Pinpointing sources of equatorial Pacific climatological SST biases in a coupled GCM via surface flux adjustments

Pinpointing sources of equatorial Pacific climatological SST biases in a coupled GCM via surface flux adjustments | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 15 May 2025 V1 Latest version Share on Pinpointing sources of equatorial Pacific climatological SST biases in a coupled GCM via surface flux adjustments Authors : Xian Wu 0000-0001-8117-6603 [email protected] , Andrew T. Wittenberg 0000-0003-1680-8963 , Fanrong Zeng 0000-0001-6212-7187 , Brandon G Reichl 0000-0001-9047-0767 , and Feiyu Lu 0000-0001-6532-0740 Authors Info & Affiliations https://doi.org/10.22541/au.174733523.37826607/v1 415 views 232 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Global weather and climate forecasts hinge on the ability of coupled general circulation models (CGCMs) to simulate the powerful ocean-atmosphere interactions in the tropical Pacific. Yet most CGCMs develop tropical Pacific biases, such as an overly-intense equatorial cold tongue (ECT), which limit their simulation skill. Here we illuminate the sources of these biases in the GFDL SPEAR global CGCM, using bias-corrected simulations with surface nudging or flux adjustments. We find that the CGCM biases stem from (1) the atmosphere component’s excessive convective rainfall, which accelerates the equatorial trade winds; (2) the ocean component’s insufficient near-surface vertical mixing, which shoals the tropical mixed layers and ECT thermocline; and (3) the ocean component’s insufficient tropical instability wave (TIW) stirring, especially during August-November and La Niña, which weakens the meridional convergence of surface heat into the ECT. In the CGCM, coupled feedbacks further intensify and westward-displace the equatorial cold tongue, rainfall, trade winds, surface currents, Ekman upwelling, and thermocline tilt. This then reduces the cross-equatorial asymmetry of the east Pacific climatology, resulting in an overly semiannual cycle of equatorial SST; and intensifies TIW-driven heating of the ECT, counteracting the TIW attenuation in the coarse-gridded ocean model. The CGCM’s excessive ECT heat uptake is compensated by weaker evaporation, while its insufficient western equatorial Pacific heat uptake is compensated by stronger evaporation and cloud shading. We highlight avenues to improve SPEAR and other CGCMs, via improved process representation informed by enhanced observations of the tropical Pacific upper-ocean heat budget and air-sea coupling. Supplementary Material File (1033301_0_merged_1746492825.pdf) Download 20.50 MB File (fa_meanstate_supplemental_submit.pdf) Download 8.68 MB Information & Authors Information Version history V1 Version 1 15 May 2025 Copyright This work is licensed under a Creative Commons Attribution 4.0 International License Keywords air-sea interaction climate modeling cold tongue bias enso tropical instability waves tropical rainfall Authors Affiliations Xian Wu 0000-0001-8117-6603 [email protected] The University of Texas at Dallas View all articles by this author Andrew T. Wittenberg 0000-0003-1680-8963 NOAA Geophysical Fluid Dynamics Laboratory View all articles by this author Fanrong Zeng 0000-0001-6212-7187 GFDL View all articles by this author Brandon G Reichl 0000-0001-9047-0767 NOAA Geophysical Fluid Dynamics Laboratory View all articles by this author Feiyu Lu 0000-0001-6532-0740 NOAA Geophysical Fluid Dynamics Laboratory View all articles by this author Metrics & Citations Metrics Article Usage 415 views 232 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Xian Wu, Andrew T. Wittenberg, Fanrong Zeng, et al. Pinpointing sources of equatorial Pacific climatological SST biases in a coupled GCM via surface flux adjustments. Authorea . 15 May 2025. DOI: https://doi.org/10.22541/au.174733523.37826607/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. 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