Active Region Coronal Rain Event Observed by the Fast Imaging Solar Spectrograph on the NST

Ahn, Kwangsu; Chae, Jongchul; Cho, Kyung-Suk; Song, Donguk; Yang, Heesu; Goode, Philip R.; Cao, Wenda; Park, Hyungmin; Nah, Jakyoung; Jang, Bi-Ho; Park, Young Deuk

doi:10.1007/s11207-014-0559-x

Cited by 33 publications

(37 citation statements)

References 28 publications

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“…neutral and ionized species falling in unison. This co-spatiality of neutral and ionized material has been observed in Hα and He II 304Å (De Groof et al 2004, in Hα and Ca II 8542Å (Ahn et al 2014), and in Hα and Ca II H (Chae 2010). The last observation corresponds to cool emission features in a hedgerow prominence.…”

supporting

confidence: 55%

Dynamics of Coronal Rain and Descending Plasma Blobs in Solar Prominences. Ii. Partially Ionized Case

Oliver¹,

Soler²,

Terradas³

et al. 2016

ApJ

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Coronal rain clumps and prominence knots are dense condensations with chromospheric to transition region temperatures that fall down in the much hotter corona. Their typical speeds are in the range 30-150 km s −1 and of the order of 10-30 km s −1 , respectively, i.e., they are considerably smaller than free fall velocities. These cold blobs contain a mixture of ionized and neutral material that must be dynamically coupled in order to fall together, as observed. We investigate this coupling by means of hydrodynamic simulations in which the coupling arises from the friction between ions and neutrals. The numerical simulations presented here are an extension of those of Oliver et al. (2014) to the partially ionized case. We find that, although the relative drift speed between the two species is smaller than 1 m s −1 at the blob center, it is sufficient to produce the forces required to strongly couple charged particles and neutrals. The ionization degree has no discernible effect on the main results of our previous work for a fully ionized plasma: the condensation has an initial acceleration phase followed by a period with roughly constant velocity and, in addition, the maximum descending speed is clearly correlated with the ratio of initial blob to environment density.

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supporting

confidence: 55%

Dynamics of Coronal Rain and Descending Plasma Blobs in Solar Prominences. Ii. Partially Ionized Case

Oliver¹,

Soler²,

Terradas³

et al. 2016

ApJ

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“…Coronal rain has been measured with temperatures ranging between 3000 K to 150 000 K (Levine & Withbroe 1977;Müller et al 2005) and is expected from simulations to have a density of 10 16 -10 18 m −3 (Antolin et al 2010;Luna et al 2012;Fang et al 2013Fang et al , 2015; this value is confirmed by observations (Antolin et al 2015). The downflow speed of the rain ranges between 30 up to supersonic speeds of 200 km s −1 with an average of 60−70 km s −1 (Ahn et al 2014;Kleint et al 2014;Antolin et al 2015;Straus et al 2015).…”

Section: Introductionmentioning

confidence: 59%

Kinematics of coronal rain in a transversely oscillating loop: Ponderomotive force and rain-excited oscillations

Verwichte

Antolin

Rowlands

et al. 2017

A&A

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Context. Coronal rain is composed of cool dense blobs that form in solar coronal loops and are a manifestation of catastrophic cooling linked to thermal instability. Once formed, rain falls towards the solar surface at sub-ballistic speeds, which is not well understood. Pressure forces seem to be the prime candidate to explain this. In many observations rain is accompanied by transverse oscillations and the interaction between rain and these oscillations needs to be explored. Aims. Therefore, an alternative kinematic model for coronal rain kinematics in transversely oscillating loops is developed to understand the physical nature of the observed sub-ballistic falling motion of rain. This model explicitly explores the role of the ponderomotive force arising from the transverse oscillation on the rain motion and the capacity of rain to excite wave motion.Methods. An analytical model is presented that describes a rain blob guided by the coronal magnetic field supporting a onedimensional shear Alfvén wave as a point mass on an oscillating string. The model includes gravity and the ponderomotive force from the oscillation acting on the mass and the inertia of the mass acting on the oscillation. Results. The kinematics of rain in the limit of negligible rain mass are explored and falling and trapped regimes are found, depending on wave amplitude. In the trapped regime for the fundamental mode, the rain blob bounces back and forth around the loop top at a long period that is inversely proportional to the oscillation amplitude. The model is compared with several observational rain studies, including one in-depth comparison with an observation that shows rain with up-and-down bobbing motion. The role of rain inertia in exciting transverse oscillations is explored in inclined loops. Conclusions. It is found that the model requires displacement amplitudes of the transverse oscillation that are typically an order of magnitude larger than observed to explain the measured sub-ballistic motion of the rain. Therefore, it is concluded that the ponderomotive force is not the primary reason for understanding sub-ballistic motion, but it plays a role in cases of large loop oscillations. The appearance of rain causes the excitation of small-amplitude transverse oscillations that may explain observed events and provide a seismological tool to measure rain mass.

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“…While the relative high atomic mass of Calcium (factor of 40 compared to Hydrogen) does not allow us to extract directly an estimate of the temperature, we can take advantage of this mass difference to compute temperatures by combining Hα and Ca II K measurements. We thus achieve more precision by estimating the non-thermal broadening term, as in Ahn et al (2014), for example.…”

Section: Methodsmentioning

confidence: 99%

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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Active Region Coronal Rain Event Observed by the Fast Imaging Solar Spectrograph on the NST

Cited by 33 publications

References 28 publications

Dynamics of Coronal Rain and Descending Plasma Blobs in Solar Prominences. Ii. Partially Ionized Case

Dynamics of Coronal Rain and Descending Plasma Blobs in Solar Prominences. Ii. Partially Ionized Case

Kinematics of coronal rain in a transversely oscillating loop: Ponderomotive force and rain-excited oscillations

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

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