Moving Magnetic Features as Prolongation of Penumbral Filaments

The Astrophysical Journal, 632:1176-1183, 2005 October 20

. Sainz Dalda 1Telescope Heliographique pour l'Etude du Magnetisme et des Instabilites Solaires (THEMIS), Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain; asainz@themis.iac.es and V. Martinez Pillet Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain; vmp@iac.es

Ⅰ. INTRODUCTION

Main products of this paper: Establish a clear connection between penumbral field lines, magnetic filaments in the moat region, and the bipolar MMF activity

Brief review of previous works:(1)penumbra

Title et al. (1993) Fluted penumbral magnetic structures

Fluctuations of mag.field inclination: ±18°

Lites et al(1993) two structures: more vertical:stronger m.f. (spines) more horizontal:weaker m.f. (intraspines)

Other recent works of penumbra:

Bellot Rubio et al. (2004):

(1) Tubes carrying the Evershed flow: ・ horizontal at a radius of 0.8 times sunspot radius ・ mean inclination of 115°at the outer penumbral boundary

(2) Spine components: ・ inclination of 60°at the outer penumbral boundary

Theoretical model of penumbral fine structures(Schlichenmaier 2002)

Principle of a Siphon flow (from

(2) MMF

・ Harvey & Harvey (1973): detached field lines from the decaying sunspot

Harvey & Harvey (1973)?

・ Martinez Pillet (2002): a net flux of moat flow > 3-4 times flux loss of decaying sunspot

MMF activity( moat flow ): not caused by sunspot decay

MMF activity: linked to the continuity of the horizontal component of penumbra carrying the Evershed flow (Schlichenmaier 2002)

Real evidence of a link between MMF and penumbral field lines this work

2. Data Processing The NOAA AR 0330 was observed by SOHO MDI with a spatial and temporal sampling of 0.60” and 1 minute, respectively. From 2003 April 9 at14:05 UT to 2003 April 10 at 00:49 UT. about 10 hoursThe μ-value of NOAA AR 0330 is 0.984, which corresponds to a heliocentric angle of 10°

Fig1a Fig1b

3. RESULTS Continuum Intensity Animation

Magnetogram Animation (scaled to ±100G)

all three components found by Shine & Title (2001) can be identified: bipolar structures, unipolar structures with the same polarity as the spot, and fast-moving unipolar structures with opposite polarity. A fourth component of the MMF activity, which corresponds to an almost continuous swell of outward-moving flux that cannot be described as isolated structures but appears to be instead a large-scale process taking place everywhere in the moat.

to search for the presence of magnetic links between the penumbra and the MMF activity, The average is made in two ways: (1) using the absolute value of the individual magnetograms, giving rise to what we refer to as <lΦl>2 and (2) using the magnetograms with their true sign, producing <Φ> . The brackets refer to temporal average.

<lΦl>2<Φ>

(expanded view of Fig2)Moat filaments starting inside the penumbra

<lΦl>2 <Φ>

the mean field lines are inclined exactly 80° with respect to the vertical

moat filaments are more conspicuously seen to begin at coordinates (8, 12) as positive polarity filaments (arrows). This location corresponds to the mid-penumbra. In the left panel (absolute value of the magnetogram signal), the paths are darkened asthey reach the local penumbral neutral line and reappear afterward. They then cross the penumbral outer boundary, continue all over the moat regionThe moat filaments extend in this case for 12” beyond the penumbral boundary.

Three bipolar structures have been detected.

(1)they are all bipolar during their crossing of the moat. In contrast, the filaments in the true sign image of Figure 3 (right) areof uniform negative polarity in the moat. But remarkably, what is seen in the animations are strong bipolar structures.(2) these bipolar MMFs are generated as such inside the penumbra.

White-leading Black-leading Black-leading

4. CONCLUSIONS

(1)the moat magnetic field found in the true sign averaged image is spatially distributed in agreement with the location of the penumbral neutral line.

(2) magnetic fields in the moat region are seen to be structured in filaments that can be traced back into the mid-penumbra and that occur everywhere in the moat.(3) Bipolar MMF activity is seen to be linked to the moat filaments.(4) a link between the horizontal moat filaments, bipolar MMFs starting inside the penumbra, and the fate of the Evershed flow is established (although admittedly, we lack direct Doppler shift measurements that wouldconfirm this point). (5) The results presented in this paper actually fit rather well with current models of both Evershed flow and MMF activity.Schlichenmaier (2002) has shown that the evolution of thin flux tubes, as the Evershed-carrying flow component, can leadto density enhancements that form a serpentine component inside the penumbra.