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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).
Visa övriga samt affilieringar
2011 (Engelska)Ingår i: Astrophysical Journal, ISSN 0004-637X, EISSN 1538-4357, Vol. 740, nr 2, s. L50-Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
2011. Vol. 740, nr 2, s. L50-
Nyckelord [en]
magnetohydrodynamics: MHD, Sun: dynamo, sunspots, turbulence
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Identifikatorer
URN: urn:nbn:se:su:diva-70035DOI: 10.1088/2041-8205/740/2/L50ISI: 000296752600019OAI: oai:DiVA.org:su-70035DiVA, id: diva2:478731
Anmärkning

authorCount :6;

Tillgänglig från: 2012-01-16 Skapad: 2012-01-16 Senast uppdaterad: 2019-12-12Bibliografiskt granskad
Ingår i avhandling
1. From mean-field hydromagnetics to solar magnetic flux concentrations
Öppna denna publikation i ny flik eller fönster >>From mean-field hydromagnetics to solar magnetic flux concentrations
2012 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Astronomy, Stockholm University, 2012. s. 51
Nyckelord
magneto-hydrodynamics, solar physics, turbulence
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Forskningsämne
astronomi
Identifikatorer
urn:nbn:se:su:diva-80817 (URN)978-91-7447-576-0 (ISBN)
Disputation
2012-10-26, sal FB42 , AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:30 (Engelska)
Opponent
Handledare
Anmärkning

At the time of the the doctoral defence the following paper was unpublished and had a status as follows: Paper nr 7: Submitted

Tillgänglig från: 2012-10-04 Skapad: 2012-09-28 Senast uppdaterad: 2012-10-01Bibliografiskt granskad

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Av författaren/redaktören
Brandenburg, AxelKemel, Koen
Av organisationen
Nordiska institutet för teoretisk fysik (Nordita)
Astronomi, astrofysik och kosmologi

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