The multi-thermal chromosphere

Santos, J. M. da Silva; Rodríguez, J. de la Cruz; Leenaarts, J.; Chintzoglou, Georgios; Pontieu, Bart De; Wedemeyer, Sven; Szydlarski, Mikołaj

doi:10.1051/0004-6361/201937117

Cited by 37 publications

(30 citation statements)

References 81 publications

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“…(h) D8 dataset: ALMA Band 6, 22 April 2017 (figure 8) This dataset (also appeared in da Silva Santos et al [94], and Chintzoglou et al [95]) samples the same plage region as in D2, but here, in Band 6 with a smaller FOV, observed about 80 min earlier than D2/Band-3 (table 1). Thus, the field geometries (at around the mid-to-high chromosphere) is also very similar to that of D2, i.e.…”

Section: Analysis and Resultsmentioning

confidence: 73%

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 Resultsmentioning

confidence: 73%

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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“…Other ALMA observations have shown bright fibril-like structures emanating from magnetic concentrations (Molnar et al 2019;da Silva Santos et al 2020;Chintzoglou et al 2020). These features contrast with the weakly magnetized areas in the left-hand side of the FOV that shows lower amplitude variations of T b .…”

Section: Overviewmentioning

confidence: 88%

“…However, recent studies that used some of the first solar ALMA observations brought up the need to better understand the formation heights of the ALMA bands in active regions (Loukitcheva et al 2017;da Silva Santos et al 2020;Chintzoglou et al 2020) as they likely differ from the quiet Sun (QS) where the emission is dominated by acoustic shocks (e.g., White et al 2006;Wedemeyer-Böhm et al 2007;Patsourakos et al 2020). Moreover, the contribution functions of the mm continuum may also depend on nonequilibrium ionization/recombination effects in the chromosphere (e.g., Carlsson & Stein 2002;Leenaarts & Wedemeyer-Böhm 2006;Rutten 2017;Martínez-Sykora et al 2020a).…”

Section: Introductionmentioning

confidence: 99%

ALMA observations of transient heating in a solar active region

Santos

Rodríguez

White

et al. 2020

A&A

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Aims. We aim to investigate the temperature enhancements and formation heights of solar active-region brightenings such as Ellerman bombs (EBs), ultraviolet bursts (UVBs), and flaring active-region fibrils (FAFs) using interferometric observations in the millimeter (mm) continuum provided by the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. We examined 3 mm signatures of heating events identified in Solar Dynamics Observatory observations of an active region and compared the results with synthetic spectra from a 3D radiative magnetohydrodynamic simulation. We estimated the contribution from the corona to the mm brightness using differential emission measure analysis. Results. We report the null detection of EBs in the 3 mm continuum at ∼1.2″ spatial resolution, which is evidence that they are sub-canopy events that do not significantly contribute to heating the upper chromosphere. In contrast, we find the active region to be populated with multiple compact, bright, flickering mm-bursts – reminiscent of UVBs. The high brightness temperatures of up to ∼14 200 K in some events have a contribution (up to ∼7%) from the corona. We also detect FAF-like events in the 3 mm continuum. These events show rapid motions of > 10 kK plasma launched with high plane-of-sky velocities (37 − 340 km s−1) from bright kernels. The mm FAFs are the brightest class of warm canopy fibrils that connect magnetic regions of opposite polarities. The simulation confirms that ALMA should be able to detect the mm counterparts of UVBs and small flares and thus provide a complementary diagnostic for localized heating in the solar chromosphere.

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“…While the first regular ALMA observations of the Sun were only offered in Cycle 4 with a first solar campaign in December 2016, earlier observations from Commissioning and Science Verification (CSV) campaigns have been made publicly available. Both regular and CSV data are already used in publications: Alissandrakis et al (2017), Bastian et al (2017), Shimojo et al (2017b), Brajša et al (2018), Nindos et al (2018), Yokoyama et al (2018), Jafarzadeh et al (2019), Loukitcheva et al (2019), Molnar et al (2019), Rodger et al (2019), Selhorst et al (2019), Patsourakos et al (2020), da Silva Santos et al (2020.…”

Section: Introductionmentioning

confidence: 99%

The Sun at millimeter wavelengths

Wedemeyer

Szydlarski

Jafarzadeh

et al. 2020

A&A

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Context. The Atacama Large Millimeter/submillimeter Array (ALMA) started regular observations of the Sun in 2016, first offering receiver Band 3 at wavelengths near 3 mm (100 GHz) and Band 6 at wavelengths around 1.25 mm (239 GHz). Aims. Here we present an initial study of one of the first ALMA Band 3 observations of the Sun. Our aim is to characterise the diagnostic potential of brightness temperatures measured with ALMA on the Sun. Methods. The observation covers a duration of 48 min at a cadence of 2 s targeting a quiet Sun region at disc-centre. Corresponding time series of brightness temperature maps are constructed with the first version of the Solar ALMA Pipeline and compared to simultaneous observations with the Solar Dynamics Observatory (SDO). Results. The angular resolution of the observations is set by the synthesised beam, an elliptical Gaussian that is approximately 1.4″ × 2.1″ in size. The ALMA maps exhibit network patches, internetwork regions, and elongated thin features that are connected to large-scale magnetic loops, as confirmed by a comparison with SDO maps. The ALMA Band 3 maps correlate best with the SDO/AIA 171 Å, 131 Å, and 304 Å channels in that they exhibit network features and, although very weak in the ALMA maps, imprints of large-scale loops. A group of compact magnetic loops is very clearly visible in ALMA Band 3. The brightness temperatures in the loop tops reach values of about 8000−9000 K and in extreme moments up to 10 000 K. Conclusions. ALMA Band 3 interferometric observations from early observing cycles already reveal temperature differences in the solar chromosphere. The weak imprint of magnetic loops and the correlation with the 171, 131, and 304 SDO channels suggests, however, that the radiation mapped in ALMA Band 3 might have contributions from a wider range of atmospheric heights than previously assumed, but the exact formation height of Band 3 needs to be investigated in more detail. The absolute brightness temperature scale as set by total power measurements remains less certain and must be improved in the future. Despite these complications and the limited angular resolution, ALMA Band 3 observations have a large potential for quantitative studies of the small-scale structure and dynamics of the solar chromosphere.

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The multi-thermal chromosphere

Cited by 37 publications

References 81 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

ALMA observations of transient heating in a solar active region

The Sun at millimeter wavelengths

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