A seasonal budget of the Earth's axial angular momentum

Abstract

The seasonal variation of the earth's axial angular momentum budget is discussed with an error on the order of a few percent. The budget is based on the core‐mantle decoupling (CMD) hypothesis, using the length of day (LOD) data observed astronomically by the International Radio Interferometry Surveying and the atmospheric angular momentum data calculated from the forecast/analysis data set for numerical weather prediction of the Japan Meteorological Agency. The atmospheric relative angular momentum changes due to zonal wind account for an additional 23 % contribution over the annual budget. However, this is counterbalanced by the effects of the redistributions of air and water masses. Namely, about 16 % is accounted for by the redistribution of air mass, and remained about 7 % agrees with the contribution from surface water storage estimate on continents by Chao & O'Connor [1988]. These facts demonstrate a confirmation of the CMD hypothesis on time scale of a year. At the semi‐annual period, however, there still is a shortage of about 6 % in atmospheric and hydrospheric contributions to the budget.