Evolution of magnetic fields at the boundary of the penumbra

1
Evolution of magnetic fields at the boundary of
the penumbra

• Masahito Kubo (HAO/NCAR),
• K. Ichimoto2, T. Shimizu3, B. W. Lites1, S.
  Tsuneta2,
• Y. Suematsu2,Y. Katsukawa2, S. Nagata4,
• T.D. Tarbell5, R.A. Shine5, A.M. Title5,
• A. G. de Wijn1, and Hinode/SOT team

(1) HAO/NCAR, (2) NAOJ, (3) ISAS/JAXA, (4) Kyoto.
U, (5) LMSAL
2
Outer boundary of penumbra

• Dynamical motion of penumbral fine structures
• Many small magnetic features called moving
  magnetic features
• (MMFs, Harvey Harvey 1973) move outward from
  the penumbra.
• MMFs have magnetic correspondence with penumbral
  fields (Kubo et al 2007).

G-band
LOS magnetic field
3
Penumbral fields and MMFs
MMFs outside the horizontal component of
penumbral fields
penumbra
moat region (outside of the sunspot)
Uncombed penumbra
Vertical component
Evershed flow
Horizontal component
penumbra
moat region
MMFs

• Continuation of penumbral horizontal fields
• (Sainz Dara Martinez Pillet 2005, Kubo et al.
  2007 submitted.)
• ? Fluctuation of penumbral horizontal fields
  (Schlichenmaier 2002)
• Evershed flows (clouds) become the MMFs (Cabrera
  Solana et al. 2006)
• ? The outward motion is driven by Evershed flows.

4
Penumbral fields and MMFs
MMFs outside the vertical component of penumbral
fields
penumbra
moat region (outside of the sunspot)
Uncombed penumbra
Vertical component (spine)
penumbra
moat region
MMF

• Vertical fields with polarity same as the
  sunspot
• ? A result of the detachment of the vertical
  component of the penumbra
• More important for sunspot decay
• Formation process??

5
SOT/SP observation
Continuum intensity
Vertical component of Penumbral fields (spine)
We investigate whether the relation between the
bright features in the outer penumbra and the
vertical MMFs is general or not by using FG
observations.
Bz (z LOS) KG
1
-1
MMF
The bright features appeared in the outer
penumbra is a key phenomenon for the formation
of the vertical MMF with polarity same as the
sunspot (Kubo et al. 2007 submitted to PASJ
Hinode Special Issue).
6
SOT/FG observations large FOV with good time
resolution

• Wavelength
• - Broadband Filter Imager (BFI) G-band, Ca II
  H
• - Narrowband Filter Imager (NFI) LOS magnetic
  field in the photosphere
• 
  with Stokes IV mode of 6302(_at_-120mA)
• Pixel scale
• 2 x 2 summing (BFI 0.109/pixel, NFI
  0.160/pixel)
• 2minutes cadence for 8 hours
• (2007/01/04 1614 2358)
• The stability for long duration is much
• better than ground-based observations.
• Sunspot location X-204, Y - 15
• Line-of-sight vertical to the solar surface

G-band
7
Radial distance Position angle diagram
East (limb-side)
West (center-side)
South
moat region
radial outward
penumbra
90
G-band
15

• The G-band image averaged over 8 hours is used
• to define the penumbral outer boundary and the
• sunspot center.
• The sunspot center is determined by the center
  of
• gravity for darkness of the sunspot.

0
0
180
360
270
8
How to see NFI magnetogram
LOS magnetogram (NFI)

• Intense white/black areas
• ? Vertical magnetic field
• (white positive polarity)
• Gray areas
• ? Horizontal magnetic field
• (Not non-magnetic area)

2007/01/04 1912
Inclination angle (SP)
2007/01/04 1840 -1943
Inclination
positive
negative
9
G-band vs. LOS magnetic fields

• MMFs with polarity same
• as the sunspot separate
• from the elongated spines.
• The outer boundary of
• penumbra is fluctuated.
• - Dark penumbral filament
• ? outside the penumbra
• - Granules in the moat region
• ? inside the penumbra

distance to penumbral edge arcsec
position angle (counterclockwise from west)
degree
White positive, Black negative in LOS
magnetogram (NFI)
10
G-band vs. LOS magnetic fields

• Bright features in the
• outer penumbra are
• located at the spines.
• While the MMFs are
• separating from the spines,
• the granules in the moat
• region enter the penumbra.

distance to penumbral edge arcsec
granule in the moat
MMF
position angle (counterclockwise from west)
degree
bright feature
contour bright features in G-band image
spine
11
Temporal change of penumbral outer boundary
(inside)
G-band (BFI)
-2 to the penumbral edge
Bright features crossing the green line come
from the moat region or appear in the outer
penumbra.
Time - Position angle diagram along the green line
12
Temporal change of penumbral outer boundary
(inside)
LOS magnetogram (NFI)
-2 to the penumbral edge
Magnetic features crossing the green line are
mostly the elongated spines or the MMFs
detached from the spines in the limb-side
penumbra
Time - Position angle diagram along the green line
13
Temporal change of penumbral outer boundary
(inside)
G-band (BFI)

• The bright features
• in G-band image
• are generally located
• at the elongated spines
• (or the detached MMFs).
• These is no bright
• feature at the center of
• the large elongated spine
• and the large MMFs.

LOS magnetogram (NFI)
contour bright features in G-band image
14
Temporal change of penumbral outer boundary
(outside)
G-band (BFI)

• 1 to the penumbral edge
• the moat region just
• outside the penumbra

LOS magnetogram (NFI)
15
Temporal change of penumbral outer boundary
(outside)
G-band (BFI)
The dark penumbral filaments elongating to the
moat region - horizontal fields -
surroundings of the MMFs
LOS magnetogram (NFI)
contour dark features in G-band image
16
Summary

• The bright features in the outer penumbra are
  generally located at
• the elongated spines or the MMFs detached from
  the spines.
• ? The convection motions around the penumbral
  outer boundary
• are responsible for the disintegration of
  the sunspot.

hot gas in the outer penumbra

• The formation of the vertical MMFs with polarity
  same as the sunspot may
• be related to the dark penumbral filaments
  elongating to the moat region.

17
Thank you for your attention!
18
G-band vs. Blue continuum
The G-band bright features in the penumbra are
also bright in the blue continuum images.
distance to penumbral edge arcsec
position angle (counterclockwise from west)
degree
contour bright features in blue continuum
19
Ca II H vs. LOS magnetogram
The Ca II H bright features are located at the
MMFs.
distance to penumbral edge arcsec
Upper LOS magnetogram (NFI) Lower Ca II H (BFI)
position angle (counterclockwise from west)
degree
contour bright features in Ca II H image