Dear all,
We recently published a paper that modifies the Enthalpy-Based Thermal Evolution of Loop (EBTEL) model by relaxing the assumption of subsonic flows. We also discuss a simple criterion to predict if Mach numbers produced by 0D simulations are reliable.
The paper can be accessed at https://iopscience.iop.org/article/10.3847/1538-4357/ac3009 or alternatively on arxiv at https://arxiv.org/abs/2110.03204. The code is available at https://github.com/rice-solar-physics/EBTEL3
The abstract of the work is given below:
Plasma-filled loop structures are common in the solar corona. Because detailed modeling of the dynamical evolution of these structures is computationally costly, an efficient method for computing approximate but quick physics-based solutions is to rely on space-integrated 0D simulations. The enthalpy-based thermal evolution of loops (EBTEL) framework is a commonly used method to study the exchange of mass and energy between the corona and transition region. EBTEL solves for density, temperature, and pressure, averaged over the coronal part of the loop, the velocity at the coronal base, and the instantaneous differential emission measure distribution in the transition region. The current single-fluid version of the code, EBTEL2, assumes that at all stages the flows are subsonic. However, sometimes the solutions show the presence of supersonic flows during the impulsive phase of heat input. It is thus necessary to account for this effect. Here, we upgrade EBTEL2 to EBTEL3 by including the kinetic energy term in the Navier–Stokes equation. We compare the solutions from EBTEL3 with those obtained using EBTEL2, as well as the state-of-the-art field-aligned hydrodynamics code HYDRAD. We find that the match in pressure between EBTEL3 and HYDRAD is better than that between EBTEL2 and HYDRAD. Additionally, the velocities predicted by EBTEL3 are in close agreement with those obtained with HYDRAD when the flows are subsonic. However, EBTEL3 solutions deviate substantially from HYDRAD's when the latter predicts supersonic flows. Using the mismatches in the solution, we propose a criterion to determine the conditions under which EBTEL can be used to study flows in the system.
I will be happy to get your valuable feedback.
Kind Regards, Abhishek Rajhans
loops@solar.physics.montana.edu