The Effect of the Chromospheric Temperature on Coronal Heating

Abstract

Recent observational and numerical studies show a variety of thermal structures in the solar chromosphere. Given that the thermal interplay across the transition region is a key to coronal heating, it is worth investigating how different thermal structures of the chromosphere yield different coronal properties. In this work, by MHD simulations of Alfvén-wave heating of coronal loops, we study how the coronal properties are affected by the chromospheric temperature. To this end, instead of solving the radiative transfer equation, we employ a simple radiative loss function so that the chromospheric temperature is easily tuned. When the chromosphere is hotter, because the chromosphere extends to a larger height, the coronal part of the magnetic loop becomes shorter, which enhances the conductive cooling. A larger loop length is therefore required to maintain the high-temperature corona against the thermal conduction. From our numerical simulations we derive a condition for the coronal formation with respect to the half loop length l loop in a simple form: l loop > aT min + l th , where T min is the minimum temperature in the atmosphere, and parameters a and l th have negative dependencies on the coronal field strength. Our conclusion is that the chromospheric temperature has a nonnegligible impact on coronal heating for loops with small lengths and weak coronal fields. In particular, the enhanced chromospheric heating could prevent the formation of the corona.

Coronal Loops with Different Metallicities and Generalized RTV Scaling Laws

“…Due to the simple form, Equation (A1) has been widely used in numerical simulations that treat from the photosphere and the chromosphere to the corona (Moriyasu et al 2004;Suzuki & Inutsuka 2005;Matsumoto & Shibata 2010;Suzuki 2018;Washinoue & Suzuki 2019). However, it should be noted that it is required to set a cutoff temperature of radiative cooling to avoid the extremely low chromospheric temperatures (Washinoue et al 2022).…”

“…In this study, we consider a loop as a one-dimensional semicircular magnetic flux tube anchored in the photosphere, where we adopt the same configuration in Washinoue et al (2022). The expansion factor f (s) is given at each position to define a loop geometry.…”

“…We solve the one-dimensional MHD equations with radiative cooling, thermal conduction, and phenomenological turbulent dissipation (see Section 2.3 in Washinoue et al 2022).…”

“…One should be careful to model the radiative loss in the chromosphere because the physical condition of the chromosphere is directly connected to the Alfvén wave propagation and the coronal heating (Washinoue et al 2022). Therefore, it is worthwhile to examine how the atmospheric profiles are affected by different models for the chromosphere.…”

Effect of Magnetic Diffusion in the Chromosphere on the Solar Wind

“…Following Shoda et al (2018a; see also Shimizu et al 2022;Washinoue et al 2022), we consider the dissipation of Alfvénic waves via turbulence in a phenomenological way (Hossain et al 1995;Cranmer et al 2007). D v i ^and D b i ^in Equations (5) and (7) denote turbulent dissipation coefficients of velocity and magnetic field amplitudes:…”