Contribution of the atmosphere to the seasonal changes in earth's rotation

Using new data of atmospheric angular momentum for the period 1975-1995, th e contributions of the atmosphere to the changes in LCD and polar motion on the seasonal time scale are investigated. The results show that, when the effects of wind and atmospheric pressure are considered, the atmosphere's c ontribution on the annual and semi-annual time scabs may reach, respectivel y, 95% and 88%. We also give some quantitative results of the atmosphere's excitation of polar motion. On the annual time scale, the contribution to t he X-component of polar motion is 16% and that to the Y-component is 43%. O n the semi-annual time scale, the contributions to the X- and Y-components are, respectively, 9% and 30%. From the above results, it is clear that the contribution of the ocean should also be included in a more complete solut ion of the problem of excitation of the earth's rotation.