Slowly Propagating Disturbances in a Coupled Ocean-Atmosphere Model

David L. T. Anderson Department of Atmospheric Physics, Clarendon Laboratory, Oxford OXI 3PU, England

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Julian P. McCreary Nova University Oceanographic Center, Dania, FL 33004

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Abstract

Solutions to a coupled atmosphere model are discussed. The model ocean is a generalization of a reduced-gravity model that includes an equation for the temperature of the layer T. The model atmosphere is linear, baroclinic, and assumed to be in equilibrium with a forcing that represents the release of latent heal by convection Q. The wind stress τ used to drive the ocean is proportional to the wind velocity produced by the model atmosphere, while Q over the ocean is a function only of sea surface temperature. Some of the solutions involve land is well as ocean; in that case Q over land is specified externally and is not influenced by ocean temperature.

The atmosphere is always cyclic in longitude, but three different ocean-land configurations are considered: a) a zonally unbounded, cyclic ocean with no land; b) a bounded ocean with convection over land strong to the west; and c) a bounded ocean with convection over land strong to the cast. Case. b resembles the situation in the Pacific Ocean, with the strong land convection to the west representing the convection over Indonesia, whereas case c resembles the situation in the Indian Ocean. Eastward propagating large-amplitude oscillations develop in cases a and b. They are associated with warm-water pools that have a scale comparable with that observed during the 1982-83 El Nino event, but their propagation speed is only half that observed. No oscillations occur in case c, suggesting that Indonesian convection lion a fundamentally different effect on the Indian and Pacific Oceans.

Abstract

Solutions to a coupled atmosphere model are discussed. The model ocean is a generalization of a reduced-gravity model that includes an equation for the temperature of the layer T. The model atmosphere is linear, baroclinic, and assumed to be in equilibrium with a forcing that represents the release of latent heal by convection Q. The wind stress τ used to drive the ocean is proportional to the wind velocity produced by the model atmosphere, while Q over the ocean is a function only of sea surface temperature. Some of the solutions involve land is well as ocean; in that case Q over land is specified externally and is not influenced by ocean temperature.

The atmosphere is always cyclic in longitude, but three different ocean-land configurations are considered: a) a zonally unbounded, cyclic ocean with no land; b) a bounded ocean with convection over land strong to the west; and c) a bounded ocean with convection over land strong to the cast. Case. b resembles the situation in the Pacific Ocean, with the strong land convection to the west representing the convection over Indonesia, whereas case c resembles the situation in the Indian Ocean. Eastward propagating large-amplitude oscillations develop in cases a and b. They are associated with warm-water pools that have a scale comparable with that observed during the 1982-83 El Nino event, but their propagation speed is only half that observed. No oscillations occur in case c, suggesting that Indonesian convection lion a fundamentally different effect on the Indian and Pacific Oceans.

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