Magnetic Correspondence Magnetic Correspondence between Moving Magnetic Features between Moving Magnetic Features

and Penumbral Magnetic Fieldsand Penumbral Magnetic Fields

M. Kubo and T. Shimizu

ISAS/JAXA

- The 6th Solar-B Science Meeting -

We investigate vector magnetic fields and motion of MMFs from a observation with the Advanced Stokes Polarimeter (ASP) and MDI.

Moving magnetic features (MMFs) are small magnetic elements moving outward in the zone (moat region) surrounding sunspots.(Sheeley 1969, Vrabec 1971, Harvey & Harvey 1973)

Properties of MMFs are examined by using only longitudinal magnetogram.

- size: less than about 2”

- horizontal velocity: 0.5 km/s.

- life time: several minutes ~ ten hours (Ryutoba et al. 1998, Zhang et al. 2003)

⇒ Magnetic field structure of MMFs ?

MMFs are important for understanding decaying process of sunspots.

- MMFs visually carry away magnetic flux from sunspots in MDI movie.

- Total magnetic flux of MMFs with polarity same as sunspots is 3-8 times larger than flux loss of sunspots (Martinez Pillet 2002).

⇒ Which MMFs are responsible for decaying the sunspot?

We compare magnetic field properties of MMFs to sunspot penumbral fields.

We estimate how much magnetic flux is carried away from sunspot by MMFs.

Moving Magnetic Features (MMFs)Moving Magnetic Features (MMFs)

Longitudinal magnetogram (MDI: high resolution mode)

15"

moat regionpenumbral outer boundary

ASP: continuum intensity ASP: magnetic flux (z-direction)

degree of polarization < 0.4%

180°

(vertical)

90°

(horizontal)

0°

(vertical)

ASP: inclination [degree]

degree of polarization < 0.4%

• 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

Isolated MMFs and Non-isolated MMFsIsolated MMFs and Non-isolated MMFs

MDI ： horizontal velocity ( local correlation tracking method applying for MDI magnetogram )

correlation coefficient ＜ 0.9

We focus on all magnetic elements with horizontal motion in the moat region.

Difference between isolated and non-isolated MMFsDifference between isolated and non-isolated MMFs

• 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.

verticalvertical horizontal[%

]

non-isolated MMFs

isolated MMFs (negative)

isolated MMFs (positive)

[%]

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

ASP: inclination [degree]

Uncombed structure at the penumbral outer boundaryUncombed structure at the penumbral outer boundary

180°

(vertical)

90°

(horizontal)

0°

(vertical)

along outer boundary of penumbra

AS

P:

incl

inat

ion

[deg

ree] Thomas et al. (2002)

Horizontal magnetic fields and relatively vertical fields are alternately located at the outer boundary of penumbra.

→ 　 uncombed structure　　　 (fluted structure or interlocking comb structure)

vertical components

position angle [degree](counterclockwise from West )

horizontal

We find magnetic correspondence between penumbral uncombed structure and isolated MMFs.

dist

ance

for

m p

enum

bral

edg

e [a

rcse

c]

90°

(horizontal)

ASP: inclination [degree]

Isolated MMFs

inclination polarity

Vertical components Vertical same as sunspot

Horizontal components Horizontal both

position angle [degree](counterclockwise from West )

Penumbral uncombed structure

outer boundary of penumbra

180°

(vertical)

outer boundary of moat region

0°

(vertical)

◇: positive MMFs, × ： negative MMFs

Magnetic field structure of MMFsMagnetic 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.

penumbra moat region

sunspot(positive)

vertical component

These MMFs are detached from the vertical components of the uncombed structure. ⇒ contribute to disintegration of the sunspot

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

non-isolated MMFs

Magnetic field structure of MMFsMagnetic field structure of MMFs

penumbra moat region

- Isolated (and non-isolated) MMFs with nearly horizontal fields

・ 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

horizontal component

sunspot(positive)

vr: radial component of horizontal velocity

B: field strengthf : filling factor　　 (areal percentage of each pixel occupied by magnetic atmosphere) : inclination

Magnetic flux carried by MMFsMagnetic 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

sunspot

L: length

dd

d

d

MDI

ASP

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 sunspotFlux transport rate of MMFs vs. Flux loss rate of sunspot

all the positive MMFs

all the negative MMFs

uncombed structure is extended up to 5"

• MMFs can carry away sufficient magnetic flux from the sunspot.

• Only limited part of the MMFs contributes to the flux loss of the sunspot.

Flux transport rate of positive MMFsjust outside of uncombed structure

- much larger than that of negative MMFs

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

flux loss rate of the sunspot f

lux

tran

spor

t ra

te [

1016

Mx/

sec]

distance form penumbral edge [arcsec]

Which MMFs are responsible for decaying the sunspot?Which MMFs are responsible for decaying the sunspot?

flux loss rate of 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.

Such MMFs alone can be responsible for decaying the sunspot.

• The isolated and non-isolated MMFs with nearly horizontal fields would not contribute to the flux loss of the sunspot.

inclination < 45˚

flu

x tr

ansp

ort

rate

[10

16 M

x/se

c]

distance form penumbral edge [arcsec]

ConclusionsConclusions

Only the vertical isolated MMFs with polarity same as the sunspot are responsible for the disintegration of the sunspot.

We find that the isolated MMFs have magnetic correspondence to the uncombed structure of the sunspot penumbra.

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

Penumbral uncombed structure Isolated MMFs

inclination polarity

Vertical components Vertical same as sunspot

Horizontal components Horizontal both

Solar-B Observation

• The magnetic correspondence between penumbra fields and MMFs is still investigated only for a regular decaying sunspot.

Goal for the study of MMFs is to understand the decaying process of sunspots!

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 usingcontinuous vector magnetic field observations of sunspots and 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 ?

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

Bipolar MMFs and Unipolar MMFsBipolar MMFs and Unipolar MMFs

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)

bipolar MMF

ambient magnetic fields with positive polarity (without horizontal motion)

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.