Explaining Inverted-Temperature Loops in the Quiet Solar Corona With Magnetohydrodynamic Wave-Mode Conversion

Abstract

Coronal loops trace out bipolar, arch-like magnetic fields above the Sun's surface. Recent measurements that combine rotational tomography, extreme ultraviolet imaging, and potential-field extrapolation have shown the existence of large loops with inverted temperature profiles; i.e., loops for which the apex temperature is a local minimum, not a maximum. These "down loops" appear to exist primarily in equatorial quiet regions near solar minimum. We simulate both these and the more prevalent large-scale "up loops" by modeling coronal heating as a time-steady superposition of: (1) dissipation of incompressible Alfvén-wave turbulence, and (2) dissipation of compressive waves formed by mode conversion from the initial population of Alfvén waves. We found that when a large percentage (> 99%) of the Alfvén waves undergo this conversion, heating is greatly concentrated at the footpoints and stable "down loops" are created. In some cases we found loops with three maxima that are also gravitationally stable. Models that agree with the tomographic temperature data exhibit higher gas pressures for "down loops" than for "up loops," which is consistent with observations. These models also show a narrow range of Alfvén wave amplitudes: 3 to 6 km s −1 at the coronal base. This is low in comparison to typical observed amplitudes of 20 to 30 km s −1 in bright X-ray loops. However, the large-scale loops we model are believed to comprise a weaker diffuse background that fills much of the volume of the corona. By constraining the physics of loops that underlie quiescent streamers, we hope to better understand the formation of the slow solar wind.

Energy Input Flux in the Global Quiet-Sun Corona

“…DEMT studies provide a time-averaged description of the state of the corona during the observing time of each structure (∼ 1/2 solar rotation). The new results of this study are to be interpreted in this context, and can be compared with steady-state models of largescale coronal structures, such as those recently developed by Schiff & Cranmer (2016), who sucessfully reproduced the up/down loops reported by Huang et al (2012); Nuevo et al (2013), and studied here in Section 5.3.…”

“…Down loops were first predicted by Serio et al (1981), and later on by Aschwanden & Schrijver (2002). In a recent study by Schiff & Cranmer (2016), down and up loops have been successfully reproduced by a numerical implementation of a 1D steady state model that considers time-averaged heating rates. The analysis of these structures in the context of the new tool here developed is shown in Section 5.3 below.…”

Magnetic Tornado Properties: A Substantial Contribution to the Solar Coronal Heating via Efficient Energy Transfer

“…We note that flux emergence is an alternative candidate for the coronal heat source (Schrijver et al 1998;Wang 2020Wang , 2022. For energy dissipation, several mechanisms are proposed, including magnetic-field braiding (Parker 1972(Parker , 1983(Parker , 1988Sturrock & Uchida 1981;Berger 1991), resonant absorption (Erdelyi & Goossens 1995;Terradas et al 2010;Goossens et al 2011), phase mixing (Heyvaerts & Priest 1983;De Moortel et al 2000;Goossens et al 2012), shock formation (Moriyasu et al 2004;Antolin et al 2008;Schiff & Cranmer 2016), and turbulence (van Ballegooijen et al 2011(van Ballegooijen et al , 2014Matsumoto 2018;Shoda & Takasao 2021). From the observational point of view, coronal heating is often discussed in terms of thermal response, in particular the differential emission measure (e.g., Aschwanden & Parnell 2002;Warren et al 2012;Shoda & Takasao 2021).…”

Three‐Dimensional Structure of the Corona During WHPI Campaign Rotations CR‐2219 and CR‐2223

“…Such structures are expected where heating is strongly enhanced at the coronal base. This has been explored by Schiff and Cranmer (2016), who used a 1D model to simulate down loops by including coronal heating dissipation of compressive waves formed by mode conversion from an initial population of Alfvén waves, a physical mechanism originally proposed by Nuevo et al (2013). Second, as in previous DEMT studies, the reconstructions reveal that the coronal plasma is ubiquitously characterized by a significant local temperature spread within the ∼10 4 km linear size of the tomography computational cell (Vásquez, 2016).…”

“…Such structures are expected where heating is strongly enhanced at the coronal base. This has been explored by Schiff and Cranmer (2016), who used a 1D model to simulate down loops by including coronal heating dissipation of compressive waves formed by mode conversion from an initial population of Alfvén waves, a physical mechanism originally proposed by Nuevo et al. (2013).…”