Computer Science – Numerical Analysis
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...433..811r&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 433, no. 2, p. 811-818
Computer Science
Numerical Analysis
11
Atmospheric Pressure, Conductive Heat Transfer, Perturbation, Plasma Cooling, Stellar Atmospheres, Stellar Temperature, Thermal Stability, Abundance, Computerized Simulation, Hydrodynamic Equations, Magnetohydrodynamic Flow, Numerical Analysis, Optical Thickness
Scientific paper
We investigate the thermal stability of isobaric perturbations in a stratified isothermal background atmosphere with solar abundances, as resulting from the competition of optically thin plasma radiative cooling and of heating conducted from the surrounding atmosphere. We have analyzed the threshold line between stable and unstable perturbations, in the plane of the two important control parameters: the initial size of the perturbation and the temperature of the unperturbed medium; this line changes with the pressure of the unperturbed atmosphere. We have extended the results of linear perturbation analysis by means of numerical calculations of the evolution of spherical isobaric perturbations, using a two-dimensional hydrodynamic code including Spitzer heat conduction. We explore a wide range of the parameters appropriate to the solar and stellar upper atmospheres: the background uniform temperature is between 105 K and 107 K, the initial pressure betweeen 0.1 and 10 dyn/sq cm, and the perturbation size between 105 and 1010 cm. The numerical results are in substantial agreement with the linear analysis. We discuss possible implications of our results also in terms of observable effects, especially concerning plasma downflows, and propose thermal instability as a possible candidate to explain the observed redshifts in solar and stellar transition region lines.
Peres Giovanni
Reale Fabio
Serio Salvatore
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