Abstract
THE El Nino 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 system1. 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 Nino and related La Nina climatic events occur when these components add constructively.
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