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Zhengyu Liu


A simple theoretical analysis identified three possible interannual positive feedbacks in the extratropics: the upwelling mode, the SST-Sverdrup mode, and the SST-evaporation mode. The upwelling mode becomes unstable when the atmosphere responses to a warm SST anomaly predominantly with a high surface pressure. In contrast, the SST-Sverdrup mode is destabilized when the atmosphere responses to a warm SST with a low pressure. In the region of mean westerly wind, the SST-evaporation mode is unstable when the atmospheric response to a warm SST is a qurater-wavelength to the south. The upwelling mode seems to favor low-latitude regions, while the two SST modes seem to favor midhigh latitudes. It is suggested that the relative position of the stationary atmospheric response to anomalous SST is of crucial importance for the extratropical ocean-atmosphere interaction.

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Zhengyu Liu and Shangping Xie


A simple coupled ocean–atmospheric boundary layer model is used to study the annual variability in the eastern tropical Pacific. The air–sea coupling, particularly the feedback of the total wind speed effect on evaporation and wind mixing entrainment, produces a rapid equatorward and westward propagation of annual disturbances. For reasonable parameters, both amplitude and phase of the annual disturbance can be reproduced fairly well over most of the Tropics. It is then suggested that a substantial part of equatorial annual variability may come from the extratropics (say beyond 15°) due to the propagation of coupled waves.

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