coronal mass ejections - the exhaust of modern dynamos
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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 PresentationTRANSCRIPT
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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