The Earth's Rotation and Atmospheric Circulation —II. The Continuum

Summary In an earlier paper (Lambeck & Cazenave, Part I) we investigated the seasonal variations in the Earth's rotation and their relation to the global wind circulation. In this paper we consider mainly the high frequency part of the length‐of‐day spectrum. A month‐by‐month evaluation of the zonal wind excitation function shows that these rotational variations are all of zonal wind origin for frequencies up to at least 6 cycles per year. The zonal winds also contribute to frequencies greater than 6 cpy in the Earth's rotation and will degrade the results for the Love numbers k 2 estimated from the tidal terms near 13 and 26 cpy. Rapid changes of as much as 10 ‐8 during 5 days have been observed in the length of day on several occasions and these are also caused by meteorological disturbances. Any study of other possible excitation functions will require that these meteorological contributions are first evaluated. There does not appear to be any single wind pattern that is responsible for the observed high frequency variations in the length of day and it does not seem possible to use these observations as an indication of the nature of the zonal wind pattern other than as a global zonal wind index. There is some evidence that the zonal winds will contribute to those long‐period variations in the Earth's rotation that are usually attributed to core‐mantle coupling.