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Magnetic bipoles in rotating turbulence with coronal envelope
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.ORCID iD: 0000-0002-7304-021X
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, article id A61Article in journal (Refereed) Published
Abstract [en]

Context. The formation mechanism of sunspots and starspots is not yet fully understood. It is a major open problem in astrophysics. Aims. Magnetic flux concentrations can be produced by the negative effective magnetic pressure instability (NEMPI). This instability is strongly suppressed by rotation. However, the presence of an outer coronal envelope was previously found to strengthen the flux concentrations and make them more prominent. It also allows for the formation of bipolar regions (BRs). We aim to understand the important issue of whether the presence of an outer coronal envelope also changes the excitation conditions and the rotational dependence of NEMPI. Methods. We have used direct numerical simulations and mean-field simulations. We adopted a simple two-layer model of turbulence that mimics the jump between the convective turbulent and coronal layers below and above the surface of a star, respectively. The computational domain is Cartesian and located at a certain latitude of a rotating sphere. We investigated the effects of rotation on NEMPI by changing the Coriolis number, the latitude, the strengths of the imposed magnetic field, and the box resolution. Results. Rotation has a strong impact on the process of BR formation. Even rather slow rotation is found to suppress BR formation. However, increasing the imposed magnetic field strength also makes the structures stronger and alleviates the rotational suppression somewhat. The presence of a coronal layer itself does not significantly reduce the effects of rotational suppression.

Place, publisher, year, edition, pages
EDP SCIENCES S A , 2019. Vol. 621, article id A61
Keywords [en]
magnetohydrodynamics (MHD), turbulence, dynamo, Sun: magnetic fields, Sun: rotation, Sun: activity
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-241309DOI: 10.1051/0004-6361/201833018ISI: 000455172300001Scopus ID: 2-s2.0-85059893132OAI: oai:DiVA.org:kth-241309DiVA, id: diva2:1282731
Note

QC 20190125

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-25Bibliographically approved

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Losada, IllaWarnecke, JörnBrandenburg, AxelKleeorin, NathanRogachevskii, l.

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