Polar magnetic fields
and SOLAR-C
Hinode Observations on polar fields

Saku Tsuneta (NAOJ)

What is going on in polar region ?

Source of fast solar wind
Location of global poloidal fields
sink of meridional flow
High speed solar wind
Polar fields
Ulysses

Kitt Peak(McComasetal 2000)(Wang et al)

Cirtain etal

Courtesy Narukage

2007 March 16

South pole is tilted
7 degree toward us.	
SOT FOV

80 deg70 degPolar landscape kG field

Tsuneta etal (2008 in press)

707５	
８0
８５	

Red：vertical
Blue：horizontal
Polar region consistsof same-sign vertical B
with horizontal B

Temporal evolution of kG patcheskG patches have canopy structureLife time 〜10-20 hours
Super Equi-partition & unipolar
Small flux tubes merge to form large patch
Large patch disintegrates to smaller patches

1hr x 5

Stokes-U

Velocity map obtained from Stokes-I
and kG patches (contour)

Relation between flow-field andmagnetic patches are being analyzed.

Horizontal field
PDF comparison withQuiet Sun and Plage region

Tsuneta etal (2008 in press)
Total
Polar region

Ishikawa & Tsuneta (2009, in press)

TotalPlagehorizontal
QSPlagehorizontal
Polar region

Outward
flux
Whatandis inward
the difference
betweenSouthpole:
96.3%：3.7%
quietsunand the polar region?
East limb QS: 50.5%：49.5%
Ito & Tsuneta 2008
PDF64.0%：36.0%
Stokes Q: Local vertical field
West limb QS:(Stokes Q>0.01)
Stokes Q 180 degree
ambiguity was resolved
by using Stokes V.

 Quiet sun has bipolar field, while polar
region is uni-polar.
 Polar region has stronger fields.
 No difference in terms of horizontal fields
Quiet Sun
Quiet Sun

Vertical field (inward)

Polar region

One order of magnitude
higher flux in strong B
regionVertical field (outward)

Courtesy Narukage

Inflation of polar flux tubes nearphotosphere-chromosphere boundary
Higher polar coronal field
due to uni-polarity and higher
Surface B.

All the flux tubes areconnected tointerplanetary space.

Very small fraction of flux
tubes is connected tointerplanetary space.
Figure Courtesy Joten Okamoto

Summary
Properties of polar fields• Vertical field component– PDF with extenstion to super-equipartition (400-500G)
field strength seen as kG patch– kG patch fanning-out structure– Unipolar in contrast to QS– Appear from nothing to disappear to nothing– 10-15 hour life time
– North flux same as south flux

• Ubiquitous horizontal fields component
everywhere as seen in Stokes V– PDF similar to those of quiet sun and plage region– Local dynamo process (Ishikawa and Tsuneta 2009)

Impact to solar dynamo• Magnetic flux is transported to the polar regions withmeridional flows and supergranular diffusion. Fluxtransport would be done via an aerodynamic (drag) force
against magnetic tension force, and may be more difficult
than the case for the mean field case.
• If the flux tubes seen on the surface of the Sun are
maintained inside the Sun, they may affect a known
difficulty in Ω-mechanism to generate intense toroidal
field– an amplification factor of 100 that is needed to explain acombination of 1kG poloidal field with 100kG toroidal field may
be achievable within a solar cycle.
– There remains, however, a serious energetic problem.

Do we need polar missionin terms of B-observations? 	
• What is the difference between QS and polar region?
Further analysis on Hinode is needed.
• We need Stokes-polarimeter for precise measurement
for magnetic fields. High quality ME maps are available
upto latitude of 87 degree, if the sun is 7 degree tilted
toward us.
• If orbital inclination is 15 degree, we can see 12 degree
beyond the pole.
• We should resolve THMFs. Its relationship with global
dynamo is totally unknown. (Is 1 arcsec magnetographfor polar region interesting enough when we are familiar
with Hinode images?	

How far we can see?	
Polar axis is tilted
7 degree toward us.	

