This document discusses findings from the Hinode satellite mission regarding magnetic fields. It summarizes that Hinode discovered: 1) A local convection-driven dynamo process that amplifies weak magnetic fields below equipartition levels to strong kG fields. 2) Transverse waves propagating along magnetic flux tubes, providing evidence of Alfven waves carrying significant energy. 3) Phase differences between magnetic and velocity fluctuations that identify the waves as Alfven and help determine propagation direction.

1. What could Hinode
results tell us
about cosmic
magnetic fields?
1
Saku Tsuneta
Institute of Space and Astronautical Science, JAXA
ISAS Astrophysics Colloquia
2015 February 26 11-12am

2. EUV Imaging
Spectrometer（EIS）
Solar Optical
Telescope（SOT）
X-ray Telescope
（XRT）
Japan-US-UK-ESA project
Orbit: Polar Sun Synchronous
Launched 2006 Autumn
Satellite Hinode (JAXA SOLAR-B)
2

3. EUV Imaging
Spectrometer（EIS）
Solar Optical
Telescope（SOT）
X-ray Telescope
（XRT）
Hinode mission objective:
Systems approach to understand
generation, transport and ultimate
dissipation of solar magnetic fields with
3 well-coordinated advanced telescopes.
Japan-US-UK-ESA project
Orbit: Polar Sun Synchronous
Launched 2006 Autumn
Satellite Hinode (JAXA SOLAR-B)
3

4. Too-strong Magnetic field in the Universe
How does Universe create such strong fields?
• Early universe: 10-21G?
• Galaxies and Clusters of Galaxy: 10-6 G
• Late type stars 103G
• Bottom of convection zone 105 G
• Pulser 1012G
• Magnetor 1015 G
4
Fossil or Compressive process?
Dynamo?
global dynamo?
Local (turbulent) dynamo?

5. Too-strong Magnetic field in the Universe
How does Universe create such strong fields?
• Early universe: 10-21G?
• Galaxies and Clusters of Galaxy: 10-6 G
• Late type stars 103G
• Bottom of convection zone 105 G
• Pulser 1012G
• Magnetor 1015 G
Fossil or Compressive process?
Dynamo?
global dynamo?
Local (turbulent) dynamo?
Dynamo+?
Dynamo+compression
Dynamo+?
Dynamo
Compression and fossil?
needs dynamo
needs dynamo
Compression and fossil
Any dynamo mechanism can amplify the magnetic fields
upto equi-partition fields Be
But not beyond! We sometimes need a mechanism to go
beyond the equi-partition fields.
Kinetic
Energy
Magnetic
Energy
2
2
2
1
8
ru
p
»eB
5

6. l 1.4 GHz
lVLA
Galactic center Solar corona
Does nature prefer flux tubes?
i.e. Does nature prefer higher magnetic energy state?6
Courtesy of Sofue
NASA TRACE

7. 7
l 300 MHz
lStrong magnetic field of mG
lMuch smaller than equi-partition field corresponding
to the local gas
lEquivalent to equi-partition field corresponding to
galactic rotation (100-200 km/s)
Courtesy of Sofue
Galactic center：flux tubes? vertical to the G-plane

8. 8

9. 9
Emergenceofmagneticfields
inaformofslenderfluxtubes
WithBaroundequi-partition

10. Magnetic fields have a form of flux tube
Strong kG magnetic
field in between
convection cells
exceeding equi-
partition B
10

11. 11
1000km

12. 12
Hinode highest resolution
Stokes-V map
(vertical component of B)
Does nature prefer
isolated flux tubes?
1000km

13. Ishikawa+09
Distribution function of
magnetic field strength
Peaks at 1.5kG
Super-equipartition
majority:below500G
Sub-equipartition
Two components
13
Hinode result
Equi-partition
field strength

14. 14
Sub-equipartition B
500G
Super-equipartition B
2000G
200 sec
Formation of super equipartition from
sub-equipartition magnetic fields
Parker prediction：supersonic down flow associated with
thermal instability results in compression of magnetic fields
Nagata+08

15. Convection plus weak magnetic fields result in
strong magnetic fields
Parker (1978); Hasan (1985), Hasan et al. (2003), Bunte, Hasan,Kalkofen, (1983)
G4004
2
1
8
2
2
»»
»
upr
ru
p
B
Be
kG21
8
2
-»
=+
B
PBP ei p
Magnetic
Flux tube
Solar
surface
Convection
flow
Downflow
Inside flux tube
15
15
Sub-equipartition B Super-equipartition B
Inhibit thermal
energy due to B
Cooling and
downflow
Stronger B due
to lateral P balance

16. Ishikawa+08
Convective collapse creates1.5kG flux tubes
(This is not dynamo)
Convective collapse!! 500G 1.5kG
Smaller total B
energy
Larger total B
energy
Peak at 1.5kG
due to convective
collapse
90% is below 500G
Just born?

