Nature 357, 484 - 488 (11 June 1992); doi:10.1038/357484a0

Global propagation of interannual fluctuations in atmospheric angular momentum

J. O. Dickey^*, S. L. Marcus^* & R. Hide^†

^* Space Geodetic Science and Applications Group, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA
^† Meteorological Office Unit, Robert Hooke Institute, The Observatory, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK

THE El Niño Southern Oscillation (ENSO), a climate fluctuation that recurs on a 2–7-yr timescale, is associated with persistent large-scale fluctuations in the dynamical behaviour of the global atmosphere–ocean system^1. Here we present a study of the latitudinal redistribution of angular momentum within the atmosphere from 1976 to 1991. We observe slow, global-scale coherent poleward propagation of atmospheric angular-momentum fluctuations on interannual timescales. These originate in equatorial regions, where they lead the main atmospheric anomalies of the ENSO cycle by nearly two years; they penetrate to latitudes higher than 60° in both hemispheres, where they lag behind the ENSO cycle by about four years. We can also distinguish the bimodality of the ENSO phenomenon, with a low-frequency component centred at a period close to 4.2 years and a high-frequency component centred near 2.4 years. Each of the two components has a distinct latitudinal propagation pattern. In the period studied, strong El Niño and related La Niña climatic events occur when these components add constructively.

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