Source and fate of the Sun

1
Source and fate of the Suns magnetic helicity

• Magnetic helicity conservation
• Measuring it quantitatively
• Connection with the dynamo
• Axel Brandenburg (Nordita, Stockholm)

2
Magnetic helicity
3
Its a popular logo too
4
Magnetic helicity conservation
How J diverges as h?0
Ideal limit and ideal case similar!
5
Helicity in Magnetic Clouds
From fits to a linear force-free field
Lynch et al. (2005)
6
Helicity from time series
Matthaeus et al. (1982)
7
Coronal mass ejections from helical structures
Gibson et al. (2002)
8
(No Transcript)
9
Nindos et al. (2003)
10
Nindos Andrews (2004)
11
Current helicity and magn. hel. Flux
Bao Zhang (1998), neg. in north, plus in
south (also Seehafer 1990)
Berger Ruzmaikin (2000)
S
DeVore (2000)
N
(for BR CME)
12
Sigmoidal filaments
(from S. Gibson)
13
No helicity production by flowsbut segragation
in space
Generates toroidal from poloidal field
Hlt0
Poloidal field regenerated by tilting (Coriolis
force)
Hgt0
14
Twisting an existing tubesegragation in
spectral space
15
Cancelling magn helicityintroduced in single tube

-
16
a-effect dynamos (large scale)
New loop
Cyclonic convection Buoyant flux tubes
Differential rotation (prehelioseism faster
inside)
Equatorward migration
? a-effect
?need meridional circulation
17
Tilt ?? pol. field regeneration
standard dynamo picture
N-shaped (north) S-shaped (south)
? internal twist as dynamo feedback
18
Production of large-scale helicity
forcing produces
and
But no net helicity production
therefore
? alpha effect
Yousef Brandenburg AA 407, 7 (2003)
19
Saturation 50 energy in large scales
azimuthally averaged
no helicity, e.g.
Rogachevskii Kleeorin (2003, 2004)
geometry here relevant to the sun
neg helicity (northern hem.)
Brandenburg (2005)
20
Simulations forced turbulence w/shear
Negative current helicity net production in
northern hemisphere
1046 Mx2/cycle
Brandenburg Sandin (2004, AA 427, 13)
Helicity fluxes from shear Vishniac Cho (2001,
ApJ 550, 752) Subramanian Brandenburg (2004,
PRL 93, 20500)
21
Connection with a effect writhe with internal
twist as by-product
a effect produces helical field
W
clockwise tilt (right handed)
? left handed internal twist
both for thermal/magnetic buoyancy
22
Scaling with Rm in a mean-field model
with S Cancelaresi and P Chatterjee arXiv0905.024
2
23
Conclusion

• A.B important output of dynamo
• Dynamo (SS vs LS)
• Problems
• a-quenching
• slow saturation
• Solution
• Modern a-effect theory
• j.b contribution
• Magnetic helicity fluxes

1046 Mx2/cycle