SolarC-Plan A: Unraveling The Origin of the Solar
Magnetic Field
Allan Sacha Brun
Service dʼAstrophysique/UMR AIM,CEA-Saclay• Observational evidences of solar magnetism andcurrent limitations• 3D MHD simulations of the magnetic Sun: what isneeded• The Sun as a star: magnetism, rotation

A.S. Brun, Solar-C Working Group, Tokyo, 03/09/10

Observational Contraints for theSolar Dynamo and their current limitation

Magnetic Solar Cycle 23-24(HAO, SST & Mt Wilson Data)
Regions
Quiet

ActiveSource: Soho5895.9Å Na I
Magnétogramme

Small vs Large Scale Dynamos
Wide range of dynamical scales!
A.S. Brun, Solar-C Working Group, Tokyo, 03/09/10

Solar Internal Rotation
Helioseismology
Results(GONG, MDI, GOLF data)
TACHOCLINE?

SURFACE SHEAR
Base CZ

A.S. Brun, Solar-C Working Group, Tokyo, 03/09/10

Modulation of Differential Rotation Amplitude with Cycle

Courtesy of Ambroz

A.S. Brun, Solar-C Working Group, Tokyo, 03/09/10

Torsional Oscillations

Meridional Circulation
More & more evidence for multi cellular MC
Local
Helioseismology(Haber et al. 2002)-6060

Mitra-Kaev & Thompson 2007

Meridional Circulation
More & more evidence for multi cellular MC
Influence of B
(active region)on MC

Solar Min (1997)

Svanda et al. 2008

(Haber et al. 2002)

See also Hathaway et al. 1996, Gizon 2004, Zhao
& Kosovichev 2004, etc…

Global Helioseismology: G modes
Golf-NG

Great opportunity to detect them!
Allow a much better determinationof tachocline, radiative interior andinner dynamics (fields, shear, rotation)

Only:
15 kg
15 Watt
Low BpsScience cover

So ok formargin left
Multi-channel
Observationsof sodium doublet
Low noise andGranulation vs depthallows detection ofG-modes

First test in Teneriffe

Garcia et al. 2007

G-mode envelope

Polar Flux and Reversal

HinodeTsuneta et al. 2008

75

Monthly average85

No high cadence continuous observations
A.S. Brun, Solar-C Working Group, Tokyo, 03/09/10

No seismology

~90° Phase lag between Poloidal andToroidal Fields

A.S. Brun, Solar-C Working Group, Tokyo, 03/09/10

Dipole vs Quadrupole Amplitude
Key to determine relative amplitude with accuracy
near polar reversals

Brun, Derosa, Hoeksema 2010

What Observations are Missing Today?
Surface Observations (High Temporal Cadence and Spatial Resolution):• Constraining High latitude profile of Meridional Circulation• Constraining High latitude profile of Differential Rotation• Constraining Temperature latitude profile (via TSI)
• Characterizing Magnetic field in high polar region: Continuously no averages• Quantifying exact phasing between poloidal and toroidal field and dominant mode
• Magnetic helicity budget and flux
Deep Observations (through local or global seismology)• Constraining radial and latitudinal profile of MC• Constraining radial and latitudinal profile of Diff Rot including Tachocline• Constraining thermal structure• Detecting gravity modes and sounding the energy production region• Constraining profile of Rotation deep into the interior• Constraining topology and amplitude of primordial field• Link between magnetic helicity, dynamo action and solar activity (flux emergence)• History of angular momentum => stellar physics• Solar dynamo => stellar dynamo => magnetic field

Multi-D Models of the Solar Dynamo and Magnetism

A Theoretical Viewof the Sunʼs Interior
Dynamics

Figure Caption:
0: Turbulent convection (plumes)
1: Generation/self-induction of B field ("alpha-effect")or 1': Tilt of active region, source of poloidal field
2: Turbulent pumping of B field in tachocline
or 2': Transport of B field by meridional flows
in CZ into the tachocline
3: Field ordering in toroidal structures by large scale(radial and latitudinal) shear in tachocline ("omega-effect")3': Surface shear layer, Solar sub surface weather (SSW),
surface dynamics of sun spot?
4: Toroidal field becomes unstable to m=1 or 2 longitudinal
instability (Parker's)
5: Rise (lift) + rotation (tilt) of twisted toroidal structures
6: Recycling of weak field in CZ
or 7: Emergence of bipolar structures at the Sun's surface
8: Internal waves propagating in RZ and possibly
extracting angular momentum
9: Interaction between dynamo induced field, inner (fossil?) fieldin the tachocline (with shear, turbulence, waves, etc...)10: Instability of inner field (stable configuration?)+ shearing via “omega-effect” at nuclear core edge?
Is there a dynamo loop realized in RZ?

What is needed to Constraint Solar Dynamo Theory
Interface vs distributed Dynamo : location of global dynamo
Alpha-Omega vs Babcock-Leighton : choose which models/paradigm, need
to identify transport processes
Key ingredients:• Flow helicity and vorticity => alpha effect vs depth and latitude• Large scale flows: topology, amplitude, variability of meridional
circulation and differential rotation at all latitudes and as deep as possible• Rotation profile: tachocline, radiative interior => angular momentum history• Transport processes (pumping of field, diffusion, advection…)• Large Scale magnetic field topology and amplitude in interior• Relative amplitude poloidal/toroidal, temporal phasing, spatial location• Flux emergence at all latitudes and scales, substructure of active regions• Magnetic helicity budget, how dynamo generated field are build « conserving »Hmag?

Surface Flux Transport models
Strength of polar branch key to constraint dynamo!

