Atmospheric angular momentum fluctuations and their excitations of earth rotation variations at seasonal scale

We discuss the atmospheric contributions, especially wind contribution, to seasonal variations in the polar wobble and length of day during the period 1985–1995. The atmospheric angular momentum functions, calculated from the output data of GSM9603 GCM of Japan Meteorological Agency (JMA) are compared with those calculated from the reanalysis data of NCEP / NCAR, and from the operational objective analysis data of JMA. The results show that two different vertical wind integration methods lead to different wind contributions to seasonal polar wobble, especially for the component along Greenwich meridian direction in annual variation. However the inter-annual variations of wind contributions estimated by these two methods are almost the same with each other in the two equatorial components. The simulated axial relative AAM function agrees well with the other two as regards the seasonal variation. In addition, its inter-annual amplitude fluctuation of axial relative AAM function at semi-annual scale shows the main characteristics of ENSO evolution better than that estimated from the NCEP reanalysis data, that is, the semi-annual axial relative AAM oscillation becomes weaker during ENSO periods.