Urban Boundary-Layer Dynamics During Extreme Heat in Paris

Urban Boundary-Layer Dynamics During Extreme Heat in Paris | 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 Urban Boundary-Layer Dynamics During Extreme Heat in Paris Jani Strömberg, Sasu Karttunen, Simone Kotthaus, Marc-Antoine Drouin, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8732780/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Urban boundary-layer (UBL) processes are important to understand the complex interactions between the surface and atmosphere. Increased surface rough-ness and heat storage are typically attributed to the larger fraction of builtsurfaces in urban areas. Heatwaves lead to stronger heat storage and to extremeconvective UBLs, which is one of many applications where large-eddy simu-lations (LES) offe an accurate modelling methodology of complex turbulentcharacteristics in urban flw studies. This study investigates the structure, tur-bulence characteristics and measurement implications of UBL in Paris, France,during a heatwave in July 2022. High-resolution LES simulations (4–16 m) produced with PALM model system are evaluated against observations from the PANAME 2022 campaign,including eddy-covariance fluxe (EC), Doppler wind lidar (DWL) profilesand near-surface measurements from the M´et´eo-France observation network.In addition, wavelet analysis is used to examine resolved turbulent scales and vertical coupling at typical urban measurement heights. PALM reproduces the temporal variability of sensible heat fluxe at the SIRTA observatory with an 67.9 W m−2 and a bias of 34.5 W m−2, while momentum-related quantities show larger deviations, particularly during weaknighttime stratification Near-surface temperatures are well captured across the M´et´eo-France network, with an RMSE of 1.18 ◦C and mean bias of -0.63 ◦C. DWL comparisons show that PALM captures the growth and decay of the UBL at urban and suburban sites, with maximum UBL heights reach-ing 2.4 km in the city centre, approximately 10% higher than in more ruralconditions. Neighbourhood-scale turbulent motions (O(100 m)) dominate ver-tical transport during daytime convective conditions, with contributions fromlarger scales depending on measurement height and location. These resultsdemonstrate the capability of high-resolution LES to represent convective UBL dynamics during extreme heat and to assess the representativeness of urbanatmospheric measurements. Overall, this study provides one of the firs city toneighbourhood-scale LES analyses of an extreme convective UBL supportedby multiple observations. By linking resolved turbulent scales to vertical cou-pling and measurement height, the results infer when and where urban ECobservations remain representative under strongly unstable conditions. Thefinding offe practical guidance for the interpretation and design of urbanmeasurements and highlight the importance of resolving neighbourhood-scaleturbulence in urban flw modelling applications. Atmospheric surface layer Convective boundary-layer Large49 eddy simulation Turbulence Urban boundary-layer Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 10 Mar, 2026 Reviews received at journal 09 Mar, 2026 Reviews received at journal 25 Feb, 2026 Reviews received at journal 17 Feb, 2026 Reviewers agreed at journal 31 Jan, 2026 Reviewers agreed at journal 30 Jan, 2026 Reviewers agreed at journal 30 Jan, 2026 Reviewers invited by journal 30 Jan, 2026 Editor assigned by journal 29 Jan, 2026 Submission checks completed at journal 29 Jan, 2026 First submitted to journal 29 Jan, 2026 You are reading this latest preprint version 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. We do this by developing innovative software and high quality services for the global research community. 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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-8732780","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":583650318,"identity":"754f8e94-d732-42d1-800f-ff1954ee6e5e","order_by":0,"name":"Jani 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Increased surface rough-ness and heat storage are typically attributed to the larger fraction of builtsurfaces in urban areas. Heatwaves lead to stronger heat storage and to extremeconvective UBLs, which is one of many applications where large-eddy simu-lations (LES) offe an accurate modelling methodology of complex turbulentcharacteristics in urban flw studies. This study investigates the structure, tur-bulence characteristics and measurement implications of UBL in Paris, France,during a heatwave in July 2022.\u003c/p\u003e\n\u003cp\u003eHigh-resolution LES simulations (4–16 m) produced with PALM model system are evaluated against observations from the PANAME 2022 campaign,including eddy-covariance fluxe (EC), Doppler wind lidar (DWL) profilesand near-surface measurements from the M´et´eo-France observation network.In addition, wavelet analysis is used to examine resolved turbulent scales and vertical coupling at typical urban measurement heights.\u003c/p\u003e\n\u003cp\u003ePALM reproduces the temporal variability of sensible heat fluxe at the SIRTA observatory with an 67.9 W m−2 and a bias of 34.5 W m−2, while momentum-related quantities show larger deviations, particularly during weaknighttime stratification Near-surface temperatures are well captured across the M´et´eo-France network, with an RMSE of 1.18 ◦C and mean bias of -0.63 ◦C. 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