Large-scale to local factors influencing Sumatra squalls affecting Singapore

Large-scale to local factors influencing Sumatra squalls affecting Singapore | 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 Large-scale to local factors influencing Sumatra squalls affecting Singapore Hanh Nguyen, Muhammad E Hassim, Jia Yan Huan, Xin Rong Chua, Chen Chen, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5607311/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Jul, 2025 Read the published version in Climate Dynamics → Version 1 posted 5 You are reading this latest preprint version Abstract The weather and climate of the Maritime Continent, including Singapore, is influenced by a wide range of tropical drivers including the El-Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), the Madden-Julian Oscillation (MJO), and equatorial wave activity. In Singapore, the rainfall pattern is often characterised by episodes of short intense rainfall bursts, which are dominated by mesoscale convective systems, such as Sumatra squall lines, and often lead to local flash floods and strong wind bursts. Here we analyse 33 years of Sumatra squalls affecting Singapore and investigate the potential impact of the main modes of climate variability and atmospheric equatorial tropical waves. Highlighted results are that, on average, Sumatra squalls originate from Sumatra and the Strait of Malacca, make landfall over Singapore in the morning and last about 2 hours, and are more frequent from April to November. These squalls tend to be more frequent under La Niña conditions which are associated with locally warm sea surface temperature anomalies and favourable atmospheric anomalies over the Maritime continent region. Additionally, it is shown that the MJO may play a role in setting the westerlies favorable for the squalls to propagate eastward, convectively-coupled Kelvin waves are important for the initiation of the squalls over Sumatra and the Strait of Malacca, while equatorial Rossby, and mixed Rossby gravity waves influence the direction of propagation of the squalls from Sumatra and/or the Strait of Malacca toward Singapore. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Full Text Supplementary Files FigureA1toA3.docx Cite Share Download PDF Status: Published Journal Publication published 23 Jul, 2025 Read the published version in Climate Dynamics → Version 1 posted Reviewers agreed at journal 24 Mar, 2025 Reviewers invited by journal 23 Mar, 2025 Editor assigned by journal 03 Mar, 2025 First submitted to journal 27 Feb, 2025 Editorial decision: Minor Revision 30 Jan, 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-5607311","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":432813396,"identity":"6c7dcd68-bf59-4796-9502-d57c00c0e260","order_by":0,"name":"Hanh Nguyen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7ElEQVRIiWNgGAWjYBACAwYGNhib8THJWpiNSdbCJk2UFnP2s8ceMO6oTdxwvPdYdUHFNgZ59x4Dhp9tuLVY9uSlGzCeOZ644cy5tNszztxmMDxzxoCxF48WgwM5ZhKMbccSN9zIMbvN2wbUMiMtgYEXn5bzb6Ba7r8xK4ZpYfyLT8sNsC01QFt4zJhBWuQlkg8w47XlBtCWxLYDxjPP5BhLA/3CY8Bz+MBhmXP4HAa05WNbnWzf8TOGnwsqbsvJtzc2PnxThlsLGCQwHGZQOABh8xgAGQcIaACBOgb5BigTzhgFo2AUjIJRAAUAyVJWUxPXS/gAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-1287-1324","institution":"Australian Bureau of Meteorology","correspondingAuthor":true,"prefix":"","firstName":"Hanh","middleName":"","lastName":"Nguyen","suffix":""},{"id":432813397,"identity":"17f10b02-c3f1-4f1a-951d-b3e60794c4ba","order_by":1,"name":"Muhammad E Hassim","email":"","orcid":"","institution":"Centre for Climate research Singapore","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"E","lastName":"Hassim","suffix":""},{"id":432813398,"identity":"61effdba-4eae-448e-8d81-2a4e6484fc71","order_by":2,"name":"Jia Yan Huan","email":"","orcid":"","institution":"Meteorological service Singapore","correspondingAuthor":false,"prefix":"","firstName":"Jia","middleName":"Yan","lastName":"Huan","suffix":""},{"id":432813399,"identity":"8a170f74-2f89-4dd0-8524-c6baf407bcef","order_by":3,"name":"Xin Rong Chua","email":"","orcid":"","institution":"CCRS","correspondingAuthor":false,"prefix":"","firstName":"Xin","middleName":"Rong","lastName":"Chua","suffix":""},{"id":432813400,"identity":"0f3e2a9c-d9b4-4f58-9e33-0429b308b12e","order_by":4,"name":"Chen