The Evolution of Pores and the Development of Penumbrae

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Abstract
We investigate the evolution of the magnetic field in an emerging active region near disk center using data from the Advanced Stokes Polarimeter. Specifically, we follow the formation of a pore from a radiatively undisturbed region and the formation of a protospot, i.e., the appearance of a rudimentary penumbral sector for a mature pore. Our approach is to use the temporal evolution of bivariate distribution functions correlating continuum intensity, Ic, magnetic field magnitude, | |, magnetic fill fraction, f, local inclination, γ, local azimuth, , and line-of-sight Doppler velocity, vD. The highlights of our results include, (1) in the pore-forming region, a preference for the relatively strong vertical field points (1000-1500 G) to be redshifted (downflowing) and the appearance of dark pore points to be at the expense of radiatively undisturbed points; (2) an onset flux of ≈ 2 × 1019 Mx in a dark pore that appears in an area in which the flux increases by ≈ 1 × 1020 Mx prior to the pore's appearance and that previously contained an azimuth center, i.e., a magnetic concentration that otherwise has no continuum-intensity signature; (3) a threshold of (1-1.5) × 1020 Mx above which a partial penumbra forms; (4) the appearance of penumbral elements that at once having the appropriate penumbral range of field strengths, intensities, and inclination angles, i.e., no obvious gradual increase in the magnetic fields' inclination with increasing flux during the formation of penumbrae; (5) no delay between the appearance of inclined penumbral magnetic fields and the Evershed flow; and (6) a self-similarity between the pore, protospot, and a small mature sunspot with respect to the (| |, Ic), (| |, γ), (f, γ), and the (vD, Ic), (vD, γ) distributions.