Weak, low-level dry convection over Angola determines offshore stratocumulus cloud droplet number concentrations

Weak, low-level dry convection over Angola determines offshore stratocumulus cloud droplet number concentrations | 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 Article Weak, low-level dry convection over Angola determines offshore stratocumulus cloud droplet number concentrations Tyler Tatro, Paquita Zuidema This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9107783/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Boundary-layer cloud interactions involving shortwave-absorbing aerosols remain one of the least understood aerosol influences on climate. Here, we find the highest stratocumulus cloud droplet number concentrations over the southeast Atlantic occur when agricultural fires coincide with synoptically weakened surface warming over Angola, occurring June-early August. Dry convection fills a shallow continental boundary layer with smoke, and a nighttime land breeze transports the aerosol into the marine boundary layer. Offshore aerosol transport is strengthened by low-level easterlies from a continental pressure high southeast of Angola. A stronger continental high ventilates more smoke westward off a cooler Angola. Simultaneously, the south Atlantic subtropical high is weaker, allowing extensive dispersal of aerosol offshore and obscuring marine cloud brightening from shipping. Meteorological co-variation at synoptic scales compensates for any cloud brightening by the smoke, increasing outgoing shortwave radiation by an additional 15%-20% of the monthly mean in June and July. Earth and environmental sciences/Climate sciences/Atmospheric science Earth and environmental sciences/Climate sciences/Atmospheric science/Atmospheric dynamics Full Text Additional Declarations There is NO Competing Interest. Supplementary Files SupplementAngolaLowACITatro.docx Supplement of: Weak, low-level dry convection over Angola determines offshore stratocumulus cloud droplet number concentrations Cite Share Download PDF Status: Under Review Version 1 posted 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-9107783","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":615520291,"identity":"5d26f9d3-23c1-4e7f-b346-07ab0d9a1705","order_by":0,"name":"Tyler Tatro","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA90lEQVRIiWNgGAWjYFAC5gY480BCBUgASQQb4GFgBCkwADIYGB98OAPSwki8FmbDmW0gMQJa7CUSGx9XMPyRt5c+fEyad15tNH87UMuPim24bZFIbDY8w2Bg2MOXlibNu+147ozDjA2MPWdu49PSJtnAYMDYw8NjBtRyLLcBqIWZsQ2vlvafQC32EC1zjuXOJ0JLG9DtBolALcaGMxtqcjcQ1HLmYbNkg4Fxcs8ZtsQHH44dyN0I1HIQn1/Y25MPfmyokLNt72E+cCChpi533vnDBx/8qMCthUEggQEULTBwGEwewK0eCPhRpevwKh4Fo2AUjIKRCQBD0VbfETOLlwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-8439-7249","institution":"Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami","correspondingAuthor":true,"prefix":"","firstName":"Tyler","middleName":"","lastName":"Tatro","suffix":""},{"id":615520292,"identity":"8030107a-148c-4cbc-9726-c6478e685725","order_by":1,"name":"Paquita Zuidema","email":"","orcid":"https://orcid.org/0000-0003-4719-372X","institution":"Rosenstiel School for Marine and Atmospheric Sciences","correspondingAuthor":false,"prefix":"","firstName":"Paquita","middleName":"","lastName":"Zuidema","suffix":""}],"badges":[],"createdAt":"2026-03-12 19:05:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9107783/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9107783/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106403341,"identity":"48785866-33a8-4501-85fa-cd1fe50a9de0","added_by":"auto","created_at":"2026-04-08 09:14:06","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2547326,"visible":true,"origin":"","legend":"","description":"","filename":"atroPZAngolaLowACIMar13submission.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9107783/v1_covered_4ebbe4c0-517f-448b-8c23-163e9cd6f9af.pdf"},{"id":106229868,"identity":"fdda282b-7fde-43ea-9538-7a1b5be511aa","added_by":"auto","created_at":"2026-04-06 12:20:57","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":11304523,"visible":true,"origin":"","legend":"Supplement of: Weak, low-level dry convection over Angola determines offshore stratocumulus cloud droplet number concentrations","description":"","filename":"SupplementAngolaLowACITatro.docx","url":"https://assets-eu.researchsquare.com/files/rs-9107783/v1/9b2821d5ddc1622a7e7b44e5.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Weak, low-level dry convection over Angola determines offshore stratocumulus cloud droplet number concentrations","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9107783/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9107783/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBoundary-layer cloud interactions involving shortwave-absorbing aerosols remain one of the least understood aerosol influences on climate. Here, we find the highest stratocumulus cloud droplet number concentrations over the southeast Atlantic occur when agricultural fires coincide with synoptically weakened surface warming over Angola, occurring June-early August. Dry convection fills a shallow continental boundary layer with smoke, and a nighttime land breeze transports the aerosol into the marine boundary layer. Offshore aerosol transport is strengthened by low-level easterlies from a continental pressure high southeast of Angola. A stronger continental high ventilates more smoke westward off a cooler Angola. Simultaneously, the south Atlantic subtropical high is weaker, allowing extensive dispersal of aerosol offshore and obscuring marine cloud brightening from shipping. 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