Modeling the quiet Sun cell and network emission with ALMA

Alissandrakis, C. E.; Nindos, A.; Bastian, T. S.; Patsourakos, S.

doi:10.1051/0004-6361/202038461

Cited by 20 publications

(21 citation statements)

References 31 publications

(41 reference statements)

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“…This observation (also studied in Alissandrakis et al [93]) represents the most quiescent solar region among our sample. ALMA’s FOV (and its immediate vicinity) includes several small magnetic concentrations, which seem to form some relatively weak network and internetwork areas.…”

Section: Analysis and Resultssupporting

confidence: 69%

An overall view of temperature oscillations in the solar chromosphere with ALMA

Jafarzadeh

Wedemeyer

Fleck

et al. 2020

Phil. Trans. R. Soc. A.

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By direct measurements of the gas temperature, the Atacama Large Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic tool to study the solar chromosphere. Here, we present an overview of the brightness-temperature fluctuations from several high-quality and high-temporal-resolution (i.e. 1 and 2 s cadence) time series of images obtained during the first 2 years of solar observations with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz) and 1.25 mm (239 GHz), respectively. The various datasets represent solar regions with different levels of magnetic flux. We perform fast Fourier and Lomb–Scargle transforms to measure both the spatial structuring of dominant frequencies and the average global frequency distributions of the oscillations (i.e. averaged over the entire field of view). We find that the observed frequencies significantly vary from one dataset to another, which is discussed in terms of the solar regions captured by the observations (i.e. linked to their underlying magnetic topology). While the presence of enhanced power within the frequency range 3–5 mHz is found for the most magnetically quiescent datasets, lower frequencies dominate when there is significant influence from strong underlying magnetic field concentrations (present inside and/or in the immediate vicinity of the observed field of view). We discuss here a number of reasons which could possibly contribute to the power suppression at around 5.5 mHz in the ALMA observations. However, it remains unclear how other chromospheric diagnostics (with an exception of H α line-core intensity) are unaffected by similar effects, i.e. they show very pronounced 3-min oscillations dominating the dynamics of the chromosphere, whereas only a very small fraction of all the pixels in the 10 ALMA datasets analysed here show peak power near 5.5 mHz. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

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Section: Analysis and Resultssupporting

confidence: 69%

An overall view of temperature oscillations in the solar chromosphere with ALMA

Jafarzadeh

Wedemeyer

Fleck

et al. 2020

Phil. Trans. R. Soc. A.

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“…The solar radius results (Table 1) indicated that the half-power method yield larger radius values when compared to the inflectionpoint method -the values derived from ALMA maps are about 1 larger, while the ones derived from SST maps are about 10 larger. Also, the inflection-point method radii are closer to the radius measurements reported in the literature (Selhorst et al 2019a;Alissandrakis et al 2020;Menezes et al 2021). Moreover, considering the uncertainties, the radii are in agreement with the SSC model radius predictions, R ssc and 𝑅 conv ssc , except R ssc at 100 GHz and 𝑅 conv ssc at 212 GHz.…”

Section: Radius Determinationsupporting

confidence: 86%

Subterahertz Radius and Limb Brightening of the Sun Derived from SST and ALMA

Menezes,

Selhorst,

de Castro

et al. 2021

Preprint

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Measurements of the radius and limb brightening of the Sun provide important information about the solar atmosphere structure and temperature. The solar radius increases as the observation at radio frequency decreases, indicating that each emission originates higher in the atmosphere. Thus, different layers of the solar atmosphere can be probed by observing at multiple wavelengths. In this work, we determined the average radius and limb brightening at 100, 212, 230, and 405 GHz, using data from the Solar Submillimeter Telescope and ALMA's single-dish observations. For the first time, limb brightening values for frequencies of 212 and 405 GHz were estimated. At sub-THz frequencies, the observed limb brightening may affect the solar radius measurements. We use two different and well known approaches to determine the radius: the half-power method and the inflection-point method. We investigate how the antenna beam size and the limb brightening level, 𝐿𝐵, can affect the radius measurements using both methods. Our results showed that the inflection-point method is the least affected by these parameters, and should thus be used for solar radius estimates at radio wavelengths. The measured average radii are 968 ± 3 (100 GHz), 963 ± 3 (212 GHz), 963 ± 2 (230 GHz), and 963 ± 5 (405 GHz). Finally, we used forward modeling to estimate the ranges of 𝐿𝐵 of the solar disk resulting in 5%-19% (100 GHz), 2%-12% (212 GHz), 6%-18% (230 GHz), and 3%-17% (405 GHz). Both radius and limb brightening estimates agree with previous measurements reported in the literature.

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“…Finally, all snapshot images were combined with contemporaneous full-disk ALMA images in order to recover large spatial scales that are not available to the interferometer, and obtain absolute brightness temperature calibration. We note that the correction of the brightness temperature at the solar disk center deduced by Alissandrakis et al (2020) for ALMA Band 6 applies only to full disk images and not to the interferometric images, whose flux calibration is established via the ALMA Calibrator Device (see Shimojo et al 2017a for details).…”

Section: Data Reduction and Overall View Of The Observationsmentioning

confidence: 99%

“…Using observations of absorption lines formed at heights from about 130 to about 1000 km, Canfield and Musman (1973) found that the p-mode energy density decreases with height from 2 × 10 2 erg cm −3 at 130 km to to 4 × 10 −1 erg cm −3 at a height of 1000 km. Alissandrakis et al (2020) used full-disk ALMA images to detect the solar limb and derived an emission height of 2400±1700 km for Band 6, which is above the heights scanned by Canfield and Musman (1973). This implies that the decreasing trend in the p-mode energy density with height extends above 1000 km.…”

mentioning

confidence: 97%

“…where δT (equal to √ 2 times the temperature rms) is the temperature amplitude of the p-mode, T is the average temperature, c s is the sound speed and γ = 5/3. Substituting in Equations 3 and 4 the Band 6 fractional rms for Band 6 original data from Table 2 (this series corresponds to highest fractional rms) and ρ from the Fontenla et al (1993) FAL C model corresponding to the average quiet Sun temperature in Band 6 at disk center from Alissandrakis et al (2020) we obtained an energy density of ≈ 3 × 10 −2 erg cm −3 . Using observations of absorption lines formed at heights from about 130 to about 1000 km, Canfield and Musman (1973) found that the p-mode energy density decreases with height from 2 × 10 2 erg cm −3 at 130 km to to 4 × 10 −1 erg cm −3 at a height of 1000 km.…”

mentioning

confidence: 99%

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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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Modeling the quiet Sun cell and network emission with ALMA

Cited by 20 publications

References 31 publications

An overall view of temperature oscillations in the solar chromosphere with ALMA

An overall view of temperature oscillations in the solar chromosphere with ALMA

Subterahertz Radius and Limb Brightening of the Sun Derived from SST and ALMA

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

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