Spectroscopic detection of coronal plasma flows in loops undergoing thermal non-equilibrium cycles

Pelouze, Gabriel; Auchère, F.; Bocchialini, K.; Froment, C.; Parenti, S.; Soubrié, É.

doi:10.1051/0004-6361/201935872

Cited by 10 publications

(11 citation statements)

References 79 publications

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“…The repeating cycle corresponds to periods of evaporation of chromospheric material that accumulates within the loop and periods of drainage of part of the material inside the loop in the form of precipitation that falls along the magnetic field lines. These condensation-evaporation cycles have their extreme ultraviolet (EUV) observational counterparts in the long period EUV pulsations, which have been described in recent studies (see Pelouze et al 2020;Auchère et al 2016Auchère et al , 2018Froment et al 2020).…”

Section: Introductionmentioning

confidence: 77%

Magnetic field inference in active region coronal loops using coronal rain clumps

Kriginsky

Oliver

Antolin

et al. 2021

A&A

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Aims. We aim to infer information about the magnetic field in the low solar corona from coronal rain clumps using high-resolution spectropolarimetric observations in the Ca II 8542 Å line obtained with the Swedish 1 m Solar Telescope. Methods. The weak-field approximation (WFA) provides a simple tool to obtain the line-of-sight component of the magnetic field from spectropolarimetric observations. We adapted a method developed in a previous paper in order to assess the different conditions that must be satisfied in order to properly use the WFA for the data at hand. We also made use of velocity measurements in order to estimate the plane-of-the-sky magnetic field component, so that the magnetic field vector could be inferred. Results. We have inferred the magnetic field vector from a data set totalling 100 spectral scans in the Ca II 8542 Å line, containing an off-limb view of the lower portion of catastrophically cooled coronal loops in an active region. Our results, albeit limited by the cadence and signal-to-noise ratio of the data, suggest that magnetic field strengths of hundreds of Gauss, even reaching up to 1000 G, are omnipresent at coronal heights below 9 Mm from the visible limb. Our results are also compatible with the presence of larger magnetic field values such as those reported by previous works. However, for large magnetic fields, the Doppler width from coronal rain is not that much larger than the Zeeman width, thwarting the application of the WFA. Furthermore, we have determined the temperature, T, and microturbulent velocity, ξ, of coronal rain clumps and off-limb spicules present in the same data set, and we have found that the former ones have narrower T and ξ distributions, their average temperature is similar, and coronal rain has microturbulent velocities smaller than those of spicules.

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Section: Introductionmentioning

confidence: 77%

Magnetic field inference in active region coronal loops using coronal rain clumps

Kriginsky

Oliver

Antolin

et al. 2021

A&A

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“…Finally, flows develop during all TNE cycles, even if the plasma remains at coronal temperatures throughout the cycle and no condensation forms (Mikić et al 2013). The observation of such flows of plasma at coronal temperature was reported by Pelouze et al (2020).…”

Section: Introductionmentioning

confidence: 80%

The role of asymmetries in coronal rain formation during thermal non-equilibrium cycles

Pelouze

Auchère

Bocchialini

et al. 2022

A&A

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Context. Thermal non-equilibrium (TNE) produces several observables that can be used to constrain the spatial and temporal distribution of solar coronal heating. Its manifestations include prominence formation, coronal rain, and long-period intensity pulsations in coronal loops. The recent observation of abundant periodic coronal rain associated with intensity pulsations allowed for these two phenomena to be unified as the result of TNE condensation and evaporation cycles. On the other hand, many observed intensity pulsation events show little to no coronal rain formation. Aims. Our goal is to understand why some TNE cycles produce such abundant coronal rain, while others produce little to no rain. Methods. We reconstructed the geometry of the periodic coronal rain event, using images from the Extreme Ultraviolet Imager (EUVI) onboard the Solar Terrestrial Relations Observatory (STEREO), and magnetograms from the Helioseismic and Magnetic Imager (HMI). We then performed 1D hydrodynamic simulations of this event for different heating parameters and variations of the loop geometry (9000 simulations in total). We compared the resulting behaviour to simulations of TNE cycles that do not produce coronal rain. Results. Our simulations show that both prominences and TNE cycles (with and without coronal rain) can form within the same magnetic structure. We show that the formation of coronal rain during TNE cycles depends on the asymmetry of the loop and of the heating. Asymmetric loops are overall less likely to produce coronal rain, regardless of the heating. In symmetric loops, coronal rain forms when the heating is also symmetric. In asymmetric loops, rain forms only when the heating compensates for the asymmetry.

