Prevalence of Thermal Non-Equilibrium over an Active Region

Abstract

Recent observations have shown that besides the characteristic multi-million degree component the corona also contains a large amount of cool material called coronal rain, whose clumps are 10 - 100 times cooler and denser than the surroundings and are often organised in larger events termed showers. Thermal instability (TI) within a coronal loop in a state of thermal non-equilibrium (TNE) is the leading mechanism behind the formation of coronal rain but no investigation on showers exists to date. In this study, we conduct a morphological and thermodynamic multi-wavelength study of coronal rain showers observed in an active region (AR) off-limb with IRIS and SDO, spanning chromospheric to transition region and coronal temperatures. Rain showers were found to be widespread across the AR over the 5.45-hour observing time, with average length, width and duration of 27.37$\pm$11.95 Mm, 2.14$\pm$0.74 Mm, and 35.22$\pm$20.35 min, respectively. We find a good correspondence between showers and the cooling coronal structures consistent with the TNE-TI scenario, thereby properly identifying coronal loops in the 'coronal veil', including the strong expansion at low heights and an almost zero expansion in the corona. This agrees with previous work suggesting that the observed zero expansion in the EUV is due to specific cross-field temperature distribution. We estimate the total number of showers to be 155$\pm$40, leading to a TNE volume of 4.56$\pm$3.71 $\times$ $10^{28}$cm${}^3$, i.e. on the same order of the AR volume. This suggests a prevalence of TNE over the AR indicating strongly stratified and high-frequency heating on average.

References in corpus (32)

• The Interface Region Imaging Spectrograph (IRIS)
• Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
• Multi-scale Gaussian normalization for solar image processing
• Observing the fine structure of loops through high resolution spectroscopic observations of coronal rain with the CRISP instrument at the Swedish Solar Telescope
• An Ab Initio approach to Solar Coronal Loops
• Solar Corona Loop Studies with AIA: I. Cross-Sectional Temperature Structure
• Structure of solar coronal loops: from miniature to large-scale
• Evidence for Widespread Cooling in an Active Region Observed with the SDO Atmospheric Imaging Assembly
• The multi-thermal and multi-stranded nature of coronal rain
• Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6~m New Solar Telescope
• Active region transition region loop populations and their relationship to the corona
• Multidimensional modeling of coronal rain dynamics
• Evidence for evaporation-incomplete condensation cycles in warm solar coronal loops
• Constant cross section of loops in the solar corona
• On the occurrence of thermal non-equilibrium in coronal loops
• Coronal rain in magnetic arcades: Rebound shocks, Limit cycles, and Shear flows
• On the Size of Structures in the Solar Corona
• Long-period intensity pulsations in the solar corona during activity cycle 23
• Coronal condensations caused by magnetic reconnection between solar coronal loops
• A model for the formation of the active region corona driven by magnetic flux emergence
• The Coronal Monsoon: Thermal Nonequilibrium Revealed by Periodic Coronal Rain
• Dynamics of coronal rain and descending plasma blobs in solar prominences: I. Fully ionised case
• The Role of Asymmetries in Thermal Non-Equilibrium
• The Coronal Veil
• Observing the formation of flare-driven coronal rain
• Coronal rain in randomly heated arcades
• Multi-scale observations of thermal non-equilibrium cycles in coronal loops
• Are constant loop widths an artifact of the background and the spatial resolution?
• Coronal Condensation as the Source of Transition Region Supersonic Downflows above a Sunspot
• Automated Spatiotemporal Analysis of Fibrils and Coronal Rain using the Rolling Hough Transform
• Coronal Temperature Maps from Solar EUV images: a Blind Source Separation Approach
• Magnetohydrodynamic spectroscopy of a non-adiabatic solar atmosphere

Cited by in corpus (10)

• Spatial and Temporal Analysis of Quiescent Coronal Rain over an Active Region
• EUV fine structure and variability associated with coronal rain revealed by Solar Orbiter/EUI HRIEUV and SPICE
• From Chromospheric Evaporation to Coronal Rain: An Investigation of the Mass and Energy Cycle of a Flare
• Impact of thermal misbalance on acoustic-gravity waves in the solar atmosphere
• Simulating stellar coronal rain and slingshot prominences
• Can we rely on EUV emission to identify coronal waveguides?
• Understanding coronal rain dynamics through a point-mass model
• Damping of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere
• Structure and dynamics of erupting solar prominences using the Rolling Hough Transform: Toward a feature-oriented classification
• Thermal Non-equilibrium Cycles in a Non-eruptive Pseudo-Streamer