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Detection of Negative Effective Magnetic Pressure Instability in Turbulence Simulations
Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).ORCID-id: 0000-0002-7304-021X
Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
Vise andre og tillknytning
2011 (engelsk)Inngår i: Astrophysical Journal, ISSN 0004-637X, EISSN 1538-4357, Vol. 740, nr 2, s. L50-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We present the first numerical demonstration of the negative effective magnetic pressure instability in direct numerical simulations of stably stratified, externally forced, isothermal hydromagnetic turbulence in the regime of large plasma beta. By the action of this instability, initially uniform horizontal magnetic field forms flux concentrations whose scale is large compared to the turbulent scale. We further show that the magnetic energy of these large-scale structures is only weakly dependent on the magnetic Reynolds number. Our results support earlier mean-field calculations and analytic work that identified this instability. Applications to the formation of active regions in the Sun are discussed.

sted, utgiver, år, opplag, sider
2011. Vol. 740, nr 2, s. L50-
Emneord [en]
magnetohydrodynamics: MHD, Sun: dynamo, sunspots, turbulence
HSV kategori
Identifikatorer
URN: urn:nbn:se:su:diva-70035DOI: 10.1088/2041-8205/740/2/L50ISI: 000296752600019OAI: oai:DiVA.org:su-70035DiVA, id: diva2:478731
Merknad

authorCount :6;

Tilgjengelig fra: 2012-01-16 Laget: 2012-01-16 Sist oppdatert: 2019-12-12bibliografisk kontrollert
Inngår i avhandling
1. From mean-field hydromagnetics to solar magnetic flux concentrations
Åpne denne publikasjonen i ny fane eller vindu >>From mean-field hydromagnetics to solar magnetic flux concentrations
2012 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

The main idea behind the work presented in this thesis is to investigate if it is possible to find a mechanism that leads to surface magnetic field concentrations and could operate under solar conditions without postulating the presence of magnetic flux tubes rising from the bottom of the convection zone, a commonly used yet physically problematic approach.

In this context we study the ‘negative effective magnetic pressure effect’: it was pointed out in earlier work (Kleeorin et al., 1989) that the presence of a weak magnetic field can lead to a reduction of the mean turbulent pressure on large length scales. This reduction is now indeed clearly observed in simulations.

As magnetic fluctuations experience an unstable feedback through this effect, it leads, in a stratified medium, to the formation of magnetic structures, first observed numerically in the fifth paper of this thesis. While our setup is relatively simple, one wonders if this instability, as a mechanism able to concentrate magnetic fields in the near surface layers, may play a role in the formation of sunspots, starting from a weak dynamo-generated field throughout the convection zone rather than from strong flux tubes stored at the bottom.

A generalization of the studied case is ongoing.

sted, utgiver, år, opplag, sider
Stockholm: Department of Astronomy, Stockholm University, 2012. s. 51
Emneord
magneto-hydrodynamics, solar physics, turbulence
HSV kategori
Forskningsprogram
astronomi
Identifikatorer
urn:nbn:se:su:diva-80817 (URN)978-91-7447-576-0 (ISBN)
Disputas
2012-10-26, sal FB42 , AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:30 (engelsk)
Opponent
Veileder
Merknad

At the time of the the doctoral defence the following paper was unpublished and had a status as follows: Paper nr 7: Submitted

Tilgjengelig fra: 2012-10-04 Laget: 2012-09-28 Sist oppdatert: 2012-10-01bibliografisk kontrollert

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