{"@context":{"@vocab":"https://cir.nii.ac.jp/schema/1.0/","rdfs":"http://www.w3.org/2000/01/rdf-schema#","dc":"http://purl.org/dc/elements/1.1/","dcterms":"http://purl.org/dc/terms/","foaf":"http://xmlns.com/foaf/0.1/","prism":"http://prismstandard.org/namespaces/basic/2.0/","cinii":"http://ci.nii.ac.jp/ns/1.0/","datacite":"https://schema.datacite.org/meta/kernel-4/","ndl":"http://ndl.go.jp/dcndl/terms/","jpcoar":"https://github.com/JPCOAR/schema/blob/master/2.0/"},"@id":"https://cir.nii.ac.jp/crid/1360011146586796928.json","@type":"Article","productIdentifier":[{"identifier":{"@type":"DOI","@value":"10.1029/1999ja900439"}},{"identifier":{"@type":"URI","@value":"https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1029%2F1999JA900439"}},{"identifier":{"@type":"URI","@value":"https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JA900439"}}],"dc:title":[{"@value":"Mountains versus valleys: Semiannual variation of geomagnetic activity"}],"description":[{"type":"abstract","notation":[{"@value":"<jats:p>The semiannual variation in geomagnetic activity is generally attributed to the Russell‐McPherron effect. In that picture, enhancements of southward field <jats:italic>B<jats:sub>s</jats:sub></jats:italic>, near the equinoxes account for the observed higher geomagnetic activity in March and September. In a contrary point of view, we argue that the bulk of the semiannual variation results from an equinoctial effect (based on the Ψ angle between the solar wind flow direction and Earth's dipole axis) that makes <jats:italic>B<jats:sub>s</jats:sub></jats:italic>, coupling less effective (by ∼25% on average) at the solstices. Thus the semiannual variation is not simply due to “mountain building” (creation of <jats:italic>B<jats:sub>s</jats:sub></jats:italic>) at the equinoxes but results primarily from “valley digging” (loss of coupling efficiency) at the solstices. We estimate that this latter effect, which clearly reveals itself in the diurnal variation of the <jats:italic>am</jats:italic> index, is responsible for ∼65% of the semiannual modulation. The characteristic imprint of the equinoctial hypothesis is also apparent in hourly/monthly averages of the time‐differentiated <jats:italic>Dst</jats:italic> index and the <jats:italic>AE</jats:italic> index.</jats:p>"}]}],"creator":[{"@id":"https://cir.nii.ac.jp/crid/1380011146586796930","@type":"Researcher","foaf:name":[{"@value":"E. W. Cliver"}]},{"@id":"https://cir.nii.ac.jp/crid/1380011146586796929","@type":"Researcher","foaf:name":[{"@value":"Y. Kamide"}]},{"@id":"https://cir.nii.ac.jp/crid/1380011146586796928","@type":"Researcher","foaf:name":[{"@value":"A. G. Ling"}]}],"publication":{"publicationIdentifier":[{"@type":"PISSN","@value":"01480227"}],"prism:publicationName":[{"@value":"Journal of Geophysical Research: Space Physics"}],"dc:publisher":[{"@value":"American Geophysical Union (AGU)"}],"prism:publicationDate":"2000-02","prism:volume":"105","prism:number":"A2","prism:startingPage":"2413","prism:endingPage":"2424"},"reviewed":"false","dc:rights":["http://onlinelibrary.wiley.com/termsAndConditions#vor"],"url":[{"@id":"https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1029%2F1999JA900439"},{"@id":"https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JA900439"}],"createdAt":"2002-09-17","modifiedAt":"2023-09-23","relatedProduct":[{"@id":"https://cir.nii.ac.jp/crid/1360004229800776576","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Annual variations in westward auroral electrojet and substorm occurrence rate during solar cycle 23"}]},{"@id":"https://cir.nii.ac.jp/crid/1360298345008304256","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Extreme solar events"}]},{"@id":"https://cir.nii.ac.jp/crid/1360302865541545216","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"The Extreme Space Weather Event of 1872 February: Sunspots, Magnetic Disturbance, and Auroral Displays"}]},{"@id":"https://cir.nii.ac.jp/crid/1360306905635893120","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Comparative Observations of the Outer Belt Electron Fluxes and Precipitated Relativistic Electrons"}]},{"@id":"https://cir.nii.ac.jp/crid/1360567179755572480","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"MLT and seasonal dependence of auroral electrojets: IMAGE magnetometer network observations"}]},{"@id":"https://cir.nii.ac.jp/crid/1360567180786640640","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Geomagnetic Indices"}]},{"@id":"https://cir.nii.ac.jp/crid/1360580230594858368","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Probabilistic modelling of substorm occurrences with an echo state network"}]},{"@id":"https://cir.nii.ac.jp/crid/1360857593667332608","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Echo state network model for analyzing solar-wind effects on the AU and AL indices"}]},{"@id":"https://cir.nii.ac.jp/crid/1361131644403587840","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Intense Geomagnetic Storm during Maunder Minimum Possibly by a Quiescent Filament Eruption"}]},{"@id":"https://cir.nii.ac.jp/crid/1390001206512503040","@type":"Article","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@language":"en","@value":"Understanding the “SEKKI” phenomena in Japanese historical literatures based on the modern science of low-latitude aurora"}]},{"@id":"https://cir.nii.ac.jp/crid/2050870366939654528","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Automatic selection of Dst storms and their seasonal variations in two versions of Dst in 50 years"}]}],"dataSourceIdentifier":[{"@type":"CROSSREF","@value":"10.1029/1999ja900439"},{"@type":"CROSSREF","@value":"10.1002/2013ja019742_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"},{"@type":"CROSSREF","@value":"10.1186/bf03353323_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"},{"@type":"CROSSREF","@value":"10.1007/s41116-022-00033-8_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"},{"@type":"CROSSREF","@value":"10.3847/1538-4357/acc6cc_references_DOI_RmM4vjNyYYPBYvtr9uF5L7DTapD"},{"@type":"CROSSREF","@value":"10.1029/2024gl109673_references_DOI_RmM4vjNyYYPBYvtr9uF5L7DTapD"},{"@type":"CROSSREF","@value":"10.1002/2014ja019843_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"},{"@type":"CROSSREF","@value":"10.1007/978-90-481-9858-0_8_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"},{"@type":"CROSSREF","@value":"10.1186/s40623-017-0642-2_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"},{"@type":"CROSSREF","@value":"10.5194/angeo-40-11-2022_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"},{"@type":"CROSSREF","@value":"10.5194/angeo-41-529-2023_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"},{"@type":"CROSSREF","@value":"10.3847/1538-4357/ab107e_references_DOI_WK0KrdvUsMTIpfixw4bW99YD4XD"}]}