RADIATIVE HYDRODYNAMIC SIMULATIONS OF ACOUSTIC WAVES IN SUNSPOTS

Journal Article · Sun Oct 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/1/888· OSTI ID:21464673

Bard, S ^[1]; Carlsson, M ^[2]

---

1. Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo (Norway)
2. Also at Center of Mathematics for Applications, University of Oslo, P.O. Box 1053, Blindern, N-0316 Oslo, Norway. (Norway)

We investigate the formation and evolution of the Ca II H line in a sunspot. The aim of our study is to establish the mechanisms underlying the formation of the frequently observed brightenings of small regions of sunspot umbrae known as 'umbral flashes'. We perform fully consistent NLTE radiation hydrodynamic simulations of the propagation of acoustic waves in sunspot umbrae and conclude that umbral flashes result from increased emission of the local solar material during the passage of acoustic waves originating in the photosphere and steepening to shock in the chromosphere. To quantify the significance of possible physical mechanisms that contribute to the formation of umbral flashes, we perform a set of simulations on a grid formed by different wave power spectra, different inbound coronal radiation, and different parameterized chromospheric heating. Our simulations show that the waves with frequencies in the range 4.5-7.0 mHz are critical to the formation of the observed blueshifts of umbral flashes while waves with frequencies below 4.5 mHz do not play a role despite their dominance in the photosphere. The observed emission in the Ca II H core between flashes only occurs in the simulations that include significant inbound coronal radiation and/or extra non-radiative chromospheric heating in addition to shock dissipation.

• OSTI ID: 21464673
• Journal Information: Astrophysical Journal, Vol. 722, Issue 1; Other Information: DOI: 10.1088/0004-637X/722/1/888; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CHROMOSPHERE
OSCILLATIONS
PHOTOSPHERE
SIMULATION
SOLAR SYSTEM EVOLUTION
SOUND WAVES
SUN
SUNSPOTS
WAVE POWER
ATMOSPHERES
ENERGY SOURCES
EVOLUTION
MAIN SEQUENCE STARS
POWER
RENEWABLE ENERGY SOURCES
SOLAR ACTIVITY
SOLAR ATMOSPHERE
STARS
STARSPOTS
STELLAR ACTIVITY
STELLAR ATMOSPHERES