Joyʼs Law

BrunDerosa
2010

~ 20°

~ 0°

A.S. Brun, Solar-C Working Group, Tokyo, 03/09/10

2D Mean Field models: Babcock-Leighton
Standard model: 1 cell per hemisphere

Jouve & Brun, 2007 A&A, 474, 239

Check Benchmark international: Jouve et al. 2008, A&A

2D Mean Field models: Babcock-Leighton
Standard model: 1 cell per hemisphere
Phasingof toro/polo

Jouve & Brun, 2007 A&A, 474, 239

2D Mean Field models: Babcock-Leighton
Influence of High Latitude and Deep Counter Cells

Slow down cycle period: For parameter values identicalto 1 cell case, find T=45 yr
T ~ v0-0.35ηt-0.4s00.05
Jouve & Brun, 2007 A&A, 474, 239

instead of 22, possible to get 22

2D Mean Field models: Babcock-Leighton
Influence of High Latitude and Deep Counter Cells
Different
Phasingof toro/polo

Jouve & Brun, 2007 A&A, 474, 239

Convection pattern and magnetic field structure

In Stable zone

Mid depth CZ

VrBphiThe B field is much more organized in tachocline(possessing an antisymmetric profile)
Browning et al. 2006, ApJLToroidal Field in Convection

longitudinal component of B
(Pm=4)

A.S. Brun, Hinode 3rd Science Meeting, Tokyo, 12/01/09

Influence of a Tachocline?
Browning et al. 2006, ApJL

See Juriʼs Talktachocline

We impose a thermal wind in the stable lower zone compatible with a tachocline of shear
maintained by a viscous drag.

Angular Momentum Balance in Presence of BInternal waves
Inner fossil field
Anisotropic turbulence
Brun, Solar Physics, 2004

The transport of angular momentum by the Reynolds stresses remains at the origin ofthe equatorial acceleration. The Maxwell stresses seeks to speed up the poles.

Getting Strong Toroidal Field
Brun et al. 2004

No tachocline:
mixed polarity
no symmetry

CZ
RZ
Large mean field in tachocline

antisymmetric field

Browninget al. 2006

Solar Radiative Interior Dynamics
Brun & Zahn 2006, A&A, 457, 665; Zahn et al. 2007, A&A, 647, 145

Top of radiative zone (shear imposed by convection zone on top of RZ)

Fossil magnetic field

Final State: Ferraroʼs lawof isorotation @ solar age

Interaction between a fossil field and the inward propagation of a latitudinal shear (e.g. thesolar differential rotation)

Hign mNon-AxisymmetricInstabilities of Bpol and Btor

Dynamo In Radiative Interior?
(Spruit 2002, Braithwaite 2006, Zahn et al. 2007)

m=1
Brun & Zahn 2006, A&A

New Results on the Deep Sun

Omega

Extended RZ & realistic stratificationtachocline

Taylor-Proudman Theorem & Thermal Wind
The curl of the momentum equation gives the equation for vorticity ω=:(a)Taylor-Proudman Theorem:
In a stationary state, the ϕ component of (a) can be simplified to:=> vϕ is cst along z
the differential rotation is cylindrical (Taylor columns) and the flows quasi 2-D.

Thermal Wind:
The presence of cross gradient between p and ρ (baroclinic effects) canbreak this constraint (as well as Reynolds & viscous stresses and magnetic field) :Thermal Perturbations

Key to determine inner dynamics and rotation profile => solar cycle

3-D Views of Internal Waves

Vrdensity

We see them in the models, we need to search for them: Key to contrain inner dynamics,
primordial fields topology, angular momentum budget and history, deep rotation profile

Evolution of a Fossil Field in 3-D Radiative/Convective
Interaction between Radiation and Convection/Tachocline
Zones fundamental to determine global solar magnetism androtation history=> Ferraroʼs law still present (Strugarek, Brun, Zahn 2010)

The Sun as a star:magnetism, rotation, dynamo=> Making the link with astrophysical questions

Stellar Magnetism: X Luminosity(ROSAT All Sky Survey, EspaDONS)Good correlation between activity level and surface convection

sunsdwarfs

massives
Observations Narval(J.F. Donati,massive star tau Scorpii )« A-gap »(J. Schmitt, 2003, IAU S219)

ultra-cool star V374 Pegasi

OBAFGKM

Solar Type Stars (late F, G and early K-type)

Noyes et al. 1984
In stars activity depends on rotation& convective overturning time
via Rossby nb Ro=Prot/τ
<RʼHK> =Ro-1 , Pcyc=Prot1.25+/-0.5
Over 111 stars in HK project (F2-M2):
31 flat or linear signal
29 irregular variables
51 + Sun possess magnetic cycle
Wilson 1978
Baliunas et al. 1995

CaII H & K lines , <RʼHK>

Solar Analogs

Petit et al. 2008, MNRAS

Theoretical models: Jouve, Brown, Brun 2010, Brown et al. 2010

ESPADON/NARVALHow Solar-C/Plan A can help solving the Origin of Solar
Magnetism (Dynamo), Structure of the Solar Interior and beyond
With Plan A High Altitude Orbit:• By improving our knowledge of meridional circulation, differentialrotation, transport processes thus constraining three key
ingredients of the solar Dynamo, detection high polar branch of
torsional oscillations• By characterizing magnetic fields, polar reversals, phasing of toro/polo
components, coupling between large scales flow and field• Structure of wind, angular momentum lost
• Sounding the deep interior (tachocline and upper radiative zone) for
flows, maximum field strengths and field topology, thermal structure,
Dynamo in radiative core?
• g-modes detection via global seismology (Golf-NG): sound speed,density, field and rotation profiles down to the core (energy prod region)• The Sun as a star: allow to answer key astrophysical questions:
Angular momentum history, dynamo mechanism, cosmic magnetism