Browsing by Author "Tripathi, Durgesh"

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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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    OBSERVATIONS OF PLASMA UPFLOW IN A WARM LOOP WITH HINODE/EIS
    (The American Astronomical Society, 2012) Tripathi, Durgesh; Mason, Helen E.; Del Zanna, Giulio; Bradshaw, Steven
    A complete understanding of Doppler shift in active region loops can help probe the basic physical mechanism involved into the heating of those loops. Here, we present observations of upflows in coronal loops detected in a range of temperatures (log T = 5.8–6.2). The loop was not discernible above these temperatures. The speed of upflow was strongest at the footpoint and decreased with height. The upflow speed at the footpoint was about 20 km s−1 in Fe viii, which decreased with temperature, being about 13 km s−1 in Fe x, about 8 km s−1 in Fe xii, and about 4 km s−1 in Fe xiii. To the best of our knowledge, this is the first observation providing evidence of upflow of plasma in coronal loop structures at these temperatures. We interpret these observations as evidence of chromospheric evaporation in quasi-static coronal loops.