17. Higher T.
Lower T.
Reduce heat
Input from below
Lateral heat input
from side
Slender flux tube
You are looking at
deeper layer due to
magnetic pressure
Dark sunspot and bright faculae
Emission
From hot wall Solar surface is a
rias coastline due to
thin flux tubes. It
serves as heat sink.
17
Same temperature

18. Sun as seen in UV
Bright faculae
Dark sunpsot
18

19. 0.1-0.2％
Non-constant solar constant
Faculae (slender flux tubes win)!
Solarconstant
year
amplitude of 0.1-0.2%

20. Vertical magnetic fluxHorizontal magnetic flux
Quiet Sun magnetic fields

21. Ubiquitous linear polarization patches
Lites+08, Orozco+07,08, Centeno+08
Ishikawa+08, 09, 10,11ab, Jin+09,
Martınez Gonzalez+09 etc, Danilovic+10
Wherever convection, horizontal fields exist!?
250000km
120000km
Lites+08

22. 22
Local dynamo process
discovered with Hinode
Ishikawa & Tsuneta (2008)
Total flux = 10-100 x sunspot
Field strength < equi-partition
Life time < granulation lifetime
Size <granulation size
Horizontal B below
equi-partition
Equi-partition
field strength

23. Discovery of New Dynamo Mechanism
with Hinode
• Differential rotation of
Sun amplifies magnetic
field
北極
南極
Magnetic
field
Convection
Energy
Magnetic
Energy
北極
南極
北極
南極
Rotation
Energy
Magnetic
Energy
Convection cell 1000km Magnetic field
• Convection motion of
plasma amplifies
magnetic field
Sunspot Horizontal fields
Known mechanism Newly discovered

24. 2006 Dec 17 20:00-21:00 UT CaII H broad band filter images taken with Hinode/SOT
Chromosphere more dynamic than expected!
Chromospheric jets and fountain
driven by magnetic force
24

25. 25
KM late type star：
Fully convective
Active corona
Not consistent with
Solar paradigm
Early type star：
No convection zone
No corona
Hayashi track:
Proto star
Convection dominant
Active corona
Differential rotation driven global scale
Dynamo and convection-driven dynamo
T tauri star：
Convection
Fast rotation
Sunspot, wind
Strong X-rays

26. 26
KM late type star：
Fully convective
Active corona
Not consistent with
Solar paradigm
Early type star：
No convection zone
No corona
Hayashi track:
Proto star
Convection dominant
Active corona
Differential rotation driven global scale
Dynamo and convection-driven dynamo
T tauri star：
Convection
Fast rotation
Sunspot, wind
Strong X-rays
Convection
convection-driven local dynamo
rotation⇒Reynolds stress
⇒differential rotation
⇒global dynamo

27. Takeda & Takada-Hidai, PASJ (2011)
• Subaru observations on 24
moderately to extremely metal-poor
late type MS stars
– Probably slowly or non-rotating
stars with global dynamo not
operative
• HeI 1083nm detected for all stars
– High excitation line (19.7 eV)
– Excellent indicator for coronal
&chromospheric activities
– He abundance independent of
metallicity
• Nearly constant EW for all stars
– Corona exists regardless of
metallicity (i.e. age, rotation
period)
• Not driven by global dynamo
Sun
Extremely
metal-poor

28. Neutral universe with
zero magnetic field due
to zero electric current
First stars and
re-ionization
B=1-30μG
B=0G
28
From website

29. Conservation of magnetic flux
29
0)(0)0(
0
=FÞ==F
=
F
tt
Dt
D
How could we make such a strong
magnetic fields currently observed?
Early universe present time

