Wind contributions to the Earth's angular momentum budgets in seasonal variation

The atmospheric contributions to seasonal variations in length of day (LOD) and wobble are discussed for the period 1988-1997, The data sets used here are SPACES; and EOP97C04 for LOD and wobble, respectively. Two atmospheric angular momentum (AAM) functions are calculated from the operational objec tive analysis data of the Japan Meteorological Agency (JMA) and the reanaly sis data of the National Centers for Environmental Prediction (NCEP)/Nation al Center for Atmospheric Research (NCAR). Both the axial AAM functions agr ee well in annual variation and roughly in semiannual variation! with the f unction inferred from the observed LOD. The two equatorial AAM functions sh ow the different wind contributions to the function inferred from the obser ved wobble. in both annual and semiannual variations, which are attributabl e in part to the different vertical wind integration methods between NCEP/N CAR and JMA. The equatorial tropospheric wind contributions, calculated by the same method; are found to show discrepancies arising from the different tropospheric regional winds associated with the Asian monsoon.