The Role of Asymmetries in Thermal Nonequilibrium

Klimchuk, J. A.; Luna, M.

doi:10.3847/1538-4357/ab41f4

Cited by 43 publications

(71 citation statements)

References 42 publications

(60 reference statements)

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“…However, stratified and high frequency heating can be present beyond structures that are experiencing TNE, as shown in Froment et al (2018). In some cases, close to TNE-prone conditions, the loops global behaviour can be dominated by siphon flows without thermal cycles ( also see Klimchuk & Luna 2019). Future studies ought to determine if the spatiotemporal structure of the heating in active regions, such as the one studied in the present paper, can be understood by a distribution of stratifications and heating frequencies.…”

Section: Multi-scale Tne Cyclesmentioning

confidence: 85%

Multi-scale observations of thermal non-equilibrium cycles in coronal loops

Froment

Antolin

Henriques

et al. 2019

A&A

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Context. Thermal non-equilibrium (TNE) is a phenomenon that can occur in solar coronal loops when the heating is quasi-constant and highly-stratified. Under such heating conditions, coronal loops undergo cycles of evaporation and condensation. The recent observations of ubiquitous long-period intensity pulsations in coronal loops and their relationship with coronal rain have demonstrated that understanding the characteristics of TNE cycles is an essential step in constraining the circulation of mass and energy in the corona. Aims. We report unique observations with the Solar Dynamics Observatory (SDO) and the Swedish 1-m Solar Telescope (SST) that link the captured thermal properties across the extreme spatiotemporal scales covered by TNE processes. Methods. Within the same coronal loop bundle, we captured 6 hr period coronal intensity pulsations in SDO/AIA and coronal rain observed off-limb in the chromospheric Hα and Ca II K spectral lines with SST/CRISP and SST/CHROMIS. We combined a multithermal analysis of the cycles with AIA and an extensive spectral characterisation of the rain clumps with the SST. Results. We find clear evidence of evaporation-condensation cycles in the corona which are linked with periodic coronal rain showers. The high-resolution spectroscopic instruments at the SST reveal the fine-structured rain strands and allow us to probe the cooling phase of one of the cycles down to chromospheric temperatures. Conclusions. These observations reinforce the link between long-period intensity pulsations and coronal rain. They also demonstrate the capability of TNE to shape the dynamics of active regions on the large scales as well as on the smallest scales currently resolvable.

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Section: Multi-scale Tne Cyclesmentioning

confidence: 85%

Multi-scale observations of thermal non-equilibrium cycles in coronal loops

Froment

Antolin

Henriques

et al. 2019

A&A

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“…As dynamic magnetic structures, a variety of formation processes have been proposed and modelled which can result in prominence structures. Examples of proposed formation processes include photospheric shearing motions (Zuccarello et al 2015), and asymmetries in heating and structure which result in steady flows into asymmetrical loops (Klimchuk & Luna 2019). They have even been modelled as dynamic threads not requiring loops, where thermal non-equilibrium mechanisms result in quasi-static structures (Karpen et al 2001).…”

Section: Introductionmentioning

confidence: 99%

Amplification of magnetic field twisting by a stagnation point flow

Sumner

Taroyan

2020

A&A

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Context. Flows are a common feature of many processes occurring in the solar atmosphere, such as the formation of prominences where evaporated plasma from the chromosphere condensates along thin prominence threads that are seen to twist and oscillate. Aim. We aim to investigate the twisting of these threads by plasma condensation during their formation. Methods. We introduce a simple model with fixed critical points where the flow speed matches the Alfvén speed. This allows us to study the problem separately in the sub-Alfvénic and super-Alfvénic regimes. The temporal and spatial evolution of small amplitude initial twists along a thread is investigated analytically and numerically. Results. Analytical solutions are constructed in terms of the generalised hypergeometric functions. The solutions grow in time, despite the absence of any influxes of energy or magnetic fields. These results are confirmed numerically: We find oscillations with an amplifying amplitude and increasing period in the sub-Alfvénic regime. In the super-Alfvénic regime, we find twist amplification without any accompanying oscillations. An interesting result is the convergence of the twists at the critical points that leads to the formation of steep gradients and small scales. Energy is transferred from the flow to the amplifying twists. Conclusions. Magnetic field lines may be twisted by a stagnation point flow without the influx of any azimuthal field or energy. This twisting could assist in the formation of topology that is able to support the growth of prominences. The formation of steep gradients and small scales at the critical point is a new phenomenon which requires further investigation in the non-linear regime with the inclusion of magnetic diffusion.

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“…TNE loops have significant evaporative upflows in both legs, and they are energetically important. For example, at the time when the temperature profile is flat in the base model of Klimchuk and Luna (2019, black curve in Fig. 6), the heating from the divergence of the enthalpy flux is nearly equal to radiative cooling, with coronal heating being much smaller than either (at the apex).…”

Section: Growing Perturbations During a Tne Cyclementioning

confidence: 99%

The Distinction Between Thermal Nonequilibrium and Thermal Instability

Klimchuk

2019

Sol Phys

Self Cite

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For some forms of steady heating, coronal loops are in a state of thermal nonequilibrium and evolve in a manner that includes accelerated cooling, often resulting in the formation of a cold condensation. This is frequently confused with thermal instability, but the two are in fact fundamentally different. We explain the distinction and discuss situations where they may be interconnected. Large-amplitude perturbations, perhaps associated with MHD waves, likely play a role in explaining phenomena that have been attributed to thermal nonequilibrium but also seem to require cross-field communication.

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The Role of Asymmetries in Thermal Nonequilibrium

Cited by 43 publications

References 42 publications

Multi-scale observations of thermal non-equilibrium cycles in coronal loops

Multi-scale observations of thermal non-equilibrium cycles in coronal loops

Amplification of magnetic field twisting by a stagnation point flow

The Distinction Between Thermal Nonequilibrium and Thermal Instability

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