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“…On the other hand, observations with SST have revealed that these warm flows contain a large number of small cool chromospheric cores with densities on the order of 10 11 cm −3 or higher (see Figure 17, Antolin et al, 2015b;Froment et al, 2020), suggesting a tip-ofthe-iceberg clump distribution in which the bulk at smaller sizes may still be unresolved. Combined, these chromospheric and transition-region return flows to the solar surface show mass-flux values on the order of 1 -5 × 10 9 g s −1 (similar to prominences), suggesting that most of the material in the loop undergoes catastrophic cooling.…”

Section: Coronal Rainmentioning

confidence: 99%

“…Simulations have shown that the driver mechanism is very likely thermal non-equilibrium (Antiochos, DeVore, and Klimchuk, 1999;Froment et al, 2017Froment et al, , 2018. This scenario is presented by footpoint concentrated heating that is frequent enough (with a mean recurrent time less than the radiative cooling time), leading to cycles of heating and cooling (also known as evaporation and condensation cycles), with periodic EUV flows (Pelouze et al, 2020). Although globally the loop is in a non-equilibrium state, during the cooling stage thermal instability can set in to produce coronal rain (Antolin, 2020).…”

Section: Coronal Rainmentioning

confidence: 99%

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

et al. 2021

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The Interface Region Imaging Spectrograph (IRIS) has been obtaining near- and far-ultraviolet images and spectra of the solar atmosphere since July 2013. IRIS is the highest resolution observatory to provide seamless coverage of spectra and images from the photosphere into the low corona. The unique combination of near- and far-ultraviolet spectra and images at sub-arcsecond resolution and high cadence allows the tracing of mass and energy through the critical interface between the surface and the corona or solar wind. IRIS has enabled research into the fundamental physical processes thought to play a role in the low solar atmosphere such as ion–neutral interactions, magnetic reconnection, the generation, propagation, and dissipation of waves, the acceleration of non-thermal particles, and various small-scale instabilities. IRIS has provided insights into a wide range of phenomena including the discovery of non-thermal particles in coronal nano-flares, the formation and impact of spicules and other jets, resonant absorption and dissipation of Alfvénic waves, energy release and jet-like dynamics associated with braiding of magnetic-field lines, the role of turbulence and the tearing-mode instability in reconnection, the contribution of waves, turbulence, and non-thermal particles in the energy deposition during flares and smaller-scale events such as UV bursts, and the role of flux ropes and various other mechanisms in triggering and driving CMEs. IRIS observations have also been used to elucidate the physical mechanisms driving the solar irradiance that impacts Earth’s upper atmosphere, and the connections between solar and stellar physics. Advances in numerical modeling, inversion codes, and machine-learning techniques have played a key role. With the advent of exciting new instrumentation both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST) and the Atacama Large Millimeter/submillimeter Array (ALMA), and space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim to review new insights based on IRIS observations or related modeling, and highlight some of the outstanding challenges.

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Spectroscopic detection of coronal plasma flows in loops undergoing thermal non-equilibrium cycles

Cited by 10 publications

References 79 publications

Magnetic field inference in active region coronal loops using coronal rain clumps

Magnetic field inference in active region coronal loops using coronal rain clumps

The role of asymmetries in coronal rain formation during thermal non-equilibrium cycles

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

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