12 degree beyond
the pole can be seenfrom inclination of15 degree.	

3 degree from the polecan be seen with Hinode	70	75	
80	

85	

A proposal	• Put B-satellite into plan-A orbit, but with
low inclination of 10-20 degree.
• B-satellite is high-resolution mission.
• In addition to the B-satellite, we shouldhave high-inclination A-satellite via interagency collaboration. Inclination angle
should be optimized by consideringscience drivers and resources.	

Probability Distribution Function of polar field
Stronger Bdominates
Energy PDF

PDF

VerticalbrightTotalVerticalWeaker B
dominates

Horizontal

0500

1000

Magnetic field (G)0500

Horizontal

1000

Magnetic field (G) Continuum intensity

00.5

1.0

Filling factor

Low pressure coronal hole is sustained byhigher magnetic pressure of coronal hole
CH pressure is a factorof 2 (T-diff.) x 3 (n-diff.)= 6 smaller than that ofsurrounding quiet Sun.
This must be balanced
by stronger CH magnetic
field.

1MK

Temperature2007 Feb.17

CH =〜 1.0 MK
QS = 1.5 〜 2.0 MK
XBP> 1.5 MK0Kano et al (2008)

2MK

1234 x108“Density”

CH = 1.0〜1.5 ｘ108 cm-3
QS/XBP = 2〜3 ｘ108 cm-3

Total and average magnetic flux
• Magnetic filling factor: 0.05 < f < 0.35
• Total magnetic flux in a pixel– B x f x pixel size with foreshortening correction• Total magnetic flux in SOT FOV– vertical flux
– horizontal flux

2.2-9.9 x 1021 Mx
0.4-2.0 x 1022 Mx• Horizontal flux factor of 2 larger• Average vertical flux 10.0 G• Total vertical magnetic flux for > 70 degree– 0.6-2.5 x 1022 Mx• Ulysses observations– 2 x 1022 Mx (above 35 degree)Variation of total polar flux over one year
North polar region
South polar region

Ito and Tsuneta, 2008
In prepkG patch (Q>0.005)

Exact balance of north and south total flux
Constant flux over 1 year
Total vertical flux
(Q>0.002)
1 yearWhat is the implication of the kG polar field
for acceleration of fast solar wind

Fast solar wind
comes from here
Flares and jets
8

Polar field extrapolation (potential)
using polar SP data embedded in
MDI data (Shiota, Ito, Tsuneta, 2009)
A factor of 345 inflation of the flux
tubes near photospherechoromosphere-corona boundary

reconnection

Horizontal field

Figure Courtesy Joten Okamoto

Fanning-out kG patch
Chimney for Alfven waves• Uniform magnetic field: Aflven
wave reflection in thephotosphere-corona boundary

coronaLarge VA	
Small VA	photosphere

VA =B√ 4π ρ	• Fanning-out flux tube: serves
as chimney for Alfven waves– more Alfven wave flux that
accelerates fast solar wind istransmitted to the corona due to thefanning-out structure.

Uniform magnetic tube
coronax1000
Small VA	Magnetic trumpetphotosphere-

Stokes Q black polarity=North-Southmagnetic component

Polar flux tube
Fanning-out structure-U+
Unipolar structurein Stokes Q-+V+U-V-Q
Stokes V dominant blackpolarity =magnetic field
away from the Sun+

Bipolar structurein Stokes U & V

Milne-Eddington least-squares fit• To minimize the influence of noise, fitting is performed
for pixels whose Q, U or V signals are larger than 5sigma.
– 10.5% of the area meets the criteria.

• Formation layer at 80 degree latitude is approx. 100 km
above the nominal height.
• ME works fine for the extreme limb!
• Parameters– vector magnetic field (strength, inclination angle, and azimuthangle), the line of sight velocity, two parameters describing thesource function, the line-to-continuum absorption coefficient
ratio, Doppler width, damping parameter, stray light factor(fillingfactor)

minusNE

Stokes-QW
plusplus
Sminus