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Apologies from Ed and Karl-HeinzApologies from Ed and Karl-Heinz

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SoFin@NOTSoFin@NOT

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Near-surface shear layer:Near-surface shear layer:spots rooted at spots rooted at r/Rr/R=0.95?=0.95?

Benevolenskaya, Hoeksema, Kosovichev, Scherrer (1999) Pulkkinen & Tuominen (1998)

nHz 473/360024360

/7.14

ds

do

o

=AZ=(180/) (1.5x107) (210-8)

=360 x 0.15 = 54 degrees!

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Forced large scale dynamo with fluxesForced large scale dynamo with fluxes

geometryhere relevantto the sun

Negative current helicity:net production in northern hemisphere

SJE d2 Sje d2

1046 Mx2/cycle

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Solar dynamos in the 1970sSolar dynamos in the 1970s

• Distributed dynamo (Roberts & Stix 1972)

– Positive alpha, negative shear

Yoshimura (1975)

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Distributed dynamosDistributed dynamos• max at 60 Mm depth

• t = 3x1012 cm2/s

depth [cgs] Urms Beq [d] t[cgs]

24 0.004 70 1600 1.3 1.5

39 0.01 56 2000 2.8 2

150 0.12 25 3000 22 3

200 0.2 4 600 160 0.6

Krivodubskii (1984)

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In the days before In the days before helioseismologyhelioseismology

• Angular velocity (at 4o latitude): – very young spots: 473 nHz

– oldest spots: 462 nHz

– Surface plasma: 452 nHz

• Conclusion back then:– Sun spins faster in deaper convection zone

– Solar dynamo works with d/dr<0: equatorward migr

Before helioseismologyBefore helioseismology• Angular velocity (at 4o latitude):

– very young spots: 473 nHz– oldest spots: 462 nHz– Surface plasma: 452 nHz

• Conclusion back then:– Sun spins faster in deaper convection zone– Solar dynamo works with d/dr<0: equatorward migr

Yoshimura (1975) Thompson et al. (2003)Brandenburg et al. (1992)

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Application to the sun:Application to the sun:spots rooted at spots rooted at r/Rr/R=0.95=0.95

Ben

evol

ensk

a ya,

Hoe

kse m

a,K

o sov

iche

v, S

c her

rer

(199

9)

nHz 473/360024360

/7.14

ds

do

o

–Overshoot dynamo cannot catch up

=AZ=(180/) (1.5x107) (210-8)

=360 x 0.15 = 54 degrees!

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Arguments against and in favor?Arguments against and in favor?

• Flux storage• Distortions weak• Problems solved with

meridional circulation• Size of active regions

• Neg surface shear: equatorward migr.• Max radial shear in low latitudes• Youngest sunspots: 473 nHz• Correct phase relation• Strong pumping (Thomas et al.)

• 100 kG hard to explain

• Tube integrity

• Single circulation cell

• Turbulent Prandtl number

• Max shear at poles*

• Phase relation*

• 1.3 yr instead of 11 yr at bot

• Rapid buoyant loss*

• Strong distortions* (Hale’s polarity)

• Long term stability of active regions*

• No anisotropy of supergranulation

in favor

against

Tachocline dynamos Distributed/near-surface dynamo

Brandenburg (2005, ApJ 625, 539)

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Origin of sunspotOrigin of sunspot

Theories for shallow spots:Theories for shallow spots:(i) Collapse by suppression(i) Collapse by suppression

of turbulent heat fluxof turbulent heat flux(ii) Negative pressure effects(ii) Negative pressure effects

from <from <bbiibbjj>-<>-<uuiiuujj> vs > vs BBiiBBjj

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clockwise tilt(right handed)

left handedinternal twist

Build-up & release of magnetic twistBuild-up & release of magnetic twist

New hirings:New hirings:• 4 PhD students4 PhD students• 4 post-docs (2yr)4 post-docs (2yr)• 1 assistant professor1 assistant professor• 2 Long-term visitors2 Long-term visitors

Upcoming work:Upcoming work:• Global modelsGlobal models• Helicity transportHelicity transport• coronal mass ejectionscoronal mass ejections• Cycle forecastsCycle forecasts

Coronal mass ejectionsCoronal mass ejections

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Cycle Cycle dependencedependence

of of (r,(r,))

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SunspotsSunspots

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How deep are sunspots rooted?How deep are sunspots rooted?

• Solar activity may not be so deeply rooted• The dynamo may be a distributed one• Near-surface shear important

Hindm

an et al. (2009, ApJ)

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Near-surface shear layerNear-surface shear layer

Benevolenskaya, Hoeksema, Kosovichev, Scherrer (1999)

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Flux emergence:Flux emergence:observations & simulationsobservations & simulations

Hindman et al. (2009, ApJ) Brandenburg (2005, ApJ)

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Flux emergence: simulations and modelsFlux emergence: simulations and models

• Active regions from an instability• Suppression of turbulent motions• Cooling, contraction, field amplification

in preparation withKleeorin & Rogachevskii

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Winter School 11-22 JanuaryWinter School 11-22 January

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