Evaporation-wind feedback and low-frequency variability in the tropical atmosphere

J. David Neelin, Isaac M. Held, and Kerry H. Cook
J. Atmos. Sci., 44, 2341-2348, 1987. Paper (PDF 743KB)
© Copyright 1987 by the American Meteorological Society.

Abstract. A mechanism by which feedback between zonal wind perturbations and evaporation can create unstable, low-frequency modes in a simple two-layer model of the tropical troposphere is presented. The modes resemble the 30-50 day oscillation. A series of general circulation model experiments designed to test the effect of suppressing this feedback on low-frequency variability in the model tropics is described. The results suggest that the evaporation-wind feedback can be important to the amplitude of the spectral peak corresponding to the 30-50 day oscillation in the model, but that the existence of the oscillation does not depend on it. The feedback is found to have a much more dramatic effect on low- frequencey variability when sea surface temperatures are fixed than when the lower boundary is a zero heat capacity "swamp".

Citation. Neelin, J. D., I. M. Held and K. H. Cook, 1987: Evaporation-wind feedback and low frequency variability in the tropical atmosphere. J. Atmos. Sci., 44, 2341-2348.

Acknowledgments. We are especially grateful to N. C. Lau and T. R. Knutson for access to unpublished diagnostics of the low-frequency variability of the GCM. We also thank N. C. Lau and B. Wang for helpful comments on the manuscript and R. T. Pierrehumbert and Y. Hayashi for useful discussions. One of the authors (JDN) was supported by a postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada.

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