A Statistical Study of Seasonal and Interhemispheric Asymmetries in Low-Latitude Pi2 Pulsations Across All Local Times

A Statistical Study of Seasonal and Interhemispheric Asymmetries in Low-Latitude Pi2 Pulsations Across All Local Times | 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 A Statistical Study of Seasonal and Interhemispheric Asymmetries in Low-Latitude Pi2 Pulsations Across All Local Times Akihiko Ueda, Shun Imajo This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7182174/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Dec, 2025 Read the published version in Earth, Planets and Space → Version 1 posted 5 You are reading this latest preprint version Abstract This study statistically investigates the seasonal and interhemispheric asymmetry of low-latitude Pi2 pulsations by analyzing 6026 events from 2013--2017 geomagnetic data at the conjugate stations Kakioka (KAK) and Alice Springs (ASP). The east-west (D) component amplitude is significantly enhanced near the solar terminator, with a strong dawn-dusk asymmetry; the enhancement is most pronounced at dawn (around 06:00--09:00 LT) during local summer, whereas at dusk it extends into the nightside. In contrast, while the nightside north-south (H) component amplitude lacks clear seasonality, the dayside H component is systematically larger in the summer hemisphere across both morning and afternoon sectors. This is opposite to the D component in the afternoon, which tends to be smaller in summer. On the nightside, the D-component amplitude is persistently larger in the summer hemisphere. Dayside features in both the D and H components are largely explained by a model combining the ionospheric current system with remote effects of nightside field-aligned currents (FACs). We suggest that the non-seasonality of the nightside H component is due to its dominance by compressional waves, as the low-conductivity nightside ionosphere is effectively transparent to this wave mode. These compressional waves are coupled with Alfvén waves that drive oscillating FACs, which in turn results in the observed seasonal variation of the D component and dayside H component. Pi2 pulsation Ionospheric current Ionospheric conductivity Seasonal variation Hemispheric asymmetry Terminator effect Full Text Supplementary Files monthLTDtoHampmaxmedian1.png Cite Share Download PDF Status: Published Journal Publication published 05 Dec, 2025 Read the published version in Earth, Planets and Space → Version 1 posted Reviewers agreed at journal 05 Aug, 2025 Reviewers invited by journal 05 Aug, 2025 Editor assigned by journal 05 Aug, 2025 First submitted to journal 04 Aug, 2025 Editorial decision: Major Revision 28 Jul, 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-7182174","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":496269746,"identity":"f7c32618-ba30-4d95-b749-51cce492e6a0","order_by":0,"name":"Akihiko Ueda","email":"data:image/png;base64,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","orcid":"","institution":"Nagoya University: Nagoya Daigaku","correspondingAuthor":true,"prefix":"","firstName":"Akihiko","middleName":"","lastName":"Ueda","suffix":""},{"id":496269747,"identity":"bcdd8d43-dee1-4624-946a-6127f5511964","order_by":1,"name":"Shun Imajo","email":"","orcid":"","institution":"Kyoto University: Kyoto Daigaku","correspondingAuthor":false,"prefix":"","firstName":"Shun","middleName":"","lastName":"Imajo","suffix":""}],"badges":[],"createdAt":"2025-07-22 03:47:56","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7182174/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7182174/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40623-025-02327-1","type":"published","date":"2025-12-05T15:57:16+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":97723790,"identity":"f0cddb8a-b24c-4294-ba40-7313b098955e","added_by":"auto","created_at":"2025-12-08 16:06:24","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1316432,"visible":true,"origin":"","legend":"","description":"","filename":"mainv3.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7182174/v1_covered_1db08f8b-fe1e-4144-aea1-7a68d824b937.pdf"},{"id":88758253,"identity":"877428b2-61ad-4a33-9419-a7c98416a6e0","added_by":"auto","created_at":"2025-08-11 07:34:14","extension":"png","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":134271,"visible":true,"origin":"","legend":"","description":"","filename":"monthLTDtoHampmaxmedian1.png","url":"https://assets-eu.researchsquare.com/files/rs-7182174/v1/304af224ff05a3ae1044c971.png"}],"financialInterests":"","formattedTitle":"A Statistical Study of Seasonal and Interhemispheric Asymmetries in Low-Latitude Pi2 Pulsations Across All Local Times","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":"earth-planets-and-space","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"epsp","sideBox":"Learn more about [Earth, Planets and Space](http://earth-planets-space.springeropen.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/epsp/default.aspx","title":"Earth, Planets and Space","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Pi2 pulsation, Ionospheric current, Ionospheric conductivity, Seasonal variation, Hemispheric asymmetry, Terminator effect","lastPublishedDoi":"10.21203/rs.3.rs-7182174/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7182174/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"This study statistically investigates the seasonal and interhemispheric asymmetry of low-latitude Pi2 pulsations by analyzing 6026 events from 2013--2017 geomagnetic data at the conjugate stations Kakioka (KAK) and Alice Springs (ASP). The east-west (D) component amplitude is significantly enhanced near the solar terminator, with a strong dawn-dusk asymmetry; the enhancement is most pronounced at dawn (around 06:00--09:00 LT) during local summer, whereas at dusk it extends into the nightside. In contrast, while the nightside north-south (H) component amplitude lacks clear seasonality, the dayside H component is systematically larger in the summer hemisphere across both morning and afternoon sectors. This is opposite to the D component in the afternoon, which tends to be smaller in summer. On the nightside, the D-component amplitude is persistently larger in the summer hemisphere. Dayside features in both the D and H components are largely explained by a model combining the ionospheric current system with remote effects of nightside field-aligned currents (FACs). We suggest that the non-seasonality of the nightside H component is due to its dominance by compressional waves, as the low-conductivity nightside ionosphere is effectively transparent to this wave mode. These compressional waves are coupled with Alfvén waves that drive oscillating FACs, which in turn results in the observed seasonal variation of the D component and dayside H component.","manuscriptTitle":"A Statistical Study of Seasonal and Interhemispheric Asymmetries in Low-Latitude Pi2 Pulsations Across All Local Times","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-11 07:34:09","doi":"10.21203/rs.3.rs-7182174/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-08-06T01:21:18+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-06T01:05:50+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-05T10:45:06+00:00","index":"","fulltext":""},{"type":"submitted","content":"Earth, Planets and Space","date":"2025-08-05T02:54:10+00:00","index":"","fulltext":""},{"type":"decision","content":"Major Revision","date":"2025-07-28T21:24:26+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"earth-planets-and-space","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"epsp","sideBox":"Learn more about [Earth, Planets and Space](http://earth-planets-space.springeropen.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/epsp/default.aspx","title":"Earth, Planets and Space","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"06a1c281-8a7d-43ec-aee5-6d9d8d0c8f2e","owner":[],"postedDate":"August 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-08T16:00:00+00:00","versionOfRecord":{"articleIdentity":"rs-7182174","link":"https://doi.org/10.1186/s40623-025-02327-1","journal":{"identity":"earth-planets-and-space","isVorOnly":false,"title":"Earth, Planets and Space"},"publishedOn":"2025-12-05 15:57:16","publishedOnDateReadable":"December 5th, 2025"},"versionCreatedAt":"2025-08-11 07:34:09","video":"","vorDoi":"10.1186/s40623-025-02327-1","vorDoiUrl":"https://doi.org/10.1186/s40623-025-02327-1","workflowStages":[]},"version":"v1","identity":"rs-7182174","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7182174","identity":"rs-7182174","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}