SOLAR-C Plan A
Helioseismology
and dynamo science
Takashi Sekii
andSOLAR-C HSD sub-WG

 The main scientific target is

Observational studies ofthe solar dynamo processes
By helioseismology andother measurements

NAOJ
SOLAR-C SDM2 9 March 2010

The HSD sub-WG

The HSD sub-WG

 Helioseismology and the Solar Dynamo(HSD) sub-WG

 Mission

 Appourchaux (co-chair), Birch, Braun, Brun,Charbonneau, Gizon, Hara, Kosovichev,
Leibacher, Miesch, Rempel,p Schuessler, Sekii(co-chair), Toomre, Yokoyama, Zhao

SOLAR-C SDM2 9 March 2010

 What are the outstanding issues in ourunderstanding of the solar dynamo
mechanism? (Brun)y Plan-A
 How do we address them byhelioseismology (ad other) observations?
(Kosovichev)
 How does Plan A compare with other ‘similar’
missions (Appourchaux, Kosovichev)

SOLAR-C SDM2 9 March 2010

The solar dynamo

The solar dynamo

 The 11-yr solar activity cycle is thought
to be driven by a dynamo mechanism

 The 11-yr solar activity cycle is thought
to be driven by a dynamo mechanism

 i.e. interaction between magnetic field andplasma flow

 i.e. interaction between magnetic field andplasma flow

Dikpati & Gilman (2006)
SOLAR-C SDM2 9 March 2010

SOLAR-C SDM2 9 March 2010

1

The solar dynamo

The solar dynamo

 We have had some success But the full understanding is still far away

 A flux-transport dynamo model by Dikpati
and Gilman (2006)
 Successfully ‘predicted’ cycles 16-23 using
data from p
precedingg cyclesy Kinematic theories (such as Dikpati & Gilman
2006) assumes the flow structure Aside from some physical questions…
 the extremely
y low activityy at the beginning
gg of thecurrent cycle was predicted by nobody

 Both theoretical and observational
approaches are required to advance ourknowledge
 How do we observe the solar interior?

Dikpati & Gilman (2006)
SOLAR-C SDM2 9 March 2010

SOLAR-C SDM2 9 March 2010

Helioseismology

Helioseismology

 Probing the solar interior using waves
 Equilibrium thermal structure Solar differential rotation

 Can be modelled Solar internal flow

Surface shear layer
Non-columnar rotation

 Can be modelled too?

 Reynolds number > 1010
 Kolmogorov’s law: dof per dimension~1010×3/4
 For the 3-d case dof > 1022…TOUGH!

 Helioseismology is more important formeasuring flows
SOLAR-C SDM2 9 March 2010

Helioseismology‘Tachocline’
Rigid rotation?

Thompson et al (1996)
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What are the issues?

 Meridional flow

 Poleward, up to 20m/s

Giles et al (1997)
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What are the issues?

What are the issues?

 Location of dynamo

 Magnetic field transport Wavespeed anomalies due to magnetic field,or flows induced by the magnetic field Tachocline?

 Difficult to detect as a wavespeedpanomalyy ((highg β)
 ~102 m/s flow? Maybe possible to detect Sekii@SDM1: “in the realm of possibility,depending on exactly magnetic field strength
and width”

SOLAR-C SDM2 9 March 2010

 Magnetic buoyancy, meridional flow andturbulent transport
 Meridional flow in high-latitude region
 Meridional counter flow?
 Probably ~100 m/s flow. Extremely difficult

 Turbulent transport Can we measure diffusivity?

 Rising flux tubes?

SOLAR-C SDM2 9 March 2010

What should be observed?

What should be observed?

 Global flows

 High-latitude magnetic fields

 Differential rotation/torsional oscillation athigh latitudes
 Polar vortex?
 Tachocline

 Poloidal field regeneration (‘α effect’) Helical flow?
 Magnetic helicity

SOLAR-C SDM2 9 March 2010

 There are many aspects:

 Energy & flux budget of dynamo
 Multi-polar structure of the mean poloidal field Efficiency of Babcock-Leighton
 Magnetic helicity
 Magnetic effect on rotation inversions?

 But to summarize

 To see interplay of flows and magnetic fields THERE

SOLAR-C SDM2 9 March 2010

What should be observed?

How do we observe?

 The main goals:

 Global helioseismology?

 Helioseismic measurement of various flows in the high-latitude region
 the tachocline region

 The ppolar magneticg
field

SOLAR-C SDM2 9 March 2010

 Rotation at high-latitude inaccessible toglobal helioseismology because of thestructure of global eigenfunctions
 Meridional flow also inaccessible to global
ghelioseismology (in the linear regime)
 Tachocline structure: yes unless a feature is
too localized. Would it be localized?

SOLAR-C SDM2 9 March 20103

How do we observe?

How do we observe?

 Local helioseismology?

 Difficult because…

 Can observe high-latitude flows i.e. nolimitation due to eigenfunctions but…
 Can observe localized tachocline feature if we
can catch 45-degree
gskip
p rays,y , but…
 it is difficult from within the ecliptic plane
because of…
 foreshortening projection

SOLAR-C SDM2 9 March 2010

 Foreshortening： loss of spatial resolution
 Travel time poorly defined for a pixel pair

 Projection： Doppler velocity S/N degradation
 Convective noise p
predominantly
y horizontal

 We can alleviate these problems by Observing from above

SOLAR-C SDM2 9 March 2010

How do we observe?

How high should we go?

 Local helioseismology from high latitudes
is the only way Why we might think 30 deg is sufficient Meridional flow can be measured from theecliptic plane up to 60 degree latitude
 60+30=90

 Why we would be wrong

 Among other issues, the longitudinal range
over which we can average = cosφ

 cos 60°= 0.5, cos 80°= 0.174, cos 85°= 0.09

 We need to go to (30+α) latitude

 Also to ensure substantial observing time

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SOLAR-C SDM2 9 March 2010

Helioseimology observations

Polar flows by Hinode/SOT There are two main modes Nagashima (2010)

1. High-latitude local helioseismology
 Repeat what we do at lower latitudes
 Can do it solo

2. Two-vantage-pointg p‘largeg angle’ghelioseismology
 More challenging
 Needs a partner

SOLAR-C SDM2 9 March 2010

 Time-Distance method
Supergranular pattern

Rotation & Meridional flow

SSomethingthiinterestingi tti
is definitely going on here

SOLAR-C SDM2 9 March 20104

A very high-resolution telescope?

Observational study of dynamo

 Q. Would that do the job for Plan A?
 A. Partly but not entirely Helioseismology

 We are not yet in position to discuss a few‘key observations’ that would pin down
the dynamo theory

 Magnetic-field measurement

 It is the time for studying SCZ dynamics ingeneral, as an observational approach tothe solar dynamo Doppler measurement is preferred: we need a highinclination orbit
 A decent FOV is required for probing deeper: a bigtelescope would not have it
 The issue of vertical vs. horizontal components: it
would offer complementary view
 Spatial & temporal coverage
SOLAR-C SDM2 9 March 2010

 Theory not mature yet The polar region is by far the least
investigated so far

SOLAR-C SDM2 9 March 2010

Conclusions
 SOLAR-C Plan A will provide important
observational constraints on the solar
dynamo/SCZ dynamics

 Local helioseismology from an inclined orbit
is the key
 …and the polar magnetic field measurement

SOLAR-C SDM2 9 March 20105