{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T10:31:52Z","timestamp":1753871512069,"version":"3.41.2"},"reference-count":47,"publisher":"American Geophysical Union (AGU)","issue":"10","license":[{"start":{"date-parts":[[2021,9,28]],"date-time":"2021-09-28T00:00:00Z","timestamp":1632787200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":["agupubs.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["JGR Space Physics"],"published-print":{"date-parts":[[2021,10]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>The separation of contributions from different sources in the magnetic field signal measured at satellite altitude is an open challenge. An approach to this problem, using Principal Component Analysis, is here applied to geomagnetic external field series at Virtual Observatories (VOs). These series are computed from an enlarged data set of Swarm data covering all local times and all geomagnetic activity levels between January 2014 and December 2019. For each 30\u2010day time window, the Equivalent Source Dipole technique is used to reduce all measurements inside a cylinder to one single \u201cobservation\u201d at its axis and 500\u00a0km altitude. Our results reveal a first principal mode with dipolar geometry and time variation following very closely the RC\u2010index of geomagnetic activity. They display a resolved second principal mode with annual periodicity and of approximately zonal quadrupolar radial pattern, reminiscent of results in a previous study using VO series from a filtered satellite data set and with lower time resolution. We resort to the recent comprehensive model CM6 to identify a possible source for this second mode. We propose that the dipolar mode is the expression of the magnetospheric ring current dynamics, at 30\u2010day time resolution, and the quadrupolar mode is the expression of the annual asymmetry between local summer and winter Sq current vortices. Two fainter modes could be related to the equinoctial amplification of Sq vortices and the ionospheric dynamo modulation by nonmigrating tides. We show that a more uniform local time sampling could contribute to better resolve ionospheric structures.<\/jats:p>","DOI":"10.1029\/2021ja029579","type":"journal-article","created":{"date-parts":[[2021,9,12]],"date-time":"2021-09-12T18:46:58Z","timestamp":1631472418000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["The Signature of Geomagnetic Field External Drivers in Virtual Observatory 30\u2010day Means Derived From Swarm Data"],"prefix":"10.1029","volume":"126","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5032-0190","authenticated-orcid":false,"given":"D.","family":"Saturnino","sequence":"first","affiliation":[{"name":"Laboratoire de Plan\u00e9tologie et G\u00e9odynamique UMR\u20106112, CNRS Universit\u00e9 de Nantes Universit\u00e9 d\u2019Angers  Nantes France"},{"name":"University of Coimbra CITEUC, Geophysical and Astronomical Observatory  Coimbra Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2729-2897","authenticated-orcid":false,"given":"M. A.","family":"Pais","sequence":"additional","affiliation":[{"name":"University of Coimbra CITEUC, Geophysical and Astronomical Observatory  Coimbra Portugal"},{"name":"Department of Physics University of Coimbra  Coimbra Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8396-4520","authenticated-orcid":false,"given":"J.","family":"Domingos","sequence":"additional","affiliation":[{"name":"University of Coimbra CITEUC, Geophysical and Astronomical Observatory  Coimbra Portugal"},{"name":"Department of Physics University of Coimbra  Coimbra Portugal"}]}],"member":"13","published-online":{"date-parts":[[2021,9,28]]},"reference":[{"key":"e_1_2_11_2_1","doi-asserted-by":"publisher","DOI":"10.1093\/gji\/ggy297"},{"key":"e_1_2_11_3_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-246x.2009.04111.x"},{"key":"e_1_2_11_4_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.asr.2017.02.037"},{"volume-title":"Satellites: Orbits and missions","year":"2005","author":"Capderou M.","key":"e_1_2_11_5_1"},{"key":"e_1_2_11_6_1","doi-asserted-by":"publisher","DOI":"10.1186\/s40623-016-0481-6"},{"key":"e_1_2_11_7_1","doi-asserted-by":"publisher","DOI":"10.1186\/s40623-018-0983-5"},{"key":"e_1_2_11_8_1","doi-asserted-by":"publisher","DOI":"10.1186\/s40623-016-0486-1"},{"key":"e_1_2_11_9_1","doi-asserted-by":"publisher","DOI":"10.1186\/s40623-015-0274-3"},{"key":"e_1_2_11_10_1","doi-asserted-by":"publisher","DOI":"10.1186\/bf03351933"},{"key":"e_1_2_11_11_1","doi-asserted-by":"publisher","DOI":"10.1029\/2012JA017683"},{"key":"e_1_2_11_12_1","doi-asserted-by":"publisher","DOI":"10.5047\/eps.2013.09.003"},{"volume-title":"Local estimation of the earth\u2019s core magnetic field","year":"2018","author":"Hammer