30. )()(,0;0
)(
)(
;)0(
2
2
ttBBt
B
e
Mc
e
p
cv
t
v
en
pn
cBv
t
B
j
en
p
c
Bv
E
e
e
ww
w
r
r
w
w
w
µ===
=
Ñ´Ñ
-´´Ñ=
¶
¶
´Ñ=
Ñ´Ñ
-´´Ñ=
¶
¶
=
Ñ
-=
´
+
じ；式が同じなら解も同
；渦度の誘導方程式
；渦度の定義
；誘導方程式
運動方程式
SimilarityofInductioneq.
andvortexeq.
30
R. Kulsrud, 2005, Plasma physics for astrophysics
Princeton University Press

31. Initial magnetic field strength
after re-ionization epoch
• If baroclinic, vorticity exists and Biermann
battery mechanism works, resulting in
magnetic fields from zero value.
• How large is the magnetic fields?
– r=100kpc, M=1011Mo
– v=3x105 m/s(virial theorem）
– ω∼v/r=10-16 /s
– B∼10-20G!
31

32. • Equi-partition field due to local dynamo OK!
– n=10-3 cm-3
– v=3x105 m/s
– T=100eV (106K)
• Maximum turnover time OK!
– r/v=3x1023cm/3x107cm/s=1016s<<4x1017s （cosmic
life time）
– Since actual Eddy size is smaller than the largest
scale size r taken here, this is a conservative
estimate.
• A potential problem: not organized field
Turbulent dynamo then works to amplify the
small magnetic fields to the current values
32
G10
8
5
2
2
-
»
=
eq
eq
B
v
B
r
p

33. 宇宙は電離しておらず
電流なしのため磁場
ゼロ
第1世代銀河の形成
と宇宙の再電離
B=1μG
B=0G
33
Vortex in proto-galaxy produces magnetic fields as
large as B=10-20G（Biermann Battery）
↓
Hinode: convection-driven dynamo amplifies B
upto B=Beq=10-6G
↓
Global galactic dynamo B>10-6G
From website

34. 34
Galactic magnetic fields
along spiral arms
• Highly organized
• Observed magnetic
fields comparable to
equi-partition field
strength for local
velocity dispersion
• Umag=B2/8π=U(ISM)
• B=10μG
Courtesy of Sofue

35. Discovery of transverse waves along
magnetic field with Hinode (Okamoto et al 2008)
Spicules, coronal rains, and prominece
over an active region
35

36. Transverse Wave along
magnetic field line carrying
substantial amount of energy
Alfven wave
Magnetic fields
gas
Figures Courtesy Joten Okamoto
Polarimetric data provides phase relationship among magnetic,
velocity and intensity fluctuation, confirming transverse MHD
waves (Fujimura, Tsuneta, 2009).
36

37. In-Situ-like observations of
MHD waves in solar photosphere
Field
strength
Stokes-IPhotometirc
Intensity
Stokes-V
• mode of waves
• direction of wave
• propagating or
• standing waves
• properties of flux
• tubes
Observables:
• δInteisnty(t)
• δB/ / (t), δB┴(t)
• δVLOS(t)
• center-to-limb var.
Doppler vel.
37

38. Half of flux tubes show
such clean common peak
Velocity IntensityMagnetic flux
TimeProfilePowerspectra Fujimura&Tsuneta 09
Fujimura&Tsuneta 09

39. Phase difference (deg) Phase difference (deg)
Phase difference (deg) Phase difference (deg)
φB-φV φV-φI(core)
φI(core)-φB φI(cont)-φI(core)
Fujimura&Tsuneta 09
--90deg --90deg
180deg -0 deg
-3-9min
Solid: pores+flux tubes
Dashed: pores
39
Velocity leads magnetic fields
by quarter of waves.
Importance of phase relation
to identify wave mode and direction of
propagation

40. Discovery of Alfven waves from phase
relation between δB and δ v, but almost
stationary waves!
δB- δ v:0 or 180 deg
δB- δ v:90 deg
Significant reflection of upward
waves at photosphere-corona
transition layer
Kink
mode
Sausage
mode
Fujimura&Tsuneta 09

41. Residual Poyning Flux of kink wave
Differential (upward – downward) Poynting flux is
proportional to cos(φB – φv)
An example with low intensity fluctuation
(dI/I=0.3%)
f=0.73, B0=1.7x103 (G), δB＝21(G),
δv=0.059(km/ s), φB−φv=−96˚ giving
ΔF=2.7x106 (erg/ s/ cm2)
f : average filling factor B0 : vertical magnetic field
δB/ δv: root-mean-square transverse magnetic
field/ velocity fluctuation
)cos(
4
vBvB
fB
F ffdd
p
--=D
Fujimura&Tsuneta 09

