### The multi-thermal chromosphere: inversions of ALMA and IRIS data by J. M. da Silva Santos et al.

2020-02-18

Observations in the ultraviolet (UV) taken with the Interface Region Imaging Spectrograph (IRIS) have shown that the bright magnetic patches, known as plage, typically feature broader and brighter MgII h and k lines, which suggests that the chromosphere above plage is hotter and denser than in the quiet-Sun (e.g., Carlsson et al. 2015). However, not all line broadening is thermal; a nonthermal broadening component of up to 10 km s$^{-1}$ […]

### Solar chromospheric temperature diagnostics: A joint Hα – ALMA analysis by K. Reardon et al

2019-10-01

There are many challenges in inferring the spatially and temporally varying temperatures of the dynamic solar chromosphere. The principal problem has been the complex formation of the spectral lines in the UV, visible, and infrared that have been the prime diagnostics to probe this region of the atmosphere. The Atacama Large Millimeter Array (ALMA), which became available for solar observations in 2016, promises to help address this issue by observing […]

### First high-resolution look at the quiet Sun with ALMA at 3 mm by A. Nindos et al.*

2018-11-27

Observations of the radio continuum at millimeter (mm) wavelengths provide a unique chromospheric diagnostic. The quiet Sun mm-wavelength emission mechanism is free-free and electrons are almost always in local thermodynamic equilibrium (e.g. Shibasaki et al. 2011 and Wedemeyer et al. 2016). The availability of mm-wavelength solar observations with ALMA can advance our knowledge on the chromosphere because of the instrument’s unique spatial resolution and sensitivity. In a previous study (Alissandrakis […]

### Solar ALMA observations: constraining the chromosphere above sunspots by M. Loukitcheva et al.*

2018-02-20

Our understanding of sunspots is far from complete despite intensive research over hundreds of years. Radiation at submillimeter and millimeter wavelengths is formed in local thermodynamic equilibrium (LTE) in the low to mid chromosphere, and its intensity depends linearly on the ambient temperature of the medium. Observations at these wavelengths thus provide important diagnostics of sunspot chromospheres (Loukitcheva et al. 2014). The largest radio telescope in the world, the Atacama […]

### Solar Prominence Modelling at ALMA Wavelengths by A. Rodger and N. Labrosse

2017-11-14

The small-scale temperature structure of prominences remains an outstanding question in solar physics. Theoretical models provide scenarios for how cool prominence plasma can be formed and maintained within the extreme conditions of the corona. However, knowledge of the detailed temperature structure of the prominence plasma and its evolution at small spatial and temporal scales is still lacking. The Atacama Large Millimeter/sub-millimeter Array (ALMA) provides a novel method for high spatial […]

### Probing the Temperature Structure of the Solar Chromosphere with ALMA by C. Alissandrakis et al.*

2017-08-01

Determining the detailed temperature structure of the solar atmosphere from observations is a basic means of constructing and testing atmospheric models. One avenue to address this problem is based on measuring the center-to-limb variation of the intensity in various spectral regions. Observations in the radio domain are particularly suited for such a task since they don’t suffer from a set of complications (e.g., departures from the ionization and local thermodynamic […]

### Solar Science with the Atacama Large Millimeter/Submillimeter Array — A New View of Our Sun by S. Wedemeyer

2017-03-14

The Atacama Large Millimeter/submillimeter Array (ALMA), which consists of 66 antennas placed on the Chajnantor plateau in the Chilean Andes, has already produced impressive results for a large range of astronomical objects. Regular observations of the Sun have been carried out for the first time in December 2016 and exciting results can be expected soon. ALMA combines high spatial, temporal, and spectral resolution with the diagnostic advantages of radiation at […]