Browsing by Author "Klimchuk, James A."

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    Flows in Enthalpy-based Thermal Evolution of Loops
    (IOP Publishing, 2022) Rajhans, Abhishek; Tripathi, Durgesh; Bradshaw, Stephen J.; Kashyap, Vinay L.; Klimchuk, James A.
    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 (EB℡) framework is a commonly used method to study the exchange of mass and energy between the corona and transition region. EB℡ solves for density, temperature, and pressure, averaged over the coronal part of the loop, velocity at coronal base, and the instantaneous differential emission measure distribution in the transition region. The current single-fluid version of the code, EB℡2, 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 EB℡2 to EB℡3 by including the kinetic energy term in the Navier–Stokes equation. We compare the solutions from EB℡3 with those obtained using EB℡2, as well as the state-of-the-art field-aligned hydrodynamics code HYDRAD. We find that the match in pressure between EB℡3 and HYDRAD is better than that between EB℡2 and HYDRAD. Additionally, the velocities predicted by EB℡3 are in close agreement with those obtained with HYDRAD when the flows are subsonic. However, EB℡3 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 EB℡ can be used to study flows in the system.
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    Hard X-Ray Constraints on Small-scale Coronal Heating Events
    (IOP Publishing, 2018) Marsh, Andrew J.; Smith, David M.; Glesener, Lindsay; Klimchuk, James A.; Bradshaw, Stephen J.; Vievering, Juliana; Hannah, Iain G.; Christe, Steven; Ishikawa, Shin-nosuke; Krucker, Säm
    Much evidence suggests that the solar corona is heated impulsively, meaning that nanoflares may be ubiquitous in quiet and active regions (ARs). Hard X-ray (HXR) observations with unprecedented sensitivity >3 keV are now enabled by focusing instruments. We analyzed data from the Focusing Optics X-ray Solar Imager (FOXSI) rocket and the Nuclear Spectroscopic Telescope Array (NuSTAR) spacecraft to constrain properties of AR nanoflares simulated by the EBTEL field-line-averaged hydrodynamics code. We generated model X-ray spectra by computing differential emission measures for homogeneous nanoflare sequences with heating amplitudes H 0, durations τ, delay times between events t N , and filling factors f. The single quiescent AR observed by FOXSI-2 on 2014 December 11 is well fit by nanoflare sequences with heating amplitudes 0.02 erg cm−3 s−1 99% confidence for all regions observed by either instrument.