Ocean-Atmosphere Interaction and the Tropical Climatology, Part I: The dangers of flux corrections.

Henk A. Dijkstra and J. David Neelin
J. Climate, 8, 1325-1342, 1995.

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© Copyright 1995 by the American Meteorological Society.

Abstract. In this sequence of papers, we study the role of dynamical feedbacks between ocean and atmosphere in determining features of the tropical climatology. A stripped-down intermediate coupled ocean-atmosphere model is used to provide a prototype problem for the Pacific basin. Here we contrast the fully coupled case with the case where flux correction is used to construct the climatology. In the fully coupled case, the climatology is determined largely by feedback mechanisms within the ocean basin: winds driven by gradients of sea surface temperature (SST) within the basin interact with the ocean circulation to maintain SST gradients. For all realistic cases, these lead to a unique steady solution for the tropical climatology. In the flux-corrected case, the artificially constructed climatology becomes unstable at sufficiently large coupling, leading to multiple steady states as found in a number of coupled models. Using continuation methods, we show that there is a topological change in the bifurcation structure as flux-correction is relaxed towards a fully coupled case; this change is characterized as an imperfection and must occur generically for all flux-corrected cases. The cold branch of steady solutions is governed by mechanisms similar to the fully coupled case. The warm branch, however, is spurious and disappears. The dynamics of this and consequences for coupled models are discussed. Multiple steady states can be ruled out as a mechanism for El Ni\~no, in favor of oscillatory mechanisms. We refer to important role coupled feedbacks are suggested to play in establishing tropical climatology as ``the climatological version of the Bjerknes hypothesis''.

Citation. Neelin, J. D. and H. A. Dijkstra, 1995: Ocean-atmosphere interaction and the tropical climatology. Part I: The dangers of flux correction. J. Climate, 8, 1325-1342.

Acknowledgments. This work was supported in part by National Science Foundation grant ATM-9215090 and NOP-project 853110. All computations were performed on the CRAY Y-MP at the Academic Computer Centre (SARA), Amsterdam, the Netherlands, with financial support from Netherlands Organization for Scientific Research (NWO).

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