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Mitigating climate biases in the midlatitude North Atlantic by increasing model resolution: SST gradients and their relation to blocking and the jet

Athanasiadis, Panos J. and Ogawa, Fumiaki and Omrani, Nour-Eddine and Keenlyside, Noel and Schiemann, Reinhard and Baker, Alexander J. and Vidale, Pier Luigi and Bellucci, Alessio and Ruggieri, Paolo and Haarsma, Rein and Roberts, Malcolm and Roberts, Chris and Novak, Lenka and Gualdi, Silvio (2022) Mitigating climate biases in the midlatitude North Atlantic by increasing model resolution: SST gradients and their relation to blocking and the jet. Journal of Climate, 35 (21). pp. 3385-3406. ISSN 0894-8755. doi:10.1175/jcli-d-21-0515.1.

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Starting to resolve the oceanic mesoscale in climate models is a step change in model fidelity. This study examines how certain obstinate biases in the midlatitude North Atlantic respond to increasing resolution (from 1° to 0.25° in the ocean) and how such biases in sea surface temperature (SST) affect the atmosphere. Using a multi-model ensemble of historical climate simulations run at different horizontal resolutions, it is shown that a severe cold SST bias in the central North Atlantic, common to many ocean models, is significantly reduced with increasing resolution. The associated bias in the time-mean meridional SST gradient is shown to relate to a positive bias in low-level baroclinicity, while the cold SST bias causes biases also in static stability and diabatic heating in the interior of the atmosphere. The changes in baroclinicity and diabatic heating brought by increasing resolution lead to improvements in European blocking and eddy-driven jet variability. Across the multi-model ensemble a clear relationship is found between the climatological meridional SST gradients in the broader Gulf Stream Extension area and two aspects of the atmospheric circulation: the frequency of high-latitude blocking and the southern-jet regime. This relationship is thought to reflect the two-way interaction (with a positive feedback) between the respective oceanic and atmospheric anomalies. These North Atlantic SST anomalies are shown to be important in forcing significant responses in the midlatitude atmospheric circulation, including jet variability and the stormtrack. Further increases in oceanic and atmospheric resolution are expected to lead to additional improvements in the representation of Euro-Atlantic climate.

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Novak, Lenka0000-0003-0561-3458
Additional Information:PJA and AB acknowledge funding from the PRIMAVERA project, funded by the European Union’s Horizon 2020 programme under Grant Agreement 641727. MR acknowledges support from the Joint U.K. BEIS/Defra Met Office Hadley Centre Climate Programme (Grant GA01101). N-E. Omrani was supported by 1) the Bjerknes Climate Prediction Unit with funding from the Trond Mohn Foundation (Grant BFS2018TMT01) and 2) the RCN-funded ROADMAP project (316618) under a joint JPI Climate and JPI Ocean call. PA acknowledges funding also from the Italian Ministry of Education, University and Research (MIUR) through the JPI Oceans and JPI Climate “Next Generation Climate Science in Europe for Oceans” ROADMAP Project (D.M. 593/2016). Finally, the authors thank three anonymous reviewers for their comments and suggestions that greatly improved the original manuscript. Data availability statement. All data from PRIMAVERA HighResMIP simulations used in this study are available from the Earth System Grid Federation (ESGF). ERA5, ERA-40, and ERA-Interim reanalysis data are available from the European Centre for Medium Range Weather Forecasting (ECMWF). The HadISST2 high-resolution SST data used (1950–2014) are available from the ESGF ( The OAFlux data used in this study are available from the Research Data Archive of the National Center for Atmospheric Research (NCAR;
Funding AgencyGrant Number
European Research Council (ERC)641727
Meteorological Office (UK)GA01101
Trond Mohn FoundationBFS2018TMT01
Research Council of Norway316618
Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR)593/2016
Issue or Number:21
Record Number:CaltechAUTHORS:20221121-712406200.21
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117956
Deposited By: Research Services Depository
Deposited On:02 Dec 2022 18:39
Last Modified:02 Dec 2022 18:39

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