The Bimodal Tropical Instability Waves-Induced Air-Sea Interaction In The Pacific And Its Representations In The Models

Tropical Instability Waves(TIWs)in the Pacific Ocean are the typical mesoscale intraseasonal processes occurring near the equatorial eastern Pacific Ocean.Mesoscale processes are usually accompanied by strong air-sea interactions,and the coupling relationship between the wind stress perturbations and sea surface temperature(SST)perturbation induced by TIWs has been revealed.On the one hand,there is a clear linear relationship between the TIW-induced SST perturbations and the wind stress perturbations;on the other hand,there is also a clear linear relationship between the divergence(curl)of the TIW-induced wind stress perturbations and the gradients of SST perturbations gradients in downwind and cross wind directions.On the other hand,there is also an obvious linear relationship between the divergence and curl of the wind stress perturbations induced by TIWs and the gradient of SST perturbations in downwind and crosswind directions.However,previous studies have overlooked the fact that the generalized definition of "TIWs" actually includes two modes,including Yanai wave-based TIWs on the equator(hereafter referred to as e TIW)and Rossby wave-based TIWs off the equator(hereafter referred to as v TIW).Hence the individual feedbacks of the wind stress to the bimodal TIWs remain unexplored.Therefore,in this study,based on previous studies on the generalized definition of TIWs,the air-sea coupling relationships induced by e TIW and v TIW are established.The relationships include(1)the relationships between the SST perturbations induced by TIWs and the longitudinal-latitudinal components of wind stress perturbations,as well as(2)the relationships between the divergence(curl)of wind stress perturbations and the downwind(crosswind)SST gradients induced by bimodal TIWs.Due to the different distributions of e TIW and v TIW,we find that the air-sea coupling intensity induced by e TIW is stronger at the equator,while the coupling intensity due to v TIW is stronger off the equator.Any of the coupling relationships we establish for e TIW and v TIW are more specific,and they are stronger than those established of the loosely defined ‘TIW’are.The lack of observations and the shortcomings of most current numerical models,in particular,the air-sea interactions in numerical simulations are often weaker than those in actual observations,which underestimate the impact of TIWs on the ocean to some extent and limit the in-depth study of them.Therefore,we evaluate some current widely accepted ocean circulation models and fully coupled climate models,using the air-sea interaction models obtained from the observations to quantify the air-sea coupling relationships in the models.It is found that these coupling relationships are not well represented in most numerical models,and the bimodal TIW-induced SST perturbations and wind stress perturbations cannot be well reproduced in some models.In addition,during the study,we also find that the higher the resolution,the better the reproduction of these air-sea coupling relations,while other conditions are kept constant.Therefore,the coupled model established in this paper can fill the gaps in previous studies and can be used to improve the ocean and coupled climate models,improving the simulation of bimodal TIWs and their induced air-sea interactions in the ocean models and the fully coupled climate models,providing a way to improve the forecasting of ENSO.