Externally forced circulation changes amplify mid-latitude regional heat extremes in climate model nudged-circulation experiments

Externally forced circulation changes amplify mid-latitude regional heat extremes in climate model nudged-circulation experiments | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Externally forced circulation changes amplify mid-latitude regional heat extremes in climate model nudged-circulation experiments Jitendra Singh, Sebastian Sippel, Lei Gu, Reto Knutti, Erich Fischer This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7299009/v2 This work is licensed under a CC BY 4.0 License Status: Posted Version 2 posted You are reading this latest preprint version Show more versions Abstract Large-scale atmospheric circulation changes have strongly modulated the frequency and intensity of regional heat extremes in the NH mid-latitudes over recent decades. But whether these changes are due to external forcing or internal variability remains unclear. This challenge arises from the intertwined nature of thermodynamic and dynamic responses to climate forcing. We present an atmospheric circulation-constrained framework using the CESM2 model to quantify externally forced dynamic and thermodynamic contributions to seasonal surface temperature and heat extremes. We show that, depending on the region, a substantial portion of circulation-driven changes in boreal summer average temperature and heat extremes is externally forced, with distinct regional patterns. Forced circulation changes have amplified summer heat extremes by up to 1°C since 1979 in several northern mid-latitude regions, including the Pacific Northwest, Central Europe, South Siberia, and North China/Mongolia. These signals coincide with persistent high-pressure anomalies and enhanced mid-tropospheric ridging, consistent with increased atmospheric blocking. In contrast, forced circulation changes have contributed to regional cooling in parts of the northeastern United States, central Africa, and East Asia. With a physically consistent way to constrain feedback and isolate externally forced circulation signals from internal variability, this new framework offers critical insights into reducing uncertainties in the attribution and projection of regional climate extremes. Atmospheric Sciences Climatology Climate Analysis and Modeling Full Text Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 2 posted You are reading this latest preprint version Show more versions Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7299009","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":496298705,"identity":"d0210043-fae8-4f4e-85b7-c24499710293","order_by":0,"name":"Jitendra Singh","email":"data:image/png;base64,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","orcid":"","institution":"ETH Zurich","correspondingAuthor":true,"prefix":"","firstName":"Jitendra","middleName":"","lastName":"Singh","suffix":""},{"id":496298706,"identity":"829dc0bb-cdd5-45cb-99b2-02c171743704","order_by":1,"name":"Sebastian Sippel","email":"","orcid":"","institution":"Leipzig University, Leipzig, Germany","correspondingAuthor":false,"prefix":"","firstName":"Sebastian","middleName":"","lastName":"Sippel","suffix":""},{"id":496298707,"identity":"65b470f0-025b-4097-8d32-86a7598b21a2","order_by":2,"name":"Lei Gu","email":"","orcid":"","institution":"ETH Zurich","correspondingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Gu","suffix":""},{"id":496298708,"identity":"98527547-0018-41d4-a592-6b0caa4585a4","order_by":3,"name":"Reto Knutti","email":"","orcid":"","institution":"ETH Zurich","correspondingAuthor":false,"prefix":"","firstName":"Reto","middleName":"","lastName":"Knutti","suffix":""},{"id":496298709,"identity":"02694a99-ba37-4220-95b3-e3a577db846d","order_by":4,"name":"Erich Fischer","email":"","orcid":"","institution":"ETH Zurich","correspondingAuthor":false,"prefix":"","firstName":"Erich","middleName":"","lastName":"Fischer","suffix":""}],"badges":[],"createdAt":"2025-08-05 09:43:47","currentVersionCode":2,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-7299009/v2","doiUrl":"https://doi.org/10.21203/rs.3.rs-7299009/v2","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89106917,"identity":"0eb0fcc6-ec7d-4a87-a445-4335646357d8","added_by":"auto","created_at":"2025-08-14 17:52:28","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2450306,"visible":true,"origin":"","legend":"","description":"","filename":"aea0812CombinedPDFv11.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7299009/v2_covered_ea12afdc-a705-4685-a669-7ab4e1b1fe6d.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"Externally forced circulation changes amplify mid-latitude regional heat extremes in climate model nudged-circulation experiments","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7299009/v2","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7299009/v2","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eLarge-scale atmospheric circulation changes have strongly modulated the frequency and intensity of regional heat extremes in the NH mid-latitudes over recent decades. 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