The ocean reveals the important role of the vertical mixing process in the formation of subsurface model errors


Based on the ocean Model Comparison Project (OMIP) data, we conducted an improved study on the estimation of temperature errors in the tropical Atlantic subsurface layer. The results were published in The Journal of Climate.Climate model is an important tool to study climate and its changes.Since the establishment of the air-sea coupling model based on mathematical equations in the 1960s, significant achievements have been made in the development and application of climate models.For example, it can reproduce global warming caused by the increase of greenhouse gases in the atmosphere;In 2021, the sixth International Coupled Model Comparison Program (CMIP6) will be released. These model-based simulations are the main basis for IPCC (Intergovernmental Panel on Climate Change) and other assessments of future climate change.However, there are significant differences and uncertainties between climate model simulation results and observations, and these systematic errors weaken the reliability of model climate prediction and future projections.Attribution of error and improvement of pattern performance are hot and difficult issues in pattern development, and also one of the scientific issues concerned by CMIP6.In the past, researches on climate model errors were mostly confined to the sea surface errors, and little attention was paid to the simulation of the ocean subsurface.Using newly published OMIP data, we found that there is a basin-scale warming error in the tropical Atlantic sub-surface.The error mainly occurs in the subsurface sea area of 100-150 m, and there are two warm error centers outside the equator.Compared with the south side error, the north side error has stronger intensity and deeper depth.As a typical characteristic of systematic error in OMIP model, this error has no obvious seasonal variation.Furthermore, this study explores the causes of this error from both atmospheric and oceanic aspects by conducting sensitivity tests of a separate ocean model.From the atmospheric point of view, this error can be partly attributed to the uncertainty of the model stroke field.From the perspective of the ocean, this error is mainly due to the uncertainty of the upper ocean vertical mixing parameterization scheme.Compared with turbulent microscale observations, the ocean model overestimates the intensity of internal vertical mixing.By replacing the values given in existing models with diffusion coefficients estimated by observations, stratification is strengthened and the tropical Atlantic subsurface simulation is significantly improved, reducing the subsurface warming error by about 50%.Further heat budget analysis shows that the improvement of subsurface SST simulation is mainly due to the enhancement of vertical mixed cooling.In addition, due to the improvement of the subsurface thermal structure modeling, the simulation of tropical current system has also been improved correspondingly, including more realistic simulations such as the strengthening of the NORTH Equatorial current.This study reveals the important role of ocean vertical mixing process in the formation of subsurface model errors, which is of great significance for improving the simulation and prediction ability of ocean and climate numerical models, and provides theoretical guidance for improving climate models.The research work is supported by the Marine Science Research Center of CAS, Qingdao Pilot National Laboratory for Marine Science and Technology, Cas Center for Excellence and Innovation in Quaternary Science and Global Change, CAS Strategic Priority Project and National Natural Science Foundation of China.The tropical Atlantic sub-surface temperature error (& GT;3℃) spatial structure and attribution diagram.Among them, the surface is the wind stress curl error of OMIP model ensemble average (unit: 10-8 N m-3), and the sub-surface shows the THREE-DIMENSIONAL temperature error of OMIP model ensemble average (unit: ℃) and its projection on the longitudinal-latitude plane and depth-latitude plane.Disclaimer: This article is reproduced for the purpose of conveying more information.If the source is wrong or violated your legitimate rights and interests, please contact the author with proof of ownership, we will promptly correct, delete, thank you.Email address: newmedia@xxcb.cn

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