Meteorological excitation of interannual polar motion by the North Atlantic Oscillation

Variations of the atmospheric angular momentum "AAM# is responsible for almost all of the observed length!of!day "LOD# variation on time scales from several days to several years\ and much of the observed polar motion on the intra!seasonal time scale[ El Nin1⁄2o:Southern Oscillation "ENSO# and Quasi!Biennial Oscillation "QBO# have been singled out to successfully explain interannual LOD variations[ However\ excitation sources for the interannual polar motion\ including the 03 month Chandler wobble\ have not been positively identi_ed[ This paper studies the correlation of the observed polar motion C 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 measure the strength of NAO is compared with the observed interannual polar motion excitation during 0853Ð0883[ Cross!correlation functions and coherence spectra demonstrate signi_cant correlations between NAOI and C\ especially in the x component as expected from NAO|s location and general pattern[ This constitutes a positive identi_cation of excitation of interannual polar motion by a meteorological system[ Furthermore\ our corresponding results with respect to ENSO strongly suggest that a combination of meteorological systems will better explain the observed interannual polar motion and perhaps the Chandler wobble[ Þ 0887 Published by Elsevier Science Ltd[ All rights reserved