Solar polarization observations at 3 and 13 mm
by J. Kallunki and M. Tornikoski

2020-04-28 221 views

Microwave solar polarization observations give us information about the magnetic field of the solar atmosphere. They are important for understanding the various solar activity phenomena and emission mechanisms related to them. Polarization properties of solar active regions have been studied previously mainly at lower radio frequencies. Here we present solar radio polarization observations that were made at Aalto University Metsähovi Radio Observatory (MRO) in Finland with the 13.7-metre radio telescope, […]

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

2020-02-18 415 views

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

2019-10-01 393 views

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 […]

Large area solar flare ribbons as the model to explain puzzling millimeter emission
by G.G. Motorina et al.*

2019-03-12 409 views

Solar flares are sudden explosive processes, that convert the energy of the magnetic field into the kinetic energy of electrons and ions. Since the beginning of the century, millimeter observations of solar flares became routinely possible at a few frequencies with limited spatial resolution (see Kaufmann 2012, as a review). One of the most puzzling aspects of the observations at millimeter wavelengths (200-400 GHz) is the presence, in some flares, […]

Temperature constraints from inversions of synthetic solar optical, UV and radio spectra
by J. M. da Silva Santos et al*

2019-02-12 334 views

While the solar chromosphere has been routinely observed in high-resolution from ground-based optical telescopes such as the Swedish Solar Telescope (SST), and more recently in the UV from space-borne telescopes such as the Interface Region Imaging Spectrograph (IRIS), radio observations lag behind despite their great potential. Distinctly from photospheric lines, most chromospheric diagnostics such as Ca II 854.2 nm and Mg II h and k form under non-LTE conditions, therefore […]

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

2018-11-27 494 views

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 […]

Topical issue “Solar radio physics from the chromosphere to near Earth” published
by E.P Kontar and A. Nindos

2018-06-26 588 views

The 2016 CESRA workshop ( had a special emphasis on the complementarity of current and future space-based observations with ground-based radio observations. It was the place to discuss the new exciting science opportunities that arise from radio instruments such as the Atacama Large Millimeter/submillimeter Array (ALMA), the Expanded Owens Valley Solar Array (EOVSA), the Expanded Very Large Array (EVLA), the Low Frequency array (LOFAR), the Mingantu Spectral Radioheliograph (MUSER), and […]

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

2018-02-20 780 views

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 […]

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