Coupled Processes and the Tropical Climatology. Part III: Instabilities of the Fully Coupled Climatology

Henk A. Dijkstra and J. David Neelin
J. Climate, 12, 1630-1643.

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© Copyright 1999 by the American Meteorological Society.

Coupled processes between the equatorial ocean and atmosphere control the spatial structure of the annual-mean state in the Pacific region, in particular the warm pool-cold tongue structure. At the same time, coupled processes are known to be responsible for the variability about this mean state, in particular the El Niño-Southern Oscillation phenomenon. In this paper, the connection between both effects of coupling is considered by investigating the linear stability of fully coupled climatologies in an intermediate coupled model. The new element here is that when parameters such as the coupling strength are changed, the potential amplification of disturbances can be greatly influenced by a simultaneous modification of the mean state. This alters the stability properties of the coupled climatology, relative to the flux-corrected cases that have been previously studied. It appears possible to identify a regime in parameter space where ENSO-like unstable modes coincide with a reasonable warm pool-cold tongue structure. These unstable modes are mixed SST-ocean dynamics modes, that is, they arise through an interaction of oscillatory modes originating from ocean dynamics and oscillatory SST modes. These effects are qualitatively similar in this fully coupled problem compared to the flux-corrected problem, but the sensitivity of the ENSO mode to parameters and external variations is larger due to feedbacks in the climatology.

Citation. Dijkstra, H. A., and J. D. Neelin, 1999: Coupled processes and the tropical climatology. Part III: Instabilities of the fully coupled climatology. J. Climate, 12, 1630-1643.

Acknowledgments. The work of HD was supported by the Dutch National Research Programme on Global Air Pollution and Climate Change (N.R.P.) within Project 951235. All computations were performed on the CRAY C90 at the Academic Computing Centre (SARA), Amsterdam, the Netherlands, within Project SC283. Use of these computing facilities was sponsored by the National Computing Facilities Foundation (N.C.F.) with financial support from the Netherlands Organization for Scientific Research (N.W.O). This work was initiated and completed during visits of HD to UCLA in 1993, 1996, and 1997 and sponsored by NSF Grant ATM-9521389 and a N.W.O. PIONIER grant. Discussions with Fei-Fei Jin are much appreciated.
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