The Evolution of Pores and the Development of Penumbrae

Abstract

We investigate the evolution of the magnetic Ðeld in an emerging active region near disk center using data from the Advanced Stokes Polarimeter. SpeciÐcally, we follow the formation of a pore from a radi-atively undisturbed region and the formation of a protospot, i.e., the appearance of a rudimentary pen-umbral sector for a mature pore. Our approach is to use the temporal evolution of bivariate distribution functions correlating continuum intensity, magnetic Ðeld magnitude, o B o, magnetic Ðll fraction, f, local I c , inclination, c, local azimuth, /, and line-of-sight Doppler velocity, The highlights of our results v D. include, (1) in the pore-forming region, a preference for the relatively strong vertical Ðeld points (1000È 1500 G) to be redshifted (downÑowing) and the appearance of dark pore points to be at the expense of radiatively undisturbed points ; (2) an onset Ñux of B2 ] 1019 Mx in a dark pore that appears in an area in which the Ñux increases by B1 ] 1020 Mx prior to the poreÏs appearance and that previously contained an azimuth center, i.e., a magnetic concentration that otherwise has no continuum-intensity signature ; (3) a threshold of (1È1.5) ] 1020 Mx above which a partial penumbra forms ; (4) the appearance of penumbral elements that at once having the appropriate penumbral range of Ðeld strengths, intensities, and inclination angles, i.e., no obvious gradual increase in the magnetic ÐeldsÏ inclination with increasing Ñux during the formation of penumbrae ; (5) no delay between the appearance of inclined penumbral magnetic Ðelds and the Evershed Ñow ; and (6) a self-similarity between the pore, protospot, and a small mature sunspot with respect to the (o B o, (oBo, c), (f, c), and the distributions.