Chen","email":"","orcid":"","institution":"CCRS","correspondingAuthor":false,"prefix":"","firstName":"Chen","middleName":"","lastName":"Chen","suffix":""},{"id":432813401,"identity":"4825432b-735c-41d0-a656-dac27b36d15f","order_by":5,"name":"Matthew C Wheeler","email":"","orcid":"","institution":"Australian Bureau of Meteorology","correspondingAuthor":false,"prefix":"","firstName":"Matthew","middleName":"C","lastName":"Wheeler","suffix":""},{"id":432813402,"identity":"a7f3c98f-8f4f-4da8-b244-50e1e60460c6","order_by":6,"name":"Bradley F Murphy","email":"","orcid":"","institution":"Australian Bureau of Meteorology","correspondingAuthor":false,"prefix":"","firstName":"Bradley","middleName":"F","lastName":"Murphy","suffix":""},{"id":432813403,"identity":"22cd1eaa-b5e5-46e4-8aa0-c678fa33a985","order_by":7,"name":"Sandeep Sahany","email":"","orcid":"","institution":"CCRS","correspondingAuthor":false,"prefix":"","firstName":"Sandeep","middleName":"","lastName":"Sahany","suffix":""},{"id":432813404,"identity":"3e44ff89-70b0-4616-bc69-7eb5a4678e3b","order_by":8,"name":"Aurel F Moise","email":"","orcid":"","institution":"CCRS","correspondingAuthor":false,"prefix":"","firstName":"Aurel","middleName":"F","lastName":"Moise","suffix":""},{"id":432813405,"identity":"7213feda-5d0e-4385-a6ab-e7cfeef87bd8","order_by":9,"name":"Simon C Peatman","email":"","orcid":"","institution":"CCRS","correspondingAuthor":false,"prefix":"","firstName":"Simon","middleName":"C","lastName":"Peatman","suffix":""}],"badges":[],"createdAt":"2024-12-09 08:49:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5607311/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5607311/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00382-025-07766-w","type":"published","date":"2025-07-23T15:58:13+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":79733717,"identity":"b3cd6952-0eee-44f6-8063-09c0216e600f","added_by":"auto","created_at":"2025-04-02 06:34:18","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":80368,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of the Sumatra squalls (SS) identified from 33 years of radar images. Monthly (a), diurnal (b), duration over Singapore (SG) (c), and yearly (d) occurrences of the squalls with missing years in grey shading. The monthly distribution shows squalls that did (aqua) and did not (grey) make landfall over Singapore, and their duration. In panels b-f, only the ones that made landfall are accounted for the statistics. Timeseries of the annual mean Ocean Niño Index (ONI; dotted line with circle markers) and Dipole Mode Index (DMI; solid line with star markers) are included with El Niño/positive IOD years in red solid circles/stars (ONI≥0.5/DMI\u0026gt;0.4) and La Niña/negative IOD years in blue solid circles/stars (ONI≤-0.5/DMI\u0026lt;-0.4). Note that the annual DMI is averaged over Jul-Oct when the IOD is most active while the ONI is averaged over July of each year to June the following year. Weighted (annual mean) distribution of Sumatra squalls by phases of (e) ENSO and (f) IOD.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/9145b0638eaf3d55a8df5c97.jpg"},{"id":79733718,"identity":"7a449bae-3491-4226-b394-ac636a267996","added_by":"auto","created_at":"2025-04-02 06:34:18","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":59299,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Monthly distribution of the Sumatra squalls as a function of their place of origin: Sumatra (Sum), the Strait of Malacca (SOM), both Sum and SOM (Sum/SOM), and other if they are from neither Sum nor SOM. (b) Monthly distribution of the Sumatra squalls as a function of their direction of propagation: eastward (E), southeastward (SE), northeastward (NE) or other if they have another direction than E, SE or NE. The detected squalls that did not make landfall over Singapore are shown in grey. The distribution is based on data over the period 2013-2023.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/3616d43d2538fca182c2c7db.jpg"},{"id":79733720,"identity":"78e0c5a1-b938-45ee-9c1f-97e122efd11d","added_by":"auto","created_at":"2025-04-02 06:34:18","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":122903,"visible":true,"origin":"","legend":"\u003cp\u003eTime-lag composite of ERA5 vertically integrated (surface-300 hPa) mass weighted moisture flux convergence (MFC, shading, units are [m/s][g/kg]), 850 hPa winds (vectors, units are m/s) and GPM IMERG V7 rainfall (contours, from 0.75mm/hr every 0.5mm/hr, in increasing order from purple to yellow) averaged over the Sumatra squall occurrences that made landfall over Singapore.