High Accuracy Earth Rotation and Atmospheric Angular Momemtum

Abstract

Recent advances in the measurement and interpretation of Earth rotation and polar motion are highlighted here, focusing on short period fluctuations and their relation with changes in the global atmospheric angular momentum (AAM). Particular emphasis and attention are placed on data acquired during the MERIT campaign (September 1983 — October 1984). The modern space geodetic techniques have achieved unprecented accuracy and precision; intercomparisons of the recent MERIT results indicate that Earth orientation is currently determined with an accuracy of ~ 5 cm. High-quality estimates of the atmospheric excitation of Earth rotation and polar motion are provided by the routine analysis of global weather data for operational weather forecasting. Fluctuations in Earth rotation over the time scale of a year or less are dominated by atmospheric effects; the agreement between changes in length of day (LOD) and AAM estimates is striking. In contrast, comparisons between geodetic and meteorological estimates of the excitation of the polar motion are as yet not as satisfactory, indicating the presence of challenging “Vinsolved problems.” The presence of rapid high frequency fluctuations in the polar motion excitation pressure term is noted, these are marginally detectable by the modern geodetic techniques.