Three-Dimensional Structure of the Active Region Photosphere as Revealed by High Angular Resolution B. W. Lites et al. 2004, Sol. Phys., 221, 65 Solar Seminar: Okamoto

Abstract ・ blue continuum images of active regions at ~60° ・ the new Swedish 1-m Solar Telescope (SST) ・ light bridges are raised above the dark surroundings ・ facular brightenings occur on the disk-center side of the granules ・・・ ・ these newly observational aspects of photospheric magnetic fields shoud provide constraints for MHD models

Introduction 3-D magnetic-field structures are apparent  valuable diagnostic for topology of the magnetic field Owing to the very small scale height of the photosphere  the magnetic structuring of the photospheric “surface” is not readily apparent The small scale structure of the magnetized solar atmosphere is controlled by a complex interplay of magnetism, gravity, radiation, and thermodynamics. The main thrust of this work is to present structures with unprecedented resolution.

Observation ・ the new Swedish 1-m Telescope (SST) on La Palma, Canary Islands ・ S15 E53 (NOAA on 24 July 2002, 12:27 UT) ・ S07 W55 (NOAA on 25 July 2002, 13:38 UT) ・ 4877 Å ・ 2010 x 2029 pix / 0.12” ・ prototype AO

Analysis (1. Light bridge) Light bridges bounded by ・ very narrow dark lines oriented perpendicular to the axis of the bridge ・ a dark line running parallel to the axis of the bridge

Berger and Berdyugina (2003) : grains, overturning magneto-convection  must be clarified with the aid of spectroscopy and spectro-polarimetry at very high angular resolution The light bridges that extend into penumbrae do not have distinct grains or dark lanes; resemble the fine structure of the penumbra.  the key : measurements of flows and fields at very high angular resolution Analysis (1. Light bridge)

The dark lane is the high point of a ridge elevated above the dark umbral floor.  the estimates of the height range: 200~350 km; mean: 300 km

Analysis (1. Light bridge) All dark umbral floors appear to be depressions below the brighter features. The structures of light bridges are larger than in the centers of the large umbrae; 200~450 km; mean: 300 km

Analysis (1. Light bridge) The raised structures become obvious when the resolution is high. Images with degraded resolution are shown. (0.2” and 0.3”) The increase of opacity with increasing temperature can explain much of the height differential of the light bridge structures. light bridges: manifestation of the magneto-convective processes that govern the evolution of sunspots at the photosphere

Analysis (2. Facular elements) Faculae: continuum brightness enhancement of magnetic elements viewed near the limb The facular brightenings occur on the disk center side of granules. non-magnetic granulation magnetic granulation

to explain the extended brightening ・ the plage fields fan out  expose more of the wall and floor of the flux tube to explain brightening ・ temperature enhancements above the plage (~200K) Key: a time series of images at this angular resolution Analysis (2. Facular elements) spatial extent of facular brightening (larger than the typical size (<0.25”) of the filigree in continuum near the disk center)  harboring the strong magnetic fields (extending >0.5”)

dark boundary spacing the facular brightening: the widths approach the resolution (non-magnetic granulation regions show much less distinct intergranular lanes) Analysis (2. Facular elements) (a manifestation of the convective dynamics in the vicinity of the flux tubes) the combination of - the depression of τ=1 surface due to magnetic pressure - the thermal depression of the intergranular lanes due to reduced opacity in non-magnetic granulation - the resulting curvature of the cooler optical surface near the flux tube  produce a local effect akin to limb darkening

Summary ・ blue comtinuum images of active regions at ~60° -- light bridges are raised above the dark surroundings -- facular brightenings occur on the disk-center side of the granules  measurements of flows and fields at very high angular resolution ・ these newly observational aspects of photospheric magnetic fields shoud provide constraints for MHD models Solar-B/SOT: (NFI: Narrowband Filter Imager) Fe I (5250 Å ), Fe I (5576 Å ), Fe I (6302 Å ) ： photosphere Mg I (5172 Å ), Na I (5896 Å ), Hα (6563 Å ) ： chromosphere