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					- The 6th Solar-B Science Meeting -



        Magnetic Correspondence
    between Moving Magnetic Features
      and Penumbral Magnetic Fields

                  M. Kubo and T. Shimizu

                           ISAS/JAXA
               Moving Magnetic Features (MMFs)
 MMFs magnetic features (MMFs) are decaying process of sunspots.
 Movingare important for understanding small magnetic elements
 moving outward in the zone (moat region) surrounding sunspots.
 (Sheeley visually carry1971, Harvey & Harvey 1973)
 - MMFs 1969, Vrabec away magnetic flux
                                                    Longitudinal magnetogram
   from sunspots in MDI movie.
 Properties of MMFs are examined                    (MDI: high resolution mode)
 by using only longitudinal magnetogram.
 - Total magnetic flux of MMFs with polarity
   same as sunspots is 3-8 times larger than
   - size: less than about 2”
   flux loss of sunspots (Martinez Pillet 2002).

  - horizontal velocity: 0.5 km/s.
   ⇒ Which MMFs are responsible
  - life time: several minutes ~ ten hours
       for decaying the sunspot?
   (Ryutoba et al. 1998, Zhang et al. 2003)

 ⇒ Magnetic field structure of MMFs ?
We compare magnetic field properties of MMFs to sunspot penumbral fields.

 We investigate much            fields carried away MMFs from
We estimate howvector magnetic flux is and motion of from sunspot by MMFs.
 a observation with the Advanced Stokes Polarimeter (ASP) and MDI.
              Isolated MMFs and Non-isolated MMFs
We focus on all magnetic elements with horizontal motion in the moat region.

• We identify magnetic elements isolated from their surroundings
  in the MDI movie by visual inspection (positive: 21, negative: 21) .
  → isolated MMFs (referred to as MMFs by previous authors)

• Most of the moat region other than the isolated MMFs have magnetic
  fields with radial outward motion. → non-isolated MMFs
                                                            MDI:horizontal velocity
                                                      ( local correlation tracking method
     ASP: magnetic flux (z-direction) 180°
       ASP: inclination intensity
             continuum [degree]                        applying for MDI magnetogram )
penumbral outer boundary              (vertical)
                       moat region

                                        90°
                             15"
                                       (horizontal)


                                        0°
degree of polarization < 0.4%          (vertical)       correlation coefficient<0.9
         Difference between isolated and non-isolated MMFs
         vertical   horizontal    vertical

isolated MMFs                non-isolated MMFs
   (positive)
                                 isolated MMFs




                                                 [%]
   [%]




                                    (negative)




            ASP: inclination [degree]                  MDI: horizontal velocity [km/s]

  • Most of the non-isolated MMFs have nearly horizontal magnetic fields.
  • There are both isolated MMFs with vertical and horizontal magnetic fields.
  • Magnetic features can be identified as the isolated MMFs either when
     - they have polarity opposite to the surrounding non-isolated MMFs
     - they have inclination more than about 15˚ different from that of
        the surrounding non-isolated MMFs
  • Difference of horizontal velocity is not large.
                            Uncombed structure at the penumbral outer boundary
Horizontal magnetic fields and relatively vertical fields
are alternately located at the outer boundary of penumbra.

      → uncombed structure
        (fluted structure or interlocking comb structure)

                            along outer boundary of penumbra
                                                                                      Thomas et al. (2002)
ASP: inclination [degree]




                                                               horizontal
                                                                                                  180°
                                                                                                  (vertical)

                                                                                                   90°
                                                                                                  (horizontal)

                                position angle [degree]                                            0°
                             (counterclockwise from West )                                        (vertical)

                                 vertical components                  ASP: inclination [degree]
                                  We find magnetic correspondence between
                               penumbral uncombed structure and isolated MMFs.
                                     ASP: inclination [degree]
distance form penumbral edge



                                ◇: positive MMFs, ×:negative MMFs          outer boundary of moat region
                                                                    180°
                                                                    (vertical)
            [arcsec]




                                                                    90°
                                                                   (horizontal)


                                                                      0°
                                                                     (vertical)
                                     position angle [degree]
                                  (counterclockwise from West )             outer boundary of penumbra

Penumbral uncombed structure                                                Isolated MMFs
                                                                  inclination               polarity
   Vertical components                                             Vertical           same as sunspot
   Horizontal components                                          Horizontal                 both
                     Magnetic field structure of MMFs
    Our observation on magnetic correspondence shows magnetic fields
    structure of MMFs proposed by Thomas et al. (2002) and
    Weiss et al. (2004) is correct for the first time.