M. D.","key":"e_1_2_11_13_1"},{"key":"e_1_2_11_14_1","doi-asserted-by":"publisher","DOI":"10.1186\/s40623-021-01357-9"},{"key":"e_1_2_11_15_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.jastp.2004.01.034"},{"volume-title":"Principal component analysis","year":"2002","author":"Jolliffe I. T.","key":"e_1_2_11_16_1"},{"key":"e_1_2_11_17_1","doi-asserted-by":"publisher","DOI":"10.1029\/2003je002048"},{"key":"e_1_2_11_18_1","doi-asserted-by":"publisher","DOI":"10.1007\/s11214-016-0275-y"},{"key":"e_1_2_11_19_1","doi-asserted-by":"publisher","DOI":"10.1051\/swsc\/2020023"},{"key":"e_1_2_11_20_1","doi-asserted-by":"publisher","DOI":"10.1029\/2008JA013064"},{"key":"e_1_2_11_21_1","doi-asserted-by":"publisher","DOI":"10.1007\/s11214-016-0267-y"},{"key":"e_1_2_11_22_1","doi-asserted-by":"publisher","DOI":"10.1029\/2020GC008976"},{"key":"e_1_2_11_23_1","doi-asserted-by":"publisher","DOI":"10.5047\/eps.2013.07.011"},{"key":"e_1_2_11_24_1","doi-asserted-by":"publisher","DOI":"10.1029\/2006gl026616"},{"key":"e_1_2_11_25_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-246X.2005.02691.x"},{"key":"e_1_2_11_26_1","first-page":"119","article-title":"Inversion of satellite magnetic anomaly data","volume":"45","author":"Mayhew M. A.","year":"1979","journal-title":"Geophysical Journal"},{"key":"e_1_2_11_27_1","doi-asserted-by":"publisher","DOI":"10.1007\/s10291-019-0931-2"},{"key":"e_1_2_11_28_1","doi-asserted-by":"publisher","DOI":"10.1029\/2011JA016779"},{"key":"e_1_2_11_29_1","doi-asserted-by":"publisher","DOI":"10.1029\/2006JA012015"},{"key":"e_1_2_11_30_1","doi-asserted-by":"publisher","DOI":"10.1175\/1520-0493(1982)110<0699:SEITEO>2.0.CO;2"},{"key":"e_1_2_11_31_1","doi-asserted-by":"publisher","DOI":"10.1029\/2007GL032397"},{"key":"e_1_2_11_32_1","doi-asserted-by":"publisher","DOI":"10.1186\/s40645-014-0031-4"},{"key":"e_1_2_11_33_1","doi-asserted-by":"publisher","DOI":"10.1002\/2014JE004734"},{"key":"e_1_2_11_34_1","doi-asserted-by":"publisher","DOI":"10.1093\/gji\/ggu033"},{"key":"e_1_2_11_35_1","doi-asserted-by":"publisher","DOI":"10.1029\/2019JA027694"},{"key":"e_1_2_11_36_1","doi-asserted-by":"publisher","DOI":"10.1029\/2010JA016289"},{"key":"e_1_2_11_37_1","doi-asserted-by":"publisher","DOI":"10.1007\/978-3-642-97123-5"},{"key":"e_1_2_11_38_1","doi-asserted-by":"publisher","DOI":"10.1029\/96GL00388"},{"key":"e_1_2_11_39_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-246x.2004.02421.x"},{"key":"e_1_2_11_40_1","doi-asserted-by":"publisher","DOI":"10.1186\/s40623-020-01210-5"},{"key":"e_1_2_11_41_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.pepi.2017.06.004"},{"volume-title":"An improved description of earth\u2019s external magnetic fields and their source regions using satellite data","year":"2013","author":"Shore R. M.","key":"e_1_2_11_42_1"},{"key":"e_1_2_11_43_1","doi-asserted-by":"publisher","DOI":"10.1002\/2015ja022066"},{"volume-title":"Swarm level 1b product definition, SW\u2010RS\u2010DSC\u2010SY\u20100007","year":"2018","author":"Toffner\u2010Clausen L.","key":"e_1_2_11_44_1"},{"key":"e_1_2_11_45_1","doi-asserted-by":"publisher","DOI":"10.1002\/2013EO450001"},{"key":"e_1_2_11_46_1","doi-asserted-by":"publisher","DOI":"10.1007\/s11214-016-0282-z"},{"key":"e_1_2_11_47_1","doi-asserted-by":"publisher","DOI":"10.1029\/2011JA016487"},{"key":"e_1_2_11_48_1","doi-asserted-by":"publisher","DOI":"10.1029\/2009JA014638"}],"container-title":["Journal of Geophysical Research: Space Physics"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/onlinelibrary.wiley.com\/doi\/pdf\/10.1029\/2021JA029579","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/onlinelibrary.wiley.com\/doi\/full-xml\/10.1029\/2021JA029579","content-type":"application\/xml","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/agupubs.onlinelibrary.wiley.com\/doi\/pdf\/10.1029\/2021JA029579","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,8,25]],"date-time":"2023-08-25T14:27:29Z","timestamp":1692973649000},"score":1,"resource":{"primary":{"URL":"https:\/\/agupubs.onlinelibrary.wiley.com\/doi\/10.1029\/2021JA029579"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,9,28]]},"references-count":47,"journal-issue":{"issue":"10","published-print":{"date-parts":[[2021,10]]}},"alternative-id":["10.1029\/2021JA029579"],"URL":"https:\/\/doi.org\/10.1029\/2021ja029579","archive":["Portico"],"relation":{},"ISSN":["2169-9380","2169-9402"],"issn-type":[{"type":"print","value":"2169-9380"},{"type":"electronic","value":"2169-9402"}],"subject":[],"published":{"date-parts":[[2021,9,28]]},"assertion":[{"value":"2021-06-02","order":0,"name":"received","label":"Received","group":{"name":"publication_history","label":"Publication History"}},{"value":"2021-09-03","order":1,"name":"accepted","label":"Accepted","group":{"name":"publication_history","label":"Publication History"}},{"value":"2021-09-28","order":2,"name":"published","label":"Published","group":{"name":"publication_history","label":"Publication History"}}],"article-number":"e2021JA029579"}}