Transition from axi- to nonaxisymmetric dynamo modes in spherical convection models of solar-like stars

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en
dc.contributor.author Viviani, Mariangela
dc.contributor.author Warnecke, Jörn
dc.contributor.author Käpylä, Maarit J.
dc.contributor.author Käpylä, Petri J.
dc.contributor.author Olspert, Nigul
dc.contributor.author Cole-Kodikara, Elizabeth M.
dc.contributor.author Lehtinen, Jyri J.
dc.contributor.author Brandenburg, Axel
dc.date.accessioned 2018-10-16T08:56:02Z
dc.date.available 2018-10-16T08:56:02Z
dc.date.issued 2018-08-01
dc.identifier.citation Viviani , M , Warnecke , J , Käpylä , M J , Käpylä , P J , Olspert , N , Cole-Kodikara , E M , Lehtinen , J J & Brandenburg , A 2018 , ' Transition from axi- to nonaxisymmetric dynamo modes in spherical convection models of solar-like stars ' ASTRONOMY AND ASTROPHYSICS , vol 616 , A160 , pp. 1-19 . DOI: 10.1051/0004-6361/201732191 en
dc.identifier.issn 0004-6361
dc.identifier.issn 1432-0746
dc.identifier.other PURE UUID: a731b346-b269-4045-90f1-e289e32df509
dc.identifier.other PURE ITEMURL: https://research.aalto.fi/en/publications/transition-from-axi-to-nonaxisymmetric-dynamo-modes-in-spherical-convection-models-of-solarlike-stars(a731b346-b269-4045-90f1-e289e32df509).html
dc.identifier.other PURE LINK: http://adsabs.harvard.edu/abs/2017arXiv171010222V
dc.identifier.other PURE FILEURL: https://research.aalto.fi/files/28518978/aa32191_17.pdf
dc.identifier.uri https://aaltodoc.aalto.fi/handle/123456789/34308
dc.description.abstract Context. Both dynamo theory and observations of stellar large-scale magnetic fields suggest a change from nearly axisymmetric configurations at solar rotation rates to nonaxisymmetric configurations for rapid rotation. Aims. We seek to understand this transition using numerical simulations. Methods. We use three-dimensional simulations of turbulent magnetohydrodynamic convection in spherical shell wedges and considered rotation rates between 1 and 31 times the solar value. Results. We find a transition from axi- to nonaxisymmetric solutions at around 1.8 times the solar rotation rate. This transition coincides with a change in the rotation profile from antisolar- to solar-like differential rotation with a faster equator and slow poles. In the solar-like rotation regime, the field configuration consists of an axisymmetric oscillatory field accompanied by an m = 1 azimuthal mode (two active longitudes), which also shows temporal variability. At slow (rapid) rotation, the axisymmetric (nonaxisymmetric) mode dominates. The axisymmetric mode produces latitudinal dynamo waves with polarity reversals, while the nonaxisymmetric mode often exhibits a slow drift in the rotating reference frame and the strength of the active longitudes changes cyclically over time between the different hemispheres. In the majority of cases we find retrograde waves, while prograde waves are more often found from observations. Most of the obtained dynamo solutions exhibit cyclic variability either caused by latitudinal or azimuthal dynamo waves. In an activity-period diagram, the cycle lengths normalized by the rotation period form two different populations as a function of rotation rate or magnetic activity level. The slowly rotating axisymmetric population lies close to what in observations is called the inactive branch, where the stars are believed to have solar-like differential rotation, while the rapidly rotating models are close to the superactive branch with a declining cycle to rotation frequency ratio and an increasing rotation rate. Conclusions. We can successfully reproduce the transition from axi- to nonaxisymmetric dynamo solutions for high rotation rates, but high-resolution simulations are required to limit the effect of rotational quenching of convection at rotation rates above 20 times the solar value. en
dc.format.extent 1-19
dc.format.mimetype application/pdf
dc.language.iso en en
dc.relation.ispartofseries ASTRONOMY AND ASTROPHYSICS en
dc.relation.ispartofseries Volume 616 en
dc.rights openAccess en
dc.subject.other 113 Computer and information sciences en
dc.title Transition from axi- to nonaxisymmetric dynamo modes in spherical convection models of solar-like stars en
dc.type A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä fi
dc.description.version Peer reviewed en
dc.contributor.department Max Planck Institute for Solar System Research
dc.contributor.department Department of Computer Science
dc.contributor.department University of Helsinki
dc.contributor.department NORDITA
dc.subject.keyword Astrophysics - Solar and Stellar Astrophysics
dc.subject.keyword Magnetohydrodynamics – convection – turbulence – Sun
dc.subject.keyword dynamo
dc.subject.keyword rotation
dc.subject.keyword activity
dc.subject.keyword 113 Computer and information sciences
dc.identifier.urn URN:NBN:fi:aalto-201810165385
dc.identifier.doi 10.1051/0004-6361/201732191
dc.type.version publishedVersion


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