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Abstract

Tropical instability waves (TIWs) are the dominant mesoscale variability in the eastern equatorial Pacific Ocean.TIWs have direct impacts on the local hydrology, biochemistry and atmospheric boundary layer, and feedback on ocean circulations and climate variability.In this study, the basic characteristics of Pacific Ocean TIWs simulated by an eddy-resolving ocean model and a coupled general circulation model are evaluated.The simulated TIW biases mainly result from the mean climatology state.Both the oceanic and coupled models reproduce the observed westward propagating large-scale Rossby waves between approximately 2◦–8◦N, but the simulated TIWs have shorter wavelengths than the observed waves due to the shallower thermocline.Meanwhile, the weak meridional shears of background zonal currents and the less-tilted pycnocline in these two models compared to the observations causes weak barotropic and baroclinic instability, which decreases its intensity.We then identify the roles of atmospheric feedback in modulating TIWs.The latent heat flux feedback is similar to observation in the coupled model but absent in the ocean model, contributing to the stronger standard deviation of the TIW SST in the ocean model.The ocean model is not able to capture realistic air–sea interaction processes when forced with prescribed atmospheric forcing.However, the misrepresented atmospheric feedback in the ocean model tends to decrease the SSH variability, and the current feedback damping effect is stronger in the ocean model than in the coupled model.Combined with weaker barotropic and baroclinic conversion rate in the ocean model than in the coupled model, the STD of the TIW SSH in the ocean model is weaker.