Characterization of magneto-convection in sunspots The Gough-Tayler stability criterion in MURaM sunspot simulations

0552640 - ASÚ 2022 RIV FR eng J - Článek v odborném periodiku
Schmassmann, M. - Rempel, M. - Bello González, N. - Schlichenmaier, R. - Jurčák, Jan
Characterization of magneto-convection in sunspots The Gough-Tayler stability criterion in MURaM sunspot simulations.
Astronomy & Astrophysics. Roč. 656, December (2021), č. článku A92. ISSN 0004-6361. E-ISSN 1432-0746
Institucionální podpora: RVO:67985815
Klíčová slova: Sun * sunspots * magnetic fields
Obor OECD: Astronomy (including astrophysics,space science)
Impakt faktor: 6.240, rok: 2021
Způsob publikování: Open access s časovým embargem
https://doi.org/10.1051/0004-6361/202141607

We analyse a sunspot simulation in an effort to understand the origin of the convective instabilities giving rise to the penumbral and umbral distinct regimes. We applied the criterion from Gough & Tayler (1966, MNRAS, 133, 85), accounting for the stabilising effect of the vertical magnetic field, to investigate the convective instabilities in a MURaM sunspot simulation. We find: (1) a highly unstable shallow layer right beneath the surface extending all over the simulation box in which convection is triggered by radiative cooling in the photosphere, (2) a deep umbral core (beneath -5 Mm) stabilised against overturning convection that underlies a region with stable background values permeated by slender instabilities coupled to umbral dots, (3) filamentary instabilities below the penumbra nearly parallel to the surface and undulating instabilities coupled to the penumbra which originate in the deep layers. These deep-rooted instabilities result in the vigorous magneto-convection regime characteristic of the penumbra, (4) convective downdrafts in the granulation, penumbra, and umbra develop at about 2 km s(-1), 1 km s(-1), and 0.1 km s(-1), respectively, indicating that the granular regime of convection is more vigorous than the penumbra convection regime, which, in turn, is more vigorous than the close-to-steady umbra, (5) the GT criterion outlines both the sunspot magnetopause and peripatopause, highlighting the tripartite nature of the sub-photospheric layers of magnetohydrodynamic (MHD) sunspot models, and, finally, (6) the Jurcak criterion is the photospheric counterpart of the GT criterion in deep layers. The GT criterion as a diagnostic tool reveals the tripartite nature of sunspot structure with distinct regimes of magneto-convection in the umbra, penumbra, and granulation operating in realistic MHD simulations.
Trvalý link: http://hdl.handle.net/11104/0327756