Bibcode
Keppens, R.; Martinez Pillet, V.
Bibliographical reference
Astronomy and Astrophysics, v.316, p.229-242
Advertised on:
12
1996
Journal
Citations
120
Refereed citations
107
Description
We investigate the radial variation of the magnetic field structure
across sunspots, pores and azimuth centers (ACs). We define ACs as
magnetic structures of about the same size as pores (all structures
studied here are larger than 3 Mm diameter), but without a clear (at
least 5%) continuum decrease associated with them. We start from the
full 3D vector fields as observed with the Advanced Stokes Polarimeter
(ASP), and perform a statistical study of the azimuthally averaged field
components in the local cylindrical reference frame centered on the
structures. Our statistical study comprises a sample of 16 sunspot
observations, a sample of 51 pores, and a sample of 22 ACs. For all
structures, we derive mean radial profiles and their standard
deviations. Due to the relatively large sample of pores, we are able to
investigate variations of this mean radial field structure with the size
of the pores. On the basis of our statistics, we identify systematic
changes in the magnetic field structure over a considerable size range.
We suggest how this may be the natural consequence of a formation
scenario for the largest pores, by a lateral clustering of magnetic
elements. Indeed, in this process, an AC may develop into a dark pore
and gradually grow in size through the incremental addition of magnetic
flux. Several observations where ACs turn into pores provide an estimate
of about 4-5x10^19^Mx for the critical magnetic flux at which such
transitions occur. We confirm the existence of a magnetic canopy for
pores of all sizes, as their magnetic extent is virtually always larger
than the associated continuum darkening. We observe a relatively rapid
change in the continuum appearance of a large pore in the sample. We
identify the associated changes in the field structure, and confront it
with the determined mean field variation across sunspots. It appears
that we have witnessed the formation of a partial penumbra.