Coronal Mass Ejections - the exhaust of modern dynamos

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Coronal Mass Ejections Coronal Mass Ejections - the exhaust of modern - the exhaust of modern dynamos dynamos Examples: systematic swirl Examples: systematic swirl (helicity) (helicity) Measuring it quantitatively Measuring it quantitatively Connection with the dynamo Connection with the dynamo Axel Brandenburg ( Axel Brandenburg ( Nordita, Stockholm Nordita, Stockholm ) )

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Coronal Mass Ejections - the exhaust of modern dynamos. Examples: systematic swirl (helicity) Measuring it quantitatively Connection with the dynamo Axel Brandenburg ( Nordita, Stockholm ). Examples of helical exhaust. Sigmoidal structures: North/South dependence. south. - PowerPoint PPT Presentation

Transcript of Coronal Mass Ejections - the exhaust of modern dynamos

Page 1: Coronal Mass Ejections - the exhaust of modern dynamos

Coronal Mass Ejections - the Coronal Mass Ejections - the exhaust of modern dynamosexhaust of modern dynamos

Examples: systematic swirl (helicity)Examples: systematic swirl (helicity)

Measuring it quantitativelyMeasuring it quantitatively

Connection with the dynamoConnection with the dynamo

Axel Brandenburg (Axel Brandenburg (Nordita, StockholmNordita, Stockholm))

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Examples ofExamples ofhelical exhaust helical exhaust

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Sigmoidal structures:Sigmoidal structures:

North/SouthNorth/Southdependence dependence

south

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Sigmoidal filamentsSigmoidal filaments

(from S. Gibson)

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Magnetic helicityMagnetic helicity V

VH d BA

1

2

212 H

11

d d1

SL

H SBA

2 d2

S

SA

1S

1

AB

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Flux crossingsFlux crossings V

VH d BA

1

2

212 H

J. Chae (2000, ApJ)

+

+

++ - -

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It’s a popular logo too…It’s a popular logo too…

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Magnetic helicity from crossingsMagnetic helicity from crossingsJ. Chae (2000, ApJ)

++ - -

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Current helicity and Current helicity and magn. hel. Fluxmagn. hel. Flux

Bao & Zhang (1998),neg. in north, plus in south

(also Seehafer 1990)

Berger & Ruzmaikin (2000)

cycle/Mx104 246S

NDeVore (2000)

cycle/Mx10 246

(for BR & CME)

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Helicity in Magnetic CloudsHelicity in Magnetic Clouds

From fits to a linear force-free field Lynch et al. (2005)

2)()( xBxBM jiij

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Helicity from time seriesHelicity from time series

)()( xBxBM jiij

)(

)()(

kHki

kEkkkM

kijk

jiijij

)()( xBxBM jiij

)()()( rxxr jiij BBM

Matthaeus et al. (1982)

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Nindos et al. (2003)

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Nindos &Andrews (2004)

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Magnetic helicity conservationMagnetic helicity conservation

2221

d

dJBJuB

t

0d

d 2/12/121 BJBBuBA

t

kkBJ 2/1How J diverges as 0

Ideal limit and ideal case similar!

2/112/1221

d

d uωωfuωt

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No helicity production by flowsbut segragation in space:

H<0

H>0

Generates toroidalfrom poloidal field

Poloidal field regenerated bytilting (Coriolis force)

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Twisting an existing tube:Twisting an existing tube:segragation in spectral spacesegragation in spectral space

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Cancelling magn helicityCancelling magn helicityintroduced in single tubeintroduced in single tube

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-effect dynamos (large scale)-effect dynamos (large scale)

Differential rotation(prehelioseism: faster inside)

Cyclonic convection;Buoyant flux tubes Equatorward

migration

New loop

-effect?need meridional circulation

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Tilt Tilt pol. field regeneration pol. field regeneration

N-shaped (north)S-shaped (south)

standarddynamo picture

internal twistas dynamo feedback

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Production of LS helicityProduction of LS helicity

0 baBABA

bjforcing produces uω baand

bBB jJJ aAA

Yousef & BrandenburgA&A 407, 7 (2003)

But no net helicity production

baBA therefore:

alpha effect

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Problems with Problems with -effect -effect • Catastrophic quenching??

– ~ Rm-1, t ~ Rm

-1

– Field strength vanishingly small!?!

• Something wrong with simulations– so let’s ignore the problem

• Possible reasons:– Suppression of lagrangian chaos?– Suffocation from small scale magnetic helicity?

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Connection with Connection with effect: effect: writhe with writhe with internalinternal twist as by-product twist as by-product

clockwise tilt(right handed)

left handedinternal twist

031 / bjuω both for thermal/magnetic

buoyancy

JBB

T dt

d2

T

BBJ

effect produces

helical field

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Simulations: forced turbulence w/shearSimulations: forced turbulence w/shear

Negative current helicity:net production in northern hemisphere

SJE d2 Sje d21046 Mx2/cycle

Brandenburg & Sandin (2004, A&A 427, 13)

Helicity fluxes from shear: Vishniac & Cho (2001, ApJ 550, 752)Subramanian & Brandenburg (2004, PRL 93, 20500)

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Saturation: 50% energy in large scalesSaturation: 50% energy in large scales

geometryhere relevantto the sun

no helicity, e.g.

azimuthallyaveraged

neg helicity(northern hem.)

...21

JWBB

a

t

Rogachevskii & Kleeorin (2003, 2004)

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ConclusionConclusion • 11 yr cycle• Dyamo (SS vs LS)• Problems

– -quenching– slow saturation

• Solution– Modern -effect theory– j.b contribution– Magnetic helicity fluxes

• Location of dynamo– Distrubtion, shaped by– near-surface shear

1046 Mx2/cycle