With the roll-out of solar observing capabilities in 2016, the Atacama Large mm and sub-mm Array (ALMA) has been regularly observing the Sun with unprecedented spatial (~1") and temporal resolution (1s) in this wavelength range. Observations with previous instruments were sporadic and of much lower resolution, so that the mm range is largely unexplored. Moreover, radio observations offer an important advantage over observations in the optical and Extreme Ultraviolet ranges, in that the intensity of the radiation is linked in a simple way to the temperature of the emitting region,thus providing direct access to important information on the structure of the solar atmosphere, the chromosphere in this case.
So far, several works describing ALMA solar observations have been published, covering a variety of subjects, such as the structure of the quiet sun and the chromospheric network, spicules beyond the solar limb, comparison of observations with models of the low chromosphere and with radiative MHD models, weak transient phenomena and oscillations, active region plages and sunspots. The current level of solar activity has not permitted the observation of more energetic phenomena. Moreover the flare observing mode is under preparation and has not been commissioned yet. Still, there are important open theoretical issues on the mm radiation of flares. The modification of ALMA for solar observations was not a trivial issue and several instrumental aspects remain to be resolved.
The goal of this Research Topic is to make an assessment of what we have learned so far from ALMA observations of the Sun and thus put in perspective ALMA’s contribution to our understanding of the physical processes in the solar atmosphere while, at the same time, serve as a guide to future work. An additional goal is to identify observational/computational aspects that need to be addressed and thus help to improve the quality and value of the observations. To this end it will include both review articles and original works.
With the roll-out of solar observing capabilities in 2016, the Atacama Large mm and sub-mm Array (ALMA) has been regularly observing the Sun with unprecedented spatial (~1") and temporal resolution (1s) in this wavelength range. Observations with previous instruments were sporadic and of much lower resolution, so that the mm range is largely unexplored. Moreover, radio observations offer an important advantage over observations in the optical and Extreme Ultraviolet ranges, in that the intensity of the radiation is linked in a simple way to the temperature of the emitting region,thus providing direct access to important information on the structure of the solar atmosphere, the chromosphere in this case.
So far, several works describing ALMA solar observations have been published, covering a variety of subjects, such as the structure of the quiet sun and the chromospheric network, spicules beyond the solar limb, comparison of observations with models of the low chromosphere and with radiative MHD models, weak transient phenomena and oscillations, active region plages and sunspots. The current level of solar activity has not permitted the observation of more energetic phenomena. Moreover the flare observing mode is under preparation and has not been commissioned yet. Still, there are important open theoretical issues on the mm radiation of flares. The modification of ALMA for solar observations was not a trivial issue and several instrumental aspects remain to be resolved.
The goal of this Research Topic is to make an assessment of what we have learned so far from ALMA observations of the Sun and thus put in perspective ALMA’s contribution to our understanding of the physical processes in the solar atmosphere while, at the same time, serve as a guide to future work. An additional goal is to identify observational/computational aspects that need to be addressed and thus help to improve the quality and value of the observations. To this end it will include both review articles and original works.