42. Sunspot number is a good proxy for
magnetic activity of the Sun
11 year cycle of sunspot number from the era of Galileo
42
Year
Sunspotnumber
Maunder minimum Dalton minimum

43. Gradual decrease of solar activity
Mean Sunspot number
1.0
0.0
-1.0 North
South
High latitude average magnetic flux Wilcox
Royal Belgium observatory
西暦
西暦
Reversal of high latitude field
At around solar maximum 43

44. Importance of polar fields to predict future
solar activity (Choudhuri)
N
S
N
S
N
S
Cause
Weak
polar field
Result
Less number
of sunspots
130 rotations in 11 year
▽Ω-dynamo

45. 45ひので

46. 西暦 西暦
Magnetic
Flux (G)
Minus Plus
MinusPlus
Asymmetric north and south poles
Still significant as of now
• Northern flux decreases rapidly
• Southern flux has much slower decrease.
North South

47. Quadruple poloidal fields
(sketch）
QuadrupleBipolar 47

48. N
S
N
N
Bipolar mode Quadruple mode
Bipolar + Quadruple
Strong diffusionWeak diffusion
Sokoloff and Nesme-Ribes1994

49. Anti-Joy’s law due to
quadruple poloidal field
NN
N
S
N S
Bipolar SunQuadruple Sun

50. Anti-Joy’s law AR#11429
signature of quadruple poloidal field?
50
N
N
S
S
NS

51. 51
1950-1990 (Recent normal cycle)
1670-1710 (Maunder minimum)
Smaller number
of sunspots are
located only in
Southern
hemisphere
North
North
South
South
1680 1690 1700 1710 17201680
1950 1960 1970 1980 1990
LatitudeLatitude
+50
-50
Sokoloff and Nesme-Ribes1994
Location of sunspot emergence

52. The dynamo equation
2015/2/26 52
[ ]
operation)in(dynamo)(
1
)(Eq.inductionofcomponent
1
)(Eq.inductionofcomponent
2
2
2
2
ff
f
f
fff
f
f
f
ah
h
BcEA
r
rA
r
vp
r
t
A
BBpoloidal
B
rr
v
rB
r
B
vpr
t
B
BBtoroidal
vvv
BBB
pp
p
p
p
p
p
p
=+ú
û
ù
ê
ë
é
-Ñ=ú
û
ù
ê
ë
é
Ñ×+
¶
¶
Þ
úû
ù
êë
é
-Ñ+ú
û
ù
ê
ë
é
Ñ×=Ñ×+
¶
¶
Þ
+=
+=
S
Bp
Ap
On meridional plane: poloidal
Perpen. to M.P.: toroidal

53. One interpretation
If cyclic phase differs between hemispheres,
Vector
potential
Near-surface higher
turbulent diffusivity
Hotta, Yokoyama, 2010Fast meridional flow

54. Cycle length: 12.6 year！
黒
点
数
西暦年
黒
点
数
Longer cycle period
is also seen just
before Dalton minimum
Dalton minimum
Year
Sunspotnumber
Past 6 cycles (overlaid)
Current cycle
Northern hemispehre
Southern hemisphere
Sunspotnumber
NAOJ solar observatory
More anomaly
of the Sun

55. period∼14yr
period∼13yr
period∼12.6yr
Are we entering
Maunder minimum?
55
NS-asymmetry
N-S asymmetry?
55

56. present
11400yr
4000yr
Sunspot number in the past 11400 years 56

57. 57
“Sports on a Frozen River” by Aert van der Neer
Courtesy: The Metropolitan Museum of Art
The Maunder minimum

58. 58
Rotation
Turbulence
⇒ Differential rotation
Solitary star like the sun has
strong magnetic fields!
⇒Local dynamo
⇒ Global dynamo

59. Role of Magnetic fields
in Stars and Cosmos and Hinode
• Carry energy through waves
• Store energy
• Dissipate stored energy with magnetic
reconnection
• Induce MHD instability and eruptions
• Suppress cross-field transport for mass
and heat
• Suppress convection i.e. energy transport
59