Damping of slow magnetoacoustic oscillations by the misbalance between heating and cooling processes in the solar corona
Published: 08/2019
Left: parametric regions of the wave damping enhancement (I), suppression (II), and thermal over-stability (III). Grey-shaded regions indicate the values of τ1,2 where the q-factor is in between 1 (the green line) and 2 (the blue line, Ia), and in between 2 and 3 (the purple line, Ib). The red, green, and blue symbols indicate some arbitrary values of τ1,2 chosen for the numerical solutions shown. Right: heating/cooling times τ1,2 determined for the CHIANTI radiative cooling, and the heating function in the form H(ρ, T) ∝ ρ^aT^b for the varying temperature and density power indices a and b. The grey-shaded areas indicate the values of a and b where 1 < q-factor < 2 (light grey) and 2 < q-factor < 3 (dark grey). The green, blue, and purple lines show q-factor equals 1, 2, and 3, respectively.
Astronomy & Astrophysics, Volume 628, id.A133, 6 pp.
Kolotkov D. Y., Nakariakov V. M., Zavershinskii D. I.
Context. Rapidly decaying slow magnetoacoustic waves are regularly observed in the solar coronal structures, offering a promising tool for a seismological diagnostics of the coronal plasma, including its thermodynamical properties.
Aims: The effect of damping of standing slow magnetoacoustic oscillations in the solar coronal loops is investigated accounting for field-aligned thermal conductivity and a wave-induced misbalance between radiative cooling and some unspecified heating rates.
Methods: The non-adiabatic terms were allowed to be arbitrarily large, corresponding to the observed values. The thermal conductivity was taken in its classical form, and a power-law dependence of the heating function on the density and temperature was assumed. The analysis was conducted in the linear regime and in the infinite magnetic field approximation.
Results: The wave dynamics is found to be highly sensitive to the characteristic timescales of the thermal misbalance. Depending on certain values of the misbalance, timescales three regimes of the wave evolution were identified, namely the regime of a suppressed damping, enhanced damping in which the damping rate drops down to observational values, and acoustic over-stability. The specific regime is determined by the dependences of the radiative cooling and heating functions on thermodynamical parameters of the plasma in the vicinity of the perturbed thermal equilibrium.
Conclusions: The comparison of the observed and theoretically derived decay times and oscillation periods allows us to constrain the coronal heating function. For typical coronal parameters, the observed properties of standing slow magnetoacoustic oscillations could be readily reproduced with a reasonable choice of the heating function.
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