The effects of numerical resolution, heating timescales and background heating on thermal non-equilibrium in coronal loops

Abstract

Thermal non-equilibrium (TNE) is believed to be a potentially important process in understanding some properties of the magnetically closed solar corona. Through one-dimensional hydrodynamic models, this paper addresses the importance of the numerical spatial resolution, footpoint heating timescales and background heating on TNE. Inadequate transition region (TR) resolution can lead to significant discrepancies in TNE cycle behaviour, with TNE being suppressed in under-resolved loops. A convergence on the periodicity and plasma properties associated with TNE required spatial resolutions of less than 2 km for a loop of length 180 Mm. These numerical problems can be resolved using an approximate method that models the TR as a discontinuity using a jump condition, as proposed by Johnston et al. (2017a,b). The resolution requirements (and so computational cost) are greatly reduced while retaining good agreement with fully resolved results. Using this approximate method we (i) identify different regimes for the response of coronal loops to time-dependent footpoint heating including one where TNE does not arise and (ii) demonstrate that TNE in a loop with footpoint heating is suppressed unless the background heating is sufficiently small. The implications for the generality of TNE are discussed.

15 pages, 10 figures, 1 table, accepted for publication in A&A

References in corpus (11)

• Highly Efficient Modeling of Dynamic Coronal Loops
• Key Aspects of Coronal Heating
• Evidence of Non-Thermal Particles in Coronal Loops Heated Impulsively by Nanoflares
• The multi-thermal and multi-stranded nature of coronal rain
• The Role of Type II Spicules in the Upper Solar Atmosphere
• Coronal rain in magnetic arcades: Rebound shocks, Limit cycles, and Shear flows
• Long-Period Intensity Pulsations in Coronal Loops Explained by Thermal Non-Equilibrium Cycles
• Continuous upflows and sporadic downflows observed in active regions
• Coronal rain in magnetic bipolar weak fields
• Inference of Heating Properties from "Hot" Non-flaring Plasmas in Active Region Cores. II. Nanoflare Trains
• A new approach for modelling chromospheric evaporation in response to enhanced coronal heating: II Non-uniform heating

Cited by in corpus (4)

• Multi-scale observations of thermal non-equilibrium cycles in coronal loops
• Electron Beams Cannot Directly Produce Coronal Rain
• Self-consistent 3D radiative MHD simulations of coronal rain formation and evolution
• On the spectroscopic detection of periodic plasma flows in loops undergoing thermal non-equilibrium