Self-organized magnetic structures Self-organized magnetic structures in computational astrophysicsin computational astrophysics

Axel Brandenburg (Nordita/Stockholm)

Kemel+12Kemel+12 Ilonidis+11Ilonidis+11 Brandenburg+13Brandenburg+13Warnecke+11Warnecke+11KKäpylääpylä+12+12

Today

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B-class flares?

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Oct2003

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Flights rerouted

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Rerouted

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6 March

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7 March

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8 March

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Magnetic fields from the SunMagnetic fields from the Suna) Motions from

i. Convection instabilityii. Magnetorotational inst.iii. Supernova forcing

b) Dynamo instabilityi. Stretch-twist-foldii. Turbulent dynamo

White light

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Tips of icebergs:Magnetic flux concentrations in magnetogram!

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ParkerParker’’s (1955) dynamo waves (1955) dynamo wave

Differential rotation(faster inside) Cyclonic convection;

Buoyant flux tubesEquatorward

migration

New loop

-effect

Doppler imaging: distant stars

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II Peg: rapidly rotating binary

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RS CVn type Canum Venaticorum

Kochukhov, M

antere, et al (2013)S

aar & B

randenburg (1999)

Brun, Brown, Browning, Miesch, ToomreBrun, Brown, Browning, Miesch, Toomre

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• Cycle now common!

• Activity from bottom of CZ

• but at high latitudes

Ghizaru, Ghizaru, Charbonneau, Charbonneau,

Racine, …Racine, …

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Dynamo wave from simulations Kap

yla et al (2012)

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Dynamo is one example of self-organizationDynamo is one example of self-organization

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Alternative sunspot originsAlternative sunspot origins

Theories for shallow spots:Theories for shallow spots:

(i) Collapse by suppression(i) Collapse by suppressionof turbulent heat fluxof turbulent heat flux

(ii) Negative pressure effects(ii) Negative pressure effectsfrom <from <uuiiuujj> vs > vs BBiiBBjj

Kosovichev et al. (2000)

Kosovichev et al. (2000)

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Negative effective magnetic pressure instability

• Gas+turb. press equil.

• B increases

• Turb. press. Decreases

• Net effect?

Self-assembly of a magnetic spot• Minimalistic model• 2 ingredients:

– Stratification & turbulence

• Extensions– Coupled to dynamo– Compete with rotation– Radiation/ionization

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Mean-field models: different

scale separation

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Varying turbulent diffusivity

Bi-polar regions, found by accident

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Warnecke et al. (2013, subm

itted)

PencilPencilcodecode

• Started in Sept. 2001 with Wolfgang Dobler• High order (6th order in space, 3rd order in time)• Cache & memory efficient• MPI, can run PacxMPI (across countries!)• Maintained/developed by ~80 people (SVN)• Automatic validation (over night or any time)• 0.0013 s/pt/step at 10243 , 2048 procs• http://pencil-code.googlecode.com

• Isotropic turbulence– MHD, passive scl, CR

• Stratified layers– Convection, radiation

• Shearing box– MRI, dust, interstellar– Self-gravity

• Sphere embedded in box– Fully convective stars– geodynamo

• Other applications– Chemistry, combustion– Spherical coordinates

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Increase of revision number Increase of revision number

User meetings:User meetings:2005 Copenhagen2006 Copenhagen2007 Stockholm2008 Leiden2009 Heidelberg2010 New York2011 Toulouse2012 Helsinki2013 Lund2014 Gottingen

Pencil h-index

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Red line givesthe diagonal to see the crossing

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Automatic validation testsAutomatic validation tests

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Increase in # of auto testsIncrease in # of auto tests

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Online data reduction and visualizationOnline data reduction and visualization

non-helically forced turbulence

Conclusions• Turbulence can possess surprising effects

– Large scale dynamos– Magnetic flux concentrations

• Importance for space weather

• Run-time data evaluation, etc

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