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/897157fe60489f965056cfb5.jpg"},{"id":79734542,"identity":"3ed68ab5-22dd-482f-8055-e6d604672c72","added_by":"auto","created_at":"2025-04-02 06:42:18","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":53742,"visible":true,"origin":"","legend":"\u003cp\u003eFiltered ERA5 OLR and 850 hPa wind anomalies in the MJO, Kelvin wave, ER wave and MRG wave bands averaged over the Sumatra squall occurrences that made landfall over Singapore . Anomalies associated with MRG wave are multiplied by a factor of 3.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/57129130b154eaaa9160f46c.jpg"},{"id":79733724,"identity":"3c2453cb-9bf9-48dd-b2d8-69bbc95882e8","added_by":"auto","created_at":"2025-04-02 06:34:18","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":35715,"visible":true,"origin":"","legend":"\u003cp\u003eDifference between the equatorial wave composites averaged over the Sumatra squall occurrences that made landfall and impacted Singapore (Fig. 4) and of those that did not make landfall at time lag of +2 hours (Fig. A2).\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/56d621960095cf97f5b56e8f.jpg"},{"id":79734543,"identity":"5643e448-2c4c-4ba6-8c9c-95cec5bf7819","added_by":"auto","created_at":"2025-04-02 06:42:18","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":281620,"visible":true,"origin":"","legend":"\u003cp\u003eSame as Fig. 4 but averaged over the Sumatra squall occurrences \u0026nbsp;that moved a) northeastward (163 occurrences), b) eastward (147 occurrences) and c) southeastward (64 occurrence) over the period of 2013-2023, and made landfall over Singapore.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/1f73fd37dfe16d50218ae78b.jpg"},{"id":79733728,"identity":"f3698019-70e8-4acb-8d6f-1dd88e0088ab","added_by":"auto","created_at":"2025-04-02 06:34:18","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":47480,"visible":true,"origin":"","legend":"\u003cp\u003eTime-lag composite of ERA5 vertical moisture advection at gridpoint nearest Singapore (1.25°N-103.75°E) averaged over Sumatra squalls that moved a) northeastward (163 occurrences), b) eastward (147 occurrences) and c) southeastward (64 occurrence) over the period of 2013-2023, and made landfall over Singapore.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/7703d96b1a50472813394275.jpg"},{"id":79733722,"identity":"b07c37df-491f-4e8d-9f94-dd3e8af64531","added_by":"auto","created_at":"2025-04-02 06:34:18","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":41314,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram summarising the impact of different drivers on the Sumatra squalls affecting Singapore. The squall is represented by the grey feature initiating over Sumatra, and the arrow indicating its propagation. The shadings mimic enhanced convection/precipitation and the arrows indicate the low level wind anomalies impacting the direction of propagation of the squall. Increased precipitation associated with La Niña condition is in light blue, the MJO impact on both enhanced convection and westerlies is in green, the westerlies and enhanced convection of the KW is in cyan blue, the cyclonic cells associated with the ER wave is in red, and the cross-equatorial winds (could be northerly or southerly depending on the direction of circulation) associated with the MRG wave gyre is in purple. Note that while all forcings are sketched in one panel, they do not necessary occur simultaneously for a Sumatra squall to develop and propagate. The exact location of each wave can also differ.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/55800ef50651d545a54b0cad.jpg"},{"id":87756912,"identity":"d13f0006-7861-4fe0-9e9a-93208d4b4170","added_by":"auto","created_at":"2025-07-28 16:10:19","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1160574,"visible":true,"origin":"","legend":"","description":"","filename":"ClimDynRev1clean.