http://arxiv.org/abs/2203.04385
In coronal loop modeling, it is commonly assumed that the loops are semi-circular with a uniform cross-sectional area. However, observed loops are rarely semi-circular, and extrapolations of the magnetic field show that the field strength decreases with height, implying that the cross-sectional area should expand with height. In this work, we examine these two assumptions directly to understand how they affect the hydrodynamic and radiative response to strong, impulsive heating events. Both the magnitude and rate of area expansion impact the dynamics directly, and we show that an expanding cross-section significantly lengthens the time for a loop to cool and drain, increases upflow durations, and suppresses sound waves. An increase in the eccentricity of loops, on the other hand, only increases the draining timescale, and is a minor effect in general. Spectral line intensities are also strongly impacted by the variation in the cross-sectional area since they depend on both the volume of the emitting region as well as the density and ionization state. With a larger expansion, the density is reduced, so the lines at all heights are relatively reduced in intensity and, because of the increase of cooling times, the hottest lines remain bright for significantly longer. Future modeling work needs to include area expansion for an accurate picture of the hydrodynamics, and future observations are needed to provide tighter constraints on the magnitude, rate, and location of the expansion or lack thereof.
J. Reep, I. Ugarte-Urra, H. Warren, et. al.
Thu, 10 Mar 22
20/60
Comments: Submitted to ApJ. Comments and criticisms welcome!
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