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Depth-dependent global properties of a sunspot observed by Hinode (SOT/SP) View all abstracts by submitter

Sanjiv Tiwari   Submitted: 2015-08-26 13:32

The three dimensional structure of sunspots has been extensively studied for the last two decades. A recent advancement of the Stokes inversion technique prompts us to revisit the problem. In the present work, we aim to investigate the global depth-dependent thermal, velocity and magnetic properties of a sunspot, as well as the interconnection between various local properties. High quality Stokes profiles of the disk centered, regular, leading sunspot of NOAA AR 10933 acquired by the Solar Optical Telescope/Spectropolarimeter onboard the Hinode spacecraft are analyzed. To obtain the depth-dependent stratification of the physical parameters, we have utilized the recently developed spatially coupled version of the SPINOR inversion code. We first study the azimuthally averaged physical parameters of the sunspot. The vertical temperature gradient in the lower to mid-photosphere is smallest in the umbra, it is considerably larger in the penumbra and still somewhat larger in the spot's surroundings. The azimuthally averaged field becomes more horizontal with radial distance from the center of the spot, but more vertical with height. At continuum optical depth unity, the line-of-sight velocity shows an average upflow of ~ 300 ms-1 in the inner penumbra and an average downflow of ~ 1300 ms-1 in the outer penumbra. The downflow continues outside the visible penumbral boundary. The sunspot shows at most a moderate negative twist of < 5° at log(τ) = 0, which increases with height. The sunspot umbra and the spines of the penumbra show considerable similarity in their physical properties albeit with some quantitative differences (weaker, somewhat more horizontal fields in spines, commensurate with their location further away from the sunspot's core). The temperature shows a general anticorrelation with the field strength, with the exception of the heads of penumbral filaments, where a weak positive correlation is found. The dependence of the physical parameters on each other over the full sunspot shows a qualitative similarity to that of a standard penumbral filament and its surrounding spines. The large-scale variation of the physical parameters of a sunspot at various optical depths is presented. Our results suggest that the spines in the penumbra are basically the outward extension of the umbra. The spines and the penumbral filaments are together the basic elements forming a sunspot penumbra.

Authors: Tiwari, Sanjiv K.; van Noort, Michiel; Solanki, Sami K.; Lagg, Andreas
Projects: Hinode/SOT

Publication Status: A&A, accepted
Last Modified: 2015-08-27 10:27
Go to main E-Print page  Magnetic Flux and Helicity of Magnetic Clouds  The Formation and Magnetic Structures of Active-region Filaments Observed by NVST, SDO, and Hinode  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

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