 - Isolated MMFs with vertical fields and polarity same as the sunspot.


vertical component                   penumbra      moat region


     sunspot
    (positive)




  These MMFs are detached from the vertical components of
  the uncombed structure. ⇒ contribute to disintegration of the sunspot
                  Magnetic field structure of MMFs
 - Isolated (and non-isolated) MMFs with nearly horizontal fields

horizontal component                 penumbra      moat region
                                                             non-isolated MMFs
     sunspot
    (positive)




 ・These MMFs correspond to concave or convex parts of horizontal
  magnetic fields extended from the penumbra. Such structure can be
  interpreted as a sea serpent-like structure (Harvey & Harvey 1973).

 ・Contribution to the flux loss of the sunspot is not clear for these MMFs.
  - Horizontal fields are detached from the penumbra → contribute
  - Only concave or convex parts move along the horizontal fields
    → not contribute
                   Magnetic flux carried by MMFs
Magnetic flux transport rate () of MMFs is estimated by integrating
magnetic flux that pass the line with same distance from the penumbral edge:

                             = (Bfcosγ)vrL
                                                   MDI
          d                       vr: radial component of horizontal velocity
                    d

         sunspot                                  ASP
                                  B: field strength
                        d         f : filling factor
          d                           (areal percentage of each pixel
                                        occupied by magnetic atmosphere)
                                   : inclination
              L: length


Flux loss rate of sunspot is determined from day-by-day change of its total flux.
 Flux transport rate of MMFs vs. Flux loss rate of sunspot
                                        uncombed structure is extended up to 5"
Flux transport rate of positive MMFs




                                          flux transport rate [1016 Mx/sec]
just outside of uncombed structure
                                                                                              all the positive MMFs

- much larger than that of
                                                                                              all the negative MMFs
  negative MMFs

- about 7 times larger than flux loss
  rate of the sunspot


                                                                              distance form penumbral edge [arcsec]
                                                                                flux loss rate of the sunspot
 • MMFs can carry away sufficient magnetic flux from the sunspot.

 • Only limited part of the MMFs contributes to the flux loss of the sunspot.
  Which MMFs are responsible for decaying the sunspot?
• The isolated MMFs having vertical fields with polarity same as the sunspot
  carry about 1-3 times larger than the flux loss of the sunspot.




                                        flux transport rate [1016 Mx/sec]
                                                                                             inclination < 45˚




Such MMFs alone can be responsible                                          distance form penumbral edge [arcsec]
for decaying the sunspot.
                                                                              flux loss rate of the sunspot

• The isolated and non-isolated MMFs with nearly horizontal fields would not
  contribute to the flux loss of the sunspot.
                             Conclusions
  We find that the isolated MMFs have magnetic correspondence to
  the uncombed structure of the sunspot penumbra.

Penumbral uncombed structure                   Isolated MMFs
                                      inclination              polarity
Vertical components                    Vertical         same as sunspot
Horizontal components                 Horizontal                both

 The isolated MMFs with vertical fields and polarity same as the sunspot
 carry away sufficient flux for the flux loss of the sunspot.




  Only the vertical isolated MMFs with polarity same as the sunspot are
  responsible for the disintegration of the sunspot.
                         Solar-B Observation
 • The magnetic correspondence between penumbra fields and MMFs
   is still investigated only for a regular decaying sunspot.

   Penumbra appears at very early phase of sunspots (pores) in general.
   → When disintegration of sunspot due to MMFs start ?

    We would like to obtain evolution of the magnetic field structure of
    penumbra and MMFs from pores to mature sunspots by using
    continuous vector magnetic field observations of sunspots and MMFs

 • We find most of the moat region is occupied by the non-isolated MMFs.

  What is observed for the non-isolated MMFs with high spatial resolution?
   → The non-isolated MMFs correspond to small magnetic elements
     such as G-band bright points or not ?

Goal for the study of MMFs is to understand the decaying process of sunspots!
              Bipolar MMFs and Unipolar MMFs
MMFs may be influenced by ambient magnetic fields
due to the lack of spatial resolution.

1. When a pair of MMFs is mixed with the ambient magnetic fields,
   MMF with negative polarity has smaller magnetic flux.

2. When inclination of MMF is similar to that of the ambient magnetic fields,
   MMF with positive polarity may not be identified.


                            ambient magnetic fields with positive polarity
                                    (without horizontal motion)
           bipolar MMF




Such an imbalance of the magnetic flux of MMF pairs is frequently observed.
(Ryutova et al. 1998,Yurchyshyn et al. 2001, Zhang et al.2003)

				
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