ALMA Observations of the Solar Chromosphere on the Polar Limb

Yokoyama, T.; Shimojo, Masataka; Okamoto, Takenori J.; Iijima, Haruhisa

doi:10.3847/1538-4357/aad27e

Cited by 26 publications

(31 citation statements)

References 34 publications

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“…The first high-resolution images of the quiet Sun in the millimeter range were obtained by White et al (2006) and Loukitcheva et al (2006) who used the Berkeley-Illinois-Maryland Association Array (BIMA) to obtain ∼ 10 ′′ resolution. With the advent of ALMA a new generation of high-resolution millimeterwavelength images has been forming (e.g., Bastian et al, 2017;Shimojo et al, 2017a,b;Nindos et al, 2018;Yokoyama et al, 2018;Jafarzadeh et al, 2019;Loukitcheva et al, 2019;Molnar et al, 2019;Patsourakos et al, 2020;Wedemeyer et al, 2020) and an example is presented in Figure 2. The figure indicates that the chromospheric network, delineated in the AIA 1,600 Å image, is the dominant structure in the radio images.…”

Section: Imaging Observations Of the Non-flaring Sunmentioning

confidence: 99%

Incoherent Solar Radio Emission

Nindos

2020

Front. Astron. Space Sci.

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Incoherent solar radio radiation comes from the free-free, gyroresonance, and gyrosynchrotron emission mechanisms. Free-free is primarily produced from Coulomb collisions between thermal electrons and ions. Gyroresonance and gyrosynchrotron result from the acceleration of low-energy electrons and mildly relativistic electrons, respectively, in the presence of a magnetic field. In the non-flaring Sun, free-free is the dominant emission mechanism with the exception of regions of strong magnetic fields which emit gyroresonance at microwaves. Due to its ubiquitous presence, free-free emission can be used to probe the non-flaring solar atmosphere above temperature minimum. Gyroresonance opacity depends strongly on the magnetic field strength and orientation; hence it provides a unique tool for the estimation of coronal magnetic fields. Gyrosynchrotron is the primary emission mechanism in flares at frequencies higher than 1-2 GHz and depends on the properties of both the magnetic field and the accelerated electrons, as well as the properties of the ambient plasma. In this paper we discuss in detail the above mechanisms and their diagnostic potential.

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Section: Imaging Observations Of the Non-flaring Sunmentioning

confidence: 99%

Incoherent Solar Radio Emission

Nindos

2020

Front. Astron. Space Sci.

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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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“…Recent studies have shown the potential of ALMA to examine distinct phenomena both in quiet and active regions [31][32][33][34][35][36][37][38][39][40]. In particular, Eklund et al [41] found signatures of shock-wave events in Band 3 (2.8-3.3 mm) observations from December 2016, coming to the conclusion that there are numerous small-scale dynamic structures with lifetimes of 43-360 s present in the ALMA field of view (FOV), with excess temperatures of more than 400 K and a correlation between their occurrence and the magnetic field strength.…”

Section: Introductionmentioning

confidence: 99%

High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array

Gómez

Jafarzadeh

Wedemeyer

et al. 2020

Phil. Trans. R. Soc. A.

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We report detection of oscillations in brightness temperature, size and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with high temporal resolution (i.e. 2 s cadence) with the Atacama large millimetre/ submillimetre array (ALMA) in Band 3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, 90 ± 22 s, 110 ± 12 s and 66 ± 23 s, respectively. We find anti-correlations between perturbations in brightness, temperature and size of the three features, which suggest the presence of fast sausage-mode waves in these small structures. In addition, the detection of transverse oscillations (although with a larger uncertainty) may also suggest the presence of Alfvénic oscillations which are likely representative of kink waves. This work demonstrates the diagnostic potential of high-cadence observations with ALMA for detecting high-frequency magnetohydrodynamic waves in the solar chromosphere. Such waves can potentially channel a vast amount of energy into the outer atmosphere of the Sun. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

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ALMA Observations of the Solar Chromosphere on the Polar Limb

Cited by 26 publications

References 34 publications

Incoherent Solar Radio Emission

Incoherent Solar Radio Emission

The Sun at millimeter wavelengths

High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array

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