Solar Cycle Occurrence of Alfvénic Fluctuations and Related Geo-Efficiency

dc.contributorAalto-yliopistofi
dc.contributorAalto Universityen
dc.contributor.authorTanskanen, Eija
dc.contributor.authorSnekvik, K.
dc.contributor.authorSlavin, J. A.
dc.contributor.authorPérez-Suárez, D.
dc.contributor.authorViljanen, A.
dc.contributor.authorGoldstein, M. L.
dc.contributor.authorKäpylä, M.J.
dc.contributor.authorHynönen, Reko
dc.contributor.authorHäkkinen, L. V. T.
dc.contributor.authorMursula, K.
dc.contributor.departmentDepartment of Electronics and Nanoengineering
dc.contributor.departmentUniversity of Bergen
dc.contributor.departmentUniversity of Michigan, Ann Arbor
dc.contributor.departmentUniversity College London
dc.contributor.departmentFinnish Meteorological Institute
dc.contributor.departmentSpace Science Institute
dc.contributor.departmentDepartment of Computer Science
dc.contributor.departmentUniversity of Oulu
dc.date.accessioned2017-11-21T13:37:37Z
dc.date.available2017-11-21T13:37:37Z
dc.date.issued2017
dc.description.abstractWe examine solar wind intervals with Alfvénic fluctuations (ALFs) in 1995–2011. The annual number, the total annual duration, and the average length of ALFs vary over the solar cycle, having a maximum in 2003 and a minimum in 2009. ALFs are most frequent in the declining phase of solar cycle, when the number of high-speed streams at the Earth's vicinity is increased. There is a rapid transition after the maximum of solar cycle 23 from ALFs being mainly embedded in slow solar wind (<400 km/s) until 2002 to ALFs being dominantly in fast solar wind (>600 km/s) since 2003. Cross helicity increased by 30% from 2002 to 2003 and maximized typically 4–6 h before solar wind speed maximum. Cross helicity remained elevated for several days for highly Alfvénic non-ICME streams, but only for a few hours for ICMEs. The number of substorms increased by about 40% from 2002 to 2003, and the annual number of substorms closely follows the annual cross helicity. This further emphasizes the role of Alfvénic fluctuations in modulating substorm activity. The predictability of substorm frequency and size would be greatly improved by monitoring solar wind Alfvénic fluctuations in addition to the mean values of the important solar wind parameters.en
dc.description.versionPeer revieweden
dc.format.extent10
dc.format.mimetypeapplication/pdf
dc.identifier.citationTanskanen , E , Snekvik , K , Slavin , J A , Pérez-Suárez , D , Viljanen , A , Goldstein , M L , Käpylä , M J , Hynönen , R , Häkkinen , L V T & Mursula , K 2017 , ' Solar Cycle Occurrence of Alfvénic Fluctuations and Related Geo-Efficiency ' , Journal of geophysical research: Space physics , vol. 122 , no. 10 , pp. 9848-9857 . https://doi.org/10.1002/2017JA024385en
dc.identifier.doi10.1002/2017JA024385
dc.identifier.issn2169-9380
dc.identifier.issn2169-9402
dc.identifier.otherPURE UUID: 9235407a-a070-457e-a239-d3a78301bf14
dc.identifier.otherPURE ITEMURL: https://research.aalto.fi/en/publications/9235407a-a070-457e-a239-d3a78301bf14
dc.identifier.otherPURE FILEURL: https://research.aalto.fi/files/15854333/Tanskanen_et_al_2017_Journal_of_Geophysical_Research_Space_Physics.pdf
dc.identifier.urihttps://aaltodoc.aalto.fi/handle/123456789/28828
dc.identifier.urnURN:NBN:fi:aalto-201711217649
dc.language.isoenen
dc.relation.ispartofseriesJOURNAL OF GEOPHYSICAL RESEARCH: SPACE PHYSICSen
dc.rightsopenAccessen
dc.subject.keywordSolar wind plasma
dc.subject.keywordPlasma waves and turbulence
dc.subject.keywordSolar cycle variations
dc.subject.keywordSubstorms
dc.subject.keywordMagnetic fields and magnetism
dc.subject.keywordAlfvénic fluctuations
dc.subject.keywordSpace climate
dc.subject.keywordGeomagnetic activity
dc.subject.keywordSolar cycle time scales
dc.subject.keywordHigh-speed streams
dc.titleSolar Cycle Occurrence of Alfvénic Fluctuations and Related Geo-Efficiencyen
dc.typeA1 Alkuperäisartikkeli tieteellisessä aikakauslehdessäfi
dc.type.versionpublishedVersion
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