coronal mass ejections - the exhaust of modern dynamos
DESCRIPTION
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
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))
2
Examples ofExamples ofhelical exhaust helical exhaust
3
Sigmoidal structures:Sigmoidal structures:
North/SouthNorth/Southdependence dependence
south
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Sigmoidal filamentsSigmoidal filaments
(from S. Gibson)
5
6
Magnetic helicityMagnetic helicity V
VH d BA
1
2
212 H
11
d d1
SL
H SBA
2 d2
S
SA
1S
1
AB
7
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)
11
Helicity in Magnetic CloudsHelicity in Magnetic Clouds
From fits to a linear force-free field Lynch et al. (2005)
2)()( xBxBM jiij
12
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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14
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
21
Tilt Tilt pol. field regeneration pol. field regeneration
N-shaped (north)S-shaped (south)
standarddynamo picture
internal twistas dynamo feedback
22
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
25
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