METEOROLOGICAL EXCITATION OF INTERANNUAL POLAR MOTION BY THE NORTH-ATLANTIC OSCILLATION

Variations of the atmospheric angular momentum (AAM) is responsible fo r almost all of the observed length-of-day (LOD) variation on time sca les from several days to several years, and much of the observed polar motion on the intra-seasonal time scale. El Nino/Southern Oscillation (ENSO) and Quasi-Biennial Oscillation (QBO) have been singled out to successfully explain interannual LOD variations. However, excitation s ources for the interannual polar motion, including the 14 month Chandl er wobble, have not been positively identified. This paper studies the correlation of the observed polar motion Psi with the North Atlantic Oscillation (NAO), an interannual, mid-latitude, north-south seesaw in the atmosphere-ocean system. An index (NAOI) used as a proxy to measu re the strength of NAO is compared with the observed interannual polar motion excitation during 1964-1994. Cross-correlation functions and c oherence spectra demonstrate significant correlations between NAOI and Psi, especially in the x component as expected from NAO's location an d general pattern. This constitutes: a positive identification of exci tation of interannual polar motion by a meteorological system. Further more, our corresponding results with respect to ENSO strongly suggest that a combination of meteorological systems will better explain the o bserved interannual polar motion and perhaps the Chandler wobble. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.