ALMA observations of transient heating in a solar active region

Santos, J. M. da Silva; Rodríguez, J. de la Cruz; White, S. M.; Leenaarts, J.; Vissers, G. J. M.; Hansteen, V. H.

doi:10.1051/0004-6361/202038755

Cited by 16 publications

(17 citation statements)

References 103 publications

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“…Their typical duration was from about 55 to 125 s. Eklund et al (2020) reported that the properties of several of their events were consistent with the signatures of propagating shock waves (see also the simulations presented in Eklund et al 2021). Finally, we mention that transient brightenings in 3 mm ALMA observations of a small active region have been reported by da Silva Santos et al (2020). Their events corresponded to much higher excess brightness temperatures (up to about 14200 K) than the quiet Sun events of Paper II.…”

Section: Introductionsupporting

confidence: 64%

ALMA observations of the variability of the quiet Sun at millimeter wavelengths

Nindos,

Patsourakos,

Alissandrakis

et al. 2021

Preprint

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Aims. We address the variability of the quiet solar chromosphere at 1.26 mm and 3 mm with a focus on the study of spatially resolved oscillations and transient brightenings, i.e. small, weak events of energy release. Both phenomena may have a bearing on the heating of the chromosphere. Methods. We used Atacama Large Millimeter/submillimeter Array (ALMA) observations of the quiet Sun at 1.26 mm and 3 mm. The spatial and temporal resolution of the data were 1 − 2 and 1 s, respectively. The concatenation of light curves from different scans yielded a frequency resolution in spectral power of 0.5-0.6 mHz. At 1.26 mm, in addition to power spectra of the original data, we degraded the images to the spatial resolution of the 3 mm images and used fields of view of equal area for both data sets. The detection of transient brightenings was made after the effect of oscillations was removed. Results. At both frequencies we detected p-mode oscillations in the range 3.6-4.4 mHz. The corrections for spatial resolution and field of view at 1.26 mm decreased the rms of the oscillations by factors of 1.6 and 1.1, respectively. In the corrected data sets, the oscillations at 1.26 mm and 3 mm showed brightness temperature fluctuations of ∼1-7-1.8% with respect to the average quiet Sun, corresponding to 137 and 107 K, respectively. We detected 77 transient brightenings at 1.26 mm and 115 at 3 mm. Although their majority occurred in cell interior, the occurrence rate per unit area of the 1.26 mm events was higher than that of the 3 mm events and this conclusion does not change if we take into account differences in spatial resolution and noise levels. The energy associated with the transient brightenings ranged from 1.8 × 10 23 to 1.1 × 10 26 erg and from 7.2 × 10 23 to 1.7 × 10 26 erg for the 1.26 mm and 3 mm events, respectively. The corresponding power-law indices of the energy distribution were 1.64 and 1.73. We also found that ALMA bright network structures corresponded to dark mottles/spicules seen in broadband Hα images from the GONG network. Conclusions. The fluctuations associated with the p-mode oscillations represented a fraction of 0.55-0.68 of the full power spectrum. Their energy density at 1.26 mm was 3×10 −2 erg cm −3 . The computed low-end energy of the 1.26 mm transient brightenings is among the smallest ever reported, irrespective of the wavelength of observation. Although the occurrence rate per unit area of the 1.26 mm transient brightenings was higher than that of the 3 mm events their power per unit area is smaller probably due to the detection of many weak 1.26 mm events.

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Section: Introductionsupporting

confidence: 64%

ALMA observations of the variability of the quiet Sun at millimeter wavelengths

Nindos,

Patsourakos,

Alissandrakis

et al. 2021

Preprint

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“…UVBs (Peter et al 2014) are compact transient brightenings observed in UV bands, with very complex Si iv profiles, and do not generally show a co-spatial brightening in the coronal channels of the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) instrument. Similar targets have been studied with recent simulations (Danilovic 2017;Hansteen et al 2017Hansteen et al , 2019Libbrecht et al 2020) and observations (Socas-Navarro et al 2006;Toriumi et al 2017;Libbrecht et al 2017;Guglielmino et al 2018;Smitha et al 2018;Vissers et al 2019;Yadav et al 2019;Ortiz et al 2020;da Silva Santos et al 2020). Microflares or stronger events show a visible response in coronal channels and they would originate from or extend into higher layers.…”

