A Study On The Parameterization Of Mesoscale Wind Stress Induced Feedback Effect And Its Role In Reducing The Simulated SST Warm Bias In The Western Coast Of South America

The interaction between the mesoscale perturbations of sea surface temperature(SST_meso)and wind stress(WS_meso)has great influences on the ocean and atmosphere.However,most current climate models cannot adequately capture the characteristics of mesoscale wind stress-SST coupling.In the in the western coast of South America with strong mesoscale coupling,there is a consistent warm SST bias in most of climate model simulations.Using daily Quik-SCAT wind data and AMSR-E SST data,SST_meso and WS_mesofields in the western coast of South America are extracted by using a locally weighted regression method(LOESS).The spatial patterns of SST_meso and WS_meso indicate strong mesoscale SST-wind stress coupling in the region.The least-squares regression analysis is used to calculate the mesoscale air-sea coupling coefficient in the sea area,and it is found that the mesoscale coupling in the sea area has obvious seasonal changes.The coupling coefficient between SST_meso and WS_meso is about 0.0095 N·m^-2/°C in winter and 0.0082 N·m^-2/°C in summer.Based on mesoscale coupling relationships,we build a parameterized method for the mesoscale wind stress induced feedback effect.The mesoscale perturbations of wind stress divergence and curl can be obtained from the SST gradient perturbations,which can be further used to derive wind stress vector perturbations using the Tikhonov regularization method.The computational examples are presented in the western coast of South America.By matching the spatially averaged maximum standard deviations of reconstructed WS_meso magnitude and observations,a reasonable magnitude of WS_meso can be obtained when the rescaling factor is used.This parameterized method is used in Regional Oceanic Modelling Systems(ROMS)and can be used to represent mesoscale wind stress–SST coupling.It is found that SST can be cooled down in the western coast of South America if the feedback effect of mesoscale coupling is included in the numerical simulaitons.The reduced maximum value of SST can reach 0.3?in the Peru sea and 0.7?in the Chile sea.The mixed layer(ML)heat budget analysis indicates that horizontal advection,vertical heat diffusion and surface heat flux are the main terms that explain the change in SST.The SST changes in Chile sea and Peru are dominated by horizontal advection and vertical diffusion,respectivly.Furthermore,the mesoscale coupling can lead to a strengthened vertical velocity which is mainly controlled by the Ekman pumping induced by WS_meso.The strengthened Ekman pumping acts to bring subsurface cold water to the sea surface,leading to a cooling of SST.Additionally,SST change is damped via surface heat flux adjustment.Analyses of the sensitivity experiments demonstrate that SST change in the momentum feedback experiment occurs both in the sea of Peru and Chile,while SST change in the thermal feedback experiment mainly occurs in the Chile sea.The SST difference between the mesoscale coupling experiment and control experiment is generally a sum of the SST differences between the two sensitivity experiments and control experiment.The feedback induced by mesoscale coupling is also studied in a large-scale coupled model.The results indicate the cooling effect of SST can be strengthened in the large-scale coupled ocean-atmosphere model.The reduced maximum value of SST can reach 0.4?in the Peru sea and 0.8?in the Chile sea.The horizontal advection,vertical heat diffusion and surface heat flux are still the main terms that explain the change in SST.The empirical wind stress perturbation model developed in this study can be used to improve the simulation of mesoscale coupling in the ocean model and climate model.