Properties of multistranded, impulsively heated hydrodynamic loop models

Abstract

Aims. We investigate the capability of multistranded loop models subject to nanoflare heating to reproduce the properties recently observed in coronal loops at extreme ultraviolet (EUV) wavelengths. Methods. One-dimensional hydrodynamic simulations of magnetic loop strands were performed with an impulsive, footpointlocalised heating, with a moderate asymmetry between the two loop halves that was produced either by a sequence of identical nanoflares with a given cadence time t C or by a single energy pulse. The temporal evolution of the emission of a multistranded loop was modelled by simply combining the results of independent single-strand simulations, neglecting any spatial interaction among the strands, and was compared with TRACE and SDO/AIA light curves. The density excess with respect to hydrostatic equilibrium (the ψ factor) was evaluated with the filter-ratio technique. Results. Both loop models exhibit a density excess compared with hydrostatic equilibrium models, which agrees well with the observed values (1 ψ 12). However, in the single-pulse model the light curve and density excess maxima do not match. On the other hand, the models with a sequence of nanoflares predict strong emission at lower temperatures that cannot be reconciled with the available observations.

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

“…The rapid cooling is driven locally by the thermal instability and leads to the formation of the condensation at the loop apex, as found by others (e.g. Müller et al 2003Müller et al , 2004Müller et al , 2005Mok et al 2008;Antolin et al 2010;Susino et al 2010;Lionello et al 2013a;Mikić et al 2013;Susino et al 2013;Mok et al 2016;Froment et al 2018). The condensation has a peak density of around 14 × 10 15 m −3 at 195 minutes but then quickly falls down the right-hand leg of the loop.…”

“…While models of TNE predict generic global and local features in spectral diagnostics of the solar corona including loops undergoing a cyclic heating and cooling evolution of evaporation and condensation, the existence of these cycles depends on several parameters (e.g. Antiochos et al 2000;Karpen et al 2001;Müller et al 2003Müller et al , 2004Müller et al , 2005Mendoza-Briceño et al 2005;Mok et al 2008;Antolin et al 2010;Susino et al 2010;Lionello et al 2013a;Mikić et al 2013;Susino et al 2013;Mok et al 2016) which include (but need not be limited to) geometrical factors (such as the loop length and area expansion) and the nature of the heating mechanism (its spatial and temporal distribution, the degree of asymmetry between both footpoints, its stochasticity and so on). As shown by Froment et al (2018) the existence of TNE cycles seem to be very sensitive to some of these parameters, suggesting that if they are approximately uniformly distributed, the vast majority of loops should not exhibit TNE.…”

“…TNE is a phenomenon that can occur in coronal loops when the heating is concentrated towards the footpoints (e.g. Antiochos et al 2000;Karpen et al 2001;Müller et al 2003Müller et al , 2004Müller et al , 2005Mendoza-Briceño et al 2005;Mok et al 2008;Antolin et al 2010;Susino et al 2010;Lionello et al 2013a;Mikić et al 2013;Susino et al 2013;Mok et al 2016). This localised energy deposition drives evaporative upflows that fill the loop with hot dense plasma, increasing the coronal density and radiative losses.…”

Multi-Stranded Coronal Loops: Quantifying Strand Number and Heating Frequency from Simulated Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) Observations

“…Their results support a scenario whereby long loops formed of multiple strands undergo periodic heating and cooling. Similarly, Susino et al (2013) demonstrate that whilst 1D multi-stranded models can predict observed values derived from TRACE and AIA filter ratios, they cannot explain all of the characteristics of warm overdense loops as such models assume spatial interactions between individual strands can be neglected, which may not always be the case (Hood et al, 2016;Reid et al, 2018Reid et al, , 2020.…”

Multi-Stranded Coronal Loops: Quantifying Strand Number and Heating Frequency from Simulated Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) Observations

“…Their results support a scenario whereby long loops formed of multiple strands undergo periodic heating and cooling. Similarly, Susino et al (2013) demonstrate that whilst 1D multi-stranded models can predict observed values derived from TRACE and AIA filter ratios, they cannot explain all of the characteristics of warm over-dense loops as such models assume spatial interactions between individual strands can be neglected, which may not always be the case (Hood et al, 2016;Reid et al, 2018Reid et al, , 2020.…”