The Earth's rotation and atmospheric circulation

Abstract

The excitation of the Earth's rotation by the zonal wind circulation has been evaluated for a 22 yr period and the astronomical observations of the length‐of‐day from 1958 to 1980 have been corrected for this contribution as well as for tidal effects. The spectrum of the excitation contains, in addition to the seasonal terms and other high‐frequency fluctuations (˜ 1 cycle per 9 month and ˜ 1 cycle per 4 month), significant power at periods up to about 50 month. The spectrum of the length‐of‐day fluctuations corrected for winds and tides contains significant power only at periods above about 50 month. Other‐than‐atmospheric excitation mechanisms are required to explain this part of the length‐of‐day spectrum. Both the astronomical and wind data suggest that fluctuations occur in the amplitude of the annual term with maximum amplitude occurring at about 10 year intervals (1958–1960, 1968–1970, and 1977–1979). Show more