The Science for Plan -A

Why dynamo in Solar-C plan-A ?
T. Yokoyama(Univ. Tokyo)

What is our standpoint now ?
We have learned (been learning) much about the plasma
dynamic phenomena strongly coupled with the magnetic
evolutions on the surface of the Sun by Yohkoh, Hinode,other spacecrafts', and ground-based observations.
The origin and the maintenance of the magnetic fields might
be one of the most interesting issues which we should
address next.

What is the background for the appearance of thedynamo as an important subject of Solar-C/a ?
Theoretical pictures of the dynamo have been establishedbased on the helioseismic observations in this a few
decades. The roles of the tachocline and the meridional
flow is becoming more and more important. (e.g.
Charbonneau 2005)
The simulation studies have made clearer the mechanisms
for sustaining the differential rotation and meridionalflows. (e.g. Rempel 2005, Miesch et al. 2005)
The local helioseismological technique gave more new
information on the local structures of the interior. (e.g.
Zhao et al. 2001)

from Astrophysical point of viewDynamos in astrophysical objects– Stellar dynamos :– Accretion disk dynamo: The magnetic field plays a role to sustain
a turbulent angular momentum transport (through the MRI)
leading to the accretion of the matter into the central object, suchas a black hole.
– Magnetar: It is believed that the several orders of magnitude
stronger magnetic field of magnetars beyond the ordinary pulsars
are generated by the dynamo effect during its generation at thesupernova period.
– Gamma ray bursts, galactic dynamo etc.

Stellar cycle

25yrs

12yrs

Hall (2008, Living Rev. Sol. Phys.)The important issues in solar physics– Flares, CMEs
• The "standard picture" is established based on many S/Cs'
observations including Yohkoh. (Particle acceleration issue isstill a remained homework...)– Coronal heating• This should be solved by Hinode.
– Dynamo• Much progress has been achieved by SOHO etc. but stillopen.

Issues related with the dynamo to be addressedin Solar-C/aNote
Solar dynamo theory is still " fragile " (by A. Title ?).
– (following is my personal interpretation ...)

There does not exist a theoretical perfect model which
describes all of the observational aspects. So we should
not expect that "some key observations" may solve thedynamo issues.
However, any information on polar observations by plan-A
may greatly advance the dynamo science.

Issues to be addressed in Solar-C/a (1/2)
Meridional flow
– What is the flow pattern/speed near the poles ? Especially thelatitude of the flow sink is of much interest.
– Solar cycle variability.
– Flows in the interior. What is the depth of the return flow ? Is it asingle-cell flow ?

Differential rotation– Omega distribution in the poles– ΔT as a function of latitude: Source of the non-Taylor-Proudman
rotationIssues to be addressed in Solar-C/a (2/2)
Polar surface magnetism– Cycle polar-field reversal– magnetic flux budget– magnetic submergence ?

Flux tube in the overshoot layer– Does it anyway exist ? (10^(-5) anomaly)– Where in latitude ? Do they show variability ?
– What is the structure, tubes, sheets or else ?

Rotating flow in a troidal tube
– 200m/s flow is expected to keep the dynamical equilibrium– in the emerging phase on the way up to the surface

Conclusion
Solar dynamo is our frontier !
This is the reason why we should go.