Section: Introductionmentioning

confidence: 62%

“…Our inversion is not sensitive to temperatures above approximately 10,000 K so we cannot set constraints on the height where the heating observed in AIA is located. A coronal response is not normally seen in photospheric/low-chromospheric reconnection events such as Ellerman bombs, but heating to transition-region temperatures in reconnection events higher in the chromosphere can give a response in AIA if the column density of overlying cool material is low enough so that not all radiation is absorbed in the hydrogen and helium continua (Young et al 2018;Guglielmino et al 2019;Hansteen et al 2019;da Silva Santos et al 2020).…”

Section: Discussionmentioning

confidence: 99%

An observationally constrained model of strong magnetic reconnection in the solar chromosphere

Baso

Rodríguez

2021

A&A

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Context. The evolution of the photospheric magnetic field plays a key role in the energy transport into the chromosphere and the corona. In active regions, newly emerging magnetic flux interacts with the pre-existent magnetic field, which can lead to reconnection events that convert magnetic energy into thermal energy. Aims. We aim to study the heating caused by a strong reconnection event that was triggered by magnetic flux cancelation. Methods. We use imaging and spectropolarimetric data in the Fe I 6301& 6302 Å, Ca II 8542 Å, and Ca II K spectral lines obtained with the CRISP and CHROMIS instruments at the Swedish 1-m Solar Telescope. These data were inverted with the STiC code by performing multi-atom, multi-line, non-local thermodynamic equilibrium inversions. These inversions yielded a three-dimensional model of the reconnection event and surrounding atmosphere, including temperature, velocity, microturbulence, magnetic field, and radiative loss rate. Results. The model atmosphere shows the emergence of magnetic loops with a size of several arcseconds into a pre-existing predominantly unipolar field. Where the reconnection region is expected to be, we see an increase in the chromospheric temperature of roughly 2000 K as well as bidirectional flows of the order of 10 km s−1 emanating from there. We see bright blobs of roughly 0.2 arcsec in diameter in the Ca II K, moving at a plane-of-the-sky velocity of the order of 100 km s−1 and a blueshift of 100 km s−1, which we interpret as ejected plasmoids from the same region. This scenario is consistent with theoretical reconnection models, and therefore provides evidence of a reconnection event taking place. The chromospheric radiative losses at the reconnection site are as high as 160 kW m−2, providing a quantitative constraint on theoretical models that aim to simulate reconnection caused by flux emergence in the chromosphere.

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“…The ALMA intensity can be interpreted as brightness temperature under the Rayleigh-Jeans limit (Wedemeyer et al 2016). Hence, ALMA is a valuable tool to study the thermal structure of the chromosphere (some recent results include Shimojo et al 2017;Loukitcheva et al 2019;da Silva Santos et al 2020).…”

Section: Alma Observationsmentioning

confidence: 99%

High-frequency wave power observed in the solar chromosphere with IBIS and ALMA

Molnar,

Reardon,

Cranmer

et al. 2021

Preprint

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We present observational constraints on the chromospheric heating contribution from acoustic waves with frequencies between 5 and 50 mHz. We utilize observations from the Dunn Solar Telescope in New Mexico complemented with observations from the Atacama Large Millimeter Array collected on 2017 April 23. The properties of the power spectra of the various quantities are derived from the spectral lines of Ca II 854.2 nm, H I 656.3 nm, and the millimeter continuum at 1.25 mm and 3 mm. At the observed frequencies the diagnostics almost all show a power law behavior, whose particulars (slope, peak and white noise floors) are correlated with the type of solar feature (internetwork, network, plage). In order to disentangle the vertical versus transverse plasma motions we examine two different fields of view; one near disk center and the other close to the limb. To infer the acoustic flux in the middle chromosphere, we compare our observations with synthetic observables from the timedependent radiative hydrodynamic RADYN code. Our findings show that acoustic waves carry up to about 1 kW m −2 of energy flux in the middle chromosphere, which is not enough to maintain the quiet chromosphere, contrary to previous publications.

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ALMA observations of transient heating in a solar active region

Cited by 16 publications

References 103 publications

ALMA observations of the variability of the quiet Sun at millimeter wavelengths

ALMA observations of the variability of the quiet Sun at millimeter wavelengths

An observationally constrained model of strong magnetic reconnection in the solar chromosphere

High-frequency wave power observed in the solar chromosphere with IBIS and ALMA

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