Abstract
Recent satellite data and modeling studies indicate a pronounced role Tropical Instability Waves (TIW)-induced wind feedback plays in the tropical Pacific climate system. Previously, remotely sensed data were used to derive a diagnostic model for TIW-induced wind stress perturbations (τTIW), which was embedded into an ocean general circulation model (OGCM) to take into account TIW-induced ocean-atmosphere coupling in the tropical Pacific. While the previous paper by Zhang (2013) is concerned with the effect on the mean ocean state, the present paper is devoted to using the embedded system to examine the effects on TIW activity in the ocean, with τTIW being interactively determined from TIW-scale sea surface temperature (SSTTIW) fields generated in the OGCM, written as τTIW = αTIW·F(SSTTIW), where αTIW is a scalar parameter introduced to represent the τTIW forcing intensity. Sensitivity experiments with varying αTIW (representing TIW-scale wind feedback strength) are performed to illustrate a negative feedback induced by TIW-scale air-sea coupling and its relationship with TIW variability in the ocean. Consistent with previous modeling studies, TIW wind feedback tends to have a damping effect on TIWs in the ocean, with a general inverse relationship between the τTIW intensity and TIWs. It is further shown that TIW-scale coupling does not vary linearly with αTIW: the coupling increases linearly with intensifying τTIW forcing at low values of αTIW (in a weak τTIW forcing regime); it becomes saturated at a certain value of αTIW; it decreases when αTIW goes above a threshold value as the τTIW forcing increases further. This work presents a clear demonstration of using satellite data to effectively represent TIW-scale wind feedback and its multi-scale interactions with large-scale ocean processes in the tropical Pacific.
Highlights
Tropical instability waves (TIWs) are intraseasonal, small-scale phenomena in the central-eastern tropical Pacific which were first revealed from remotely sensed image [1]
Surface winds are a dominant one affecting TIW activity on seasonal and interannual time scales in the tropical Pacific
TIW activity can be affected by TIW-scale wind forcing itself, as revealed by recent satellite observations and modeling studies
Summary
Tropical instability waves (TIWs) are intraseasonal, small-scale phenomena in the central-eastern tropical Pacific which were first revealed from remotely sensed image [1]. Without making use of a comprehensive atmospheric model that can resolve TIW variability in a computationally intensive way, this embedded modeling system allows one to decipher the impact of TIW-induced wind feedback on the ocean, and further its interactions with seasonal and interannual variations over the tropical Pacific. Small et al [23] illustrated another negative feedback involved with ocean current-induced effects on surface wind stress using a regionally fully coupled ocean-atmosphere model over the eastern tropical Pacific. While a fully coupled ocean-atmosphere model with high resolution can be used to depict TIW-scale wind variability in the region [20,27,28,29], it is difficult to unambiguously isolate TIW-induced feedback effects since all related multi-scale processes are present together, with their effects intermingled.
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