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Title: Emergence of granular-sized magnetic bubbles through the solar atmosphere. I. Spectropolarimetric observations and simulations

Abstract

We study a granular-sized magnetic flux emergence event that occurred in NOAA 11024 in 2009 July. The observations were made with the CRISP spectropolarimeter at the Swedish 1 m Solar Telescope achieving a spatial resolution of 0.''14. Simultaneous full Stokes observations of the two photospheric Fe I lines at 630.2 nm and the chromospheric Ca II 854.2 nm line allow us to describe in detail the emergence process across the solar atmosphere. We report here on three-dimensional (3D) semi-spherical bubble events, where instead of simple magnetic footpoints, we observe complex semi-circular feet straddling a few granules. Several phenomena occur simultaneously, namely, abnormal granulation, separation of opposite-polarity legs, and brightenings at chromospheric heights. However, the most characteristic signature in these events is the observation of a dark bubble in filtergrams taken in the wings of the Ca II 854.2 nm line. There is a clear coincidence between the emergence of horizontal magnetic field patches and the formation of the dark bubble. We can infer how the bubble rises through the solar atmosphere as we see it progressing from the wings to the core of Ca II 854.2 nm. In the photosphere, the magnetic bubble shows mean upward Doppler velocities of 2more » km s{sup –1} and expands at a horizontal speed of 4 km s{sup –1}. In about 3.5 minutes it travels some 1100 km to reach the mid chromosphere, implying an average ascent speed of 5.2 km s{sup –1}. The maximum separation attained by the magnetic legs is 6.''6. From an inversion of the observed Stokes spectra with the SIR code, we find maximum photospheric field strengths of 480 G and inclinations of nearly 90° in the magnetic bubble interior, along with temperature deficits of up to 250 K at log τ = –2 and above. To aid the interpretation of the observations, we carry out 3D numerical simulations of the evolution of a horizontal, untwisted magnetic flux sheet injected in the convection zone, using the Bifrost code. The computational domain spans from the upper convection zone to the lower corona. In the modeled chromosphere, the rising flux sheet produces a large, cool, magnetized bubble. We compare this bubble with the observed ones and find excellent agreement, including similar field strengths and velocity signals in the photosphere and chromosphere, temperature deficits, ascent speeds, expansion velocities, and lifetimes.« less

Authors:
; ;  [1];  [2]
  1. Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo (Norway)
  2. Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3040, E-18080 Granada (Spain)
Publication Date:
OSTI Identifier:
22348087
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 781; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CHROMOSPHERE; COMPUTERIZED SIMULATION; EVOLUTION; EXPANSION; GRANULATION; LIFETIME; MAGNETIC FIELDS; MAGNETIC FLUX; PHOTOSPHERE; SPATIAL RESOLUTION; SPECTRA; SPHERICAL CONFIGURATION; SUN; TELESCOPES; THREE-DIMENSIONAL CALCULATIONS; VELOCITY

Citation Formats

Ortiz, Ada, Hansteen, Viggo H., Van der Voort, Luc Rouppe, Bellot Rubio, Luis R., and De la Cruz Rodríguez, Jaime, E-mail: ada@astro.uio.no. Emergence of granular-sized magnetic bubbles through the solar atmosphere. I. Spectropolarimetric observations and simulations. United States: N. p., 2014. Web. doi:10.1088/0004-637X/781/2/126.
Ortiz, Ada, Hansteen, Viggo H., Van der Voort, Luc Rouppe, Bellot Rubio, Luis R., & De la Cruz Rodríguez, Jaime, E-mail: ada@astro.uio.no. Emergence of granular-sized magnetic bubbles through the solar atmosphere. I. Spectropolarimetric observations and simulations. United States. https://doi.org/10.1088/0004-637X/781/2/126
Ortiz, Ada, Hansteen, Viggo H., Van der Voort, Luc Rouppe, Bellot Rubio, Luis R., and De la Cruz Rodríguez, Jaime, E-mail: ada@astro.uio.no. 2014. "Emergence of granular-sized magnetic bubbles through the solar atmosphere. I. Spectropolarimetric observations and simulations". United States. https://doi.org/10.1088/0004-637X/781/2/126.
@article{osti_22348087,
title = {Emergence of granular-sized magnetic bubbles through the solar atmosphere. I. Spectropolarimetric observations and simulations},
author = {Ortiz, Ada and Hansteen, Viggo H. and Van der Voort, Luc Rouppe and Bellot Rubio, Luis R. and De la Cruz Rodríguez, Jaime, E-mail: ada@astro.uio.no},
abstractNote = {We study a granular-sized magnetic flux emergence event that occurred in NOAA 11024 in 2009 July. The observations were made with the CRISP spectropolarimeter at the Swedish 1 m Solar Telescope achieving a spatial resolution of 0.''14. Simultaneous full Stokes observations of the two photospheric Fe I lines at 630.2 nm and the chromospheric Ca II 854.2 nm line allow us to describe in detail the emergence process across the solar atmosphere. We report here on three-dimensional (3D) semi-spherical bubble events, where instead of simple magnetic footpoints, we observe complex semi-circular feet straddling a few granules. Several phenomena occur simultaneously, namely, abnormal granulation, separation of opposite-polarity legs, and brightenings at chromospheric heights. However, the most characteristic signature in these events is the observation of a dark bubble in filtergrams taken in the wings of the Ca II 854.2 nm line. There is a clear coincidence between the emergence of horizontal magnetic field patches and the formation of the dark bubble. We can infer how the bubble rises through the solar atmosphere as we see it progressing from the wings to the core of Ca II 854.2 nm. In the photosphere, the magnetic bubble shows mean upward Doppler velocities of 2 km s{sup –1} and expands at a horizontal speed of 4 km s{sup –1}. In about 3.5 minutes it travels some 1100 km to reach the mid chromosphere, implying an average ascent speed of 5.2 km s{sup –1}. The maximum separation attained by the magnetic legs is 6.''6. From an inversion of the observed Stokes spectra with the SIR code, we find maximum photospheric field strengths of 480 G and inclinations of nearly 90° in the magnetic bubble interior, along with temperature deficits of up to 250 K at log τ = –2 and above. To aid the interpretation of the observations, we carry out 3D numerical simulations of the evolution of a horizontal, untwisted magnetic flux sheet injected in the convection zone, using the Bifrost code. The computational domain spans from the upper convection zone to the lower corona. In the modeled chromosphere, the rising flux sheet produces a large, cool, magnetized bubble. We compare this bubble with the observed ones and find excellent agreement, including similar field strengths and velocity signals in the photosphere and chromosphere, temperature deficits, ascent speeds, expansion velocities, and lifetimes.},
doi = {10.1088/0004-637X/781/2/126},
url = {https://www.osti.gov/biblio/22348087}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 781,
place = {United States},
year = {Sat Feb 01 00:00:00 EST 2014},
month = {Sat Feb 01 00:00:00 EST 2014}
}