effect of Winds and Ocean Currents on the Annual Variation in Latitude

An elliptical excursion (mean diameter 20 feet), described annually by the pole of instantaneous rotation over the earth's surface, has been deduced from precise astronomic observations of latitude. According to Jeffreys and Rosenhead, most of this excursion can be ascribed to the seasonal variation in the distribution of matter (air, water, snow and vegetable matter). The most important single factor is the gain, in winter, of air mass over the Asiatic continent, and the corresponding loss over the Atlantic and east Pacific oceans. In this paper, it is shown that the effect of winds may be far from negligible. Here the important factor is the pressure against the Himalayas during the monsoon winds. Ocean currents account for only 1 per cent of the excursion. It is suggested that the latitude observations, together with related astronomic observations concerning an annual change in the length of day, provide a promising method for measuring certain fundamental modes in the annual oscillation of the atmosphere.