Revisiting The Rare Transition of a South Atlantic Cyclone to Tropical Storm Akará: Energy Cycle and Stratosphere-Troposphere Interaction

Revisiting The Rare Transition of a South Atlantic Cyclone to Tropical Storm Akará: Energy Cycle and Stratosphere-Troposphere Interaction | 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 Revisiting The Rare Transition of a South Atlantic Cyclone to Tropical Storm Akará: Energy Cycle and Stratosphere-Troposphere Interaction Danilo Couto de Souza, Victor Antunes Ranieri, Pedro Leite da Silva Dias, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6536558/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Feb, 2026 Read the published version in Climate Dynamics → Version 1 posted 5 You are reading this latest preprint version Abstract Cyclone Akará was the third documented tropical cyclone in the South Atlantic, undergoing a rare subtropical-to-tropical transition in February 2024. This study investigates the dynamical, thermodynamical, and energetic evolution of Akará using a diagnostic framework combining the Lorenz Energy Cycle (LEC) and heat and vorticity budgets. Akará originated in a post-frontal, weakly baroclinic environment characterized by warm sea surface temperatures (>28$\circ C$), strong ocean-atmosphere thermal contrast, and low vertical wind shear. These conditions favored convective activity and led to the development of a symmetric warm core, initially supported by latent heat release and interaction with an upper-level cutoff low. As the system intensified, it transitioned into a tropical cyclone, exhibiting a deep warm core and organized convection. Stratospheric air intrusions were identified during and after the tropical transition, contributing to upper-tropospheric warming and enhancing cyclone intensification. Heat and vorticity budget analyses revealed how vertical motion, latent heat release, and vortex stretching shaped the storm’s three-dimensional structure and contributed to its deepening. During the mature stage, Akará reached peak intensity while moving over cooler waters. Although convective activity decreased, the warm core was sustained—likely through continued stratosphere-troposphere interactions and strong barotropic energy conversions at low and mid levels. The combined use of LEC and budget diagnostics proved effective in disentangling the physical mechanisms behind Akará's evolution, offering valuable insight into the dynamics of rare South Atlantic tropical transitions. Expanding such analyses to other events is essential to improve our understanding and forecasting of tropical cyclogenesis in this basin. Tropical Transition South Atlantic Cyclones Lorenz Energy Cycle Stratosphere-Troposphere Interaction Heat and Vorticity Budgets Barotropic Conversions Latent Heat Release Full Text Cite Share Download PDF Status: Published Journal Publication published 09 Feb, 2026 Read the published version in Climate Dynamics → Version 1 posted Editorial decision: Major Revision 28 Jul, 2025 Reviewers agreed at journal 05 Jun, 2025 Reviewers invited by journal 04 Jun, 2025 Editor assigned by journal 23 May, 2025 First submitted to journal 13 May, 2025 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-6536558","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":466674481,"identity":"41cda67c-95ac-486d-9d03-7dc6a122186a","order_by":0,"name":"Danilo Couto de 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This study investigates the dynamical, thermodynamical, and energetic evolution of Akará using a diagnostic framework combining the Lorenz Energy Cycle (LEC) and heat and vorticity budgets. Akará originated in a post-frontal, weakly baroclinic environment characterized by warm sea surface temperatures (\u0026gt;28$\\circ C$), strong ocean-atmosphere thermal contrast, and low vertical wind shear. These conditions favored convective activity and led to the development of a symmetric warm core, initially supported by latent heat release and interaction with an upper-level cutoff low. As the system intensified, it transitioned into a tropical cyclone, exhibiting a deep warm core and organized convection. Stratospheric air intrusions were identified during and after the tropical transition, contributing to upper-tropospheric warming and enhancing cyclone intensification. Heat and vorticity budget analyses revealed how vertical motion, latent heat release, and vortex stretching shaped the storm’s three-dimensional structure and contributed to its deepening. During the mature stage, Akará reached peak intensity while moving over cooler waters. Although convective activity decreased, the warm core was sustained—likely through continued stratosphere-troposphere interactions and strong barotropic energy conversions at low and mid levels. The combined use of LEC and budget diagnostics proved effective in disentangling the physical mechanisms behind Akará's evolution, offering valuable insight into the dynamics of rare South Atlantic tropical transitions. 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