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1_covered_4fb1e4e1-0527-41d3-83c4-18a18b39f972.pdf"},{"id":79733721,"identity":"b7d963c3-46ed-4931-9244-7d0b63912e58","added_by":"auto","created_at":"2025-04-02 06:34:18","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1088803,"visible":true,"origin":"","legend":"","description":"","filename":"FigureA1toA3.docx","url":"https://assets-eu.researchsquare.com/files/rs-5607311/v1/cf6157c139d6aa1b9f1d9293.docx"}],"financialInterests":"","formattedTitle":"Large-scale to local factors influencing Sumatra squalls affecting Singapore","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"climate-dynamics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cldy","sideBox":"Learn more about [Climate Dynamics](https://www.springer.com/journal/382)","snPcode":"382","submissionUrl":"https://submission.nature.com/new-submission/382/3","title":"Climate Dynamics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5607311/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5607311/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"The weather and climate of the Maritime Continent, including Singapore, is influenced by a wide range of tropical drivers including the El-Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), the Madden-Julian Oscillation (MJO), and equatorial wave activity. In Singapore, the rainfall pattern is often characterised by episodes of short intense rainfall bursts, which are dominated by mesoscale convective systems, such as Sumatra squall lines, and often lead to local flash floods and strong wind bursts. Here we analyse 33 years of Sumatra squalls affecting Singapore and investigate the potential impact of the main modes of climate variability and atmospheric equatorial tropical waves. Highlighted results are that, on average, Sumatra squalls originate from Sumatra and the Strait of Malacca, make landfall over Singapore in the morning and last about 2 hours, and are more frequent from April to November. These squalls tend to be more frequent under La Niña conditions which are associated with locally warm sea surface temperature anomalies and favourable atmospheric anomalies over the Maritime continent region. Additionally, it is shown that the MJO may play a role in setting the westerlies favorable for the squalls to propagate eastward, convectively-coupled Kelvin waves are important for the initiation of the squalls over Sumatra and the Strait of Malacca, while equatorial Rossby, and mixed Rossby gravity waves influence the direction of propagation of the squalls from Sumatra and/or the Strait of Malacca toward Singapore.","manuscriptTitle":"Large-scale to local factors influencing Sumatra squalls affecting Singapore","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-02 06:34:13","doi":"10.21203/rs.3.rs-5607311/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-03-25T02:19:45+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-23T23:01:17+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-03T05:21:38+00:00","index":"","fulltext":""},{"type":"submitted","content":"Climate Dynamics","date":"2025-02-27T23:46:36+00:00","index":"","fulltext":""},{"type":"decision","content":"Minor Revision","date":"2025-01-30T09:13:58+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"climate-dynamics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cldy","sideBox":"Learn more about [Climate Dynamics](https://www.springer.com/journal/382)","snPcode":"382","submissionUrl":"https://submission.nature.com/new-submission/382/3","title":"Climate Dynamics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ccb98e17-1c93-46fd-9fc9-3f942e3a53be","owner":[],"postedDate":"April 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-28T16:06:53+00:00","versionOfRecord":{"articleIdentity":"rs-5607311","link":"https://doi.org/10.1007/s00382-025-07766-w","journal":{"identity":"climate-dynamics","isVorOnly":false,"title":"Climate Dynamics"},"publishedOn":"2025-07-23 15:58:13","publishedOnDateReadable":"July 23rd, 2025"},"versionCreatedAt":"2025-04-02 06:34:13","video":"","vorDoi":"10.1007/s00382-025-07766-w","vorDoiUrl":"https://doi.org/10.1007/s00382-025-07766-w","workflowStages":[]},"version":"v1","identity":"rs-5607311","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5607311","identity":"rs-5607311","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}