Journal of Physics & Astronomy

Open Access Open Access  Restricted Access Subscription Access

3D Analytical Model of Steady Solar Faculae


Affiliations
1 Central astronomical observatory of Russian Academy of Science, S-Petersburg, Russian Federation
 

Solar facular nodes regarded as relatively stable and long-lived bright active formations with a diameter from 3 to 8 Mm and having a fine (about 1 Mm or less) magnetic filamentary structure with magnetic field strengths from 250 G to 1000 G are modeled analytically. The stationary MHD problem is solved and analytical formulae are derived that allow one to calculate the pressure, density, temperature, and Alfven Mach number in the configuration under study from the corresponding magnetic field structure. The facular node is introduced in a hydrostatic atmosphere defined by the Avrett & Loeser model and is surrounded by a weak (2G) external field corresponding to the global magnetic field intensity on the solar surface. The calculated temperature profiles of the facular node at the level of the photosphere have a characteristic shape where the temperature on the facula axis is lower than that in the surroundings but in the nearest vicinities of the axis and at the periphery of the node, the gas is 200-100 K hotter than the surroundings. Here, on the level of photosphere, the model well describes not only the central darkening of the faculae (like Wilson depression, as in sunspots), but also ring, semi-ring and segmental facular brightening observed with New Swedish 1-m Telescope at high angular resolution. In the temperature minimum region (z = 525 km), the central dip in T-profile disappears, the temperature at the facular axis considerably exceeds the temperature of the ambient plasma, and the facula as a whole is here hotter than the chromosphere. At all heights of the chromosphere the temperature of the faculae is higher than surrounding environment at the same level. This difference is particularly significant at heights of 1.5 and 2.2 Mm, where the main contribution to gas pressure within the facular node makes a pressure of the external magnetic field, which at these heights is already comparable with the internal magnetic field of the facula and even begins to surpass it. Apparently, it is these layers of the facular flux tube at heights of more than 1Mm that form the bright phenomena which are designated by observers as flocculi or plages.

Keywords

Solar Facula, Photospheric-Chromospheric Formations.
User
Notifications
Font Size

  • Аvrett EH, Loeser R. Models of the Solar Chromosphere and Transition Region from Sumer and HRTS Observations: Formation of the Extreme-Ultraviolet Spectrum of Hydrogen, Carbon and Oxygen. The Astrophy J Suppl Ser. 2008;175:229-76.

  • Baltasar H. The oscillatory behavior of solar faculae. Solar Phys. 1990;127: 289-92.

  • Berger TE, Rouppe L, Lofdahl M. Contrast analysis of solar faculae and magnetic bright points. The Astrophys J. 2007;661:1272-88.

  • Chelpanov AA, Kobanov NI, Kolobov DY. Astron Rep.2015; 59:96.

  • Kolotkov D Y, Smirnova V V, Strekalova PV, et al. Long-period quasi-periodic oscillations of a small-scale magnetic structure on the Sun, Astron Astrophys. 2017;598:4.

  • Kostik R, Khomenko E. The possible origin of facular brightness in the solar atmosphere. Astron Astrophys. 2016;589:A6.

  • Lites BW, Scharmer GB, Berger TE, et al. Three-dimensional structure of the active region photosphere as revealed by high angular resolution. Solar Phys. 2004;221:65-84.

  • Mehltretter JP. Observations of photospheric faculae at the center of the solar disk. Solar Phys. 1974;38:43-57.

  • Nakariakov VM, Aschwanden MJ, van Doorsselaere T. The possible role of vortex shedding in the excitation of kink-mode oscillations in the solar corona. Astron Astrophys. 2009;502:661-4.

  • Okunev OV, Kneer F. On the structure of polar faculae on the Sun. Astron Astrophys. 2004;425: 321-31.

  • Quintero Noda C, Suematsu Y, Cobo Ruiz B, et al. Analysis of spatially deconvolved polar faculaeMon Not R Astron Soc. 2016;460:956–65.

  • Shatten KH, Mayr HG, Omidrav K, et al. A hillock and cloud model for faculae.The Astrophys J. 1986;311:460-73.

  • Schatzman E. Model of a force free field. IAU Symp. 22, Stellar and solar magnetic fields. Amsterdam. 1965:337-345.

  • Scherrer PH, Shou J, Bush RI et al. The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO). Solar Physics. 2012;275:207-27.

  • Solov’ev AA., Kirichek EA. Analytical Model of an asymmetric sunspot with a steady plasma flow in its penumbra. Solar Physics. 2016;291:1647-63.

  • Solov’evA. A., Kirichek E.A., Magnetohydrostatics of a vertical flux tube in the solar atmosphere: coronal loops, a model of a ring flare filament. Astron Lett. 2015;41:211-24.

  • Spruit HC. Pressure equilibrium and energy balance of small photospheric flux tubes. Solar Phys. 1976;50:269-95.

  • Strekalova PV, Nagovitsyn YA, Riehokainen A, et al. Long-period variations in the magnetic field of small-scale solar structures. Geomagn Aeron. 2016;56:1052-9.

  • Thomas JH, Cram LE, Nye AH. Dynamical phenomena in sunspots. I-Observing procedures and oscillatory phenomena. II-A moving magnetic feature. Astrophys J. 1984;285:368-85.


Abstract Views: 353

PDF Views: 0




  • 3D Analytical Model of Steady Solar Faculae

Abstract Views: 353  |  PDF Views: 0

Authors

А. А. Solov'ev
Central astronomical observatory of Russian Academy of Science, S-Petersburg, Russian Federation

Abstract


Solar facular nodes regarded as relatively stable and long-lived bright active formations with a diameter from 3 to 8 Mm and having a fine (about 1 Mm or less) magnetic filamentary structure with magnetic field strengths from 250 G to 1000 G are modeled analytically. The stationary MHD problem is solved and analytical formulae are derived that allow one to calculate the pressure, density, temperature, and Alfven Mach number in the configuration under study from the corresponding magnetic field structure. The facular node is introduced in a hydrostatic atmosphere defined by the Avrett & Loeser model and is surrounded by a weak (2G) external field corresponding to the global magnetic field intensity on the solar surface. The calculated temperature profiles of the facular node at the level of the photosphere have a characteristic shape where the temperature on the facula axis is lower than that in the surroundings but in the nearest vicinities of the axis and at the periphery of the node, the gas is 200-100 K hotter than the surroundings. Here, on the level of photosphere, the model well describes not only the central darkening of the faculae (like Wilson depression, as in sunspots), but also ring, semi-ring and segmental facular brightening observed with New Swedish 1-m Telescope at high angular resolution. In the temperature minimum region (z = 525 km), the central dip in T-profile disappears, the temperature at the facular axis considerably exceeds the temperature of the ambient plasma, and the facula as a whole is here hotter than the chromosphere. At all heights of the chromosphere the temperature of the faculae is higher than surrounding environment at the same level. This difference is particularly significant at heights of 1.5 and 2.2 Mm, where the main contribution to gas pressure within the facular node makes a pressure of the external magnetic field, which at these heights is already comparable with the internal magnetic field of the facula and even begins to surpass it. Apparently, it is these layers of the facular flux tube at heights of more than 1Mm that form the bright phenomena which are designated by observers as flocculi or plages.

Keywords


Solar Facula, Photospheric-Chromospheric Formations.

References