The quiet Sun at mm Wavelengths as Seen by ALMA

TL;DR

This paper reviews initial ALMA observations of the quiet solar chromosphere at millimeter wavelengths, highlighting temperature measurements, comparison with models, and future prospects for high-resolution solar studies.

Contribution

It provides a comprehensive overview of early ALMA results on the quiet Sun, emphasizing new insights into chromospheric temperature structure and magnetic features.

Findings

Temperature structure consistent with empirical models

Detection of chromospheric network and spicules

Potential for advanced magnetometry with future ALMA upgrades

Abstract

Solar observations at sub-mm, mm and cm wavelengths offer a straightforward diagnostic of physical conditions in the solar atmosphere because they yield measurement of brightness temperature which, for optically thick features, equals intrinsic temperature - much unlike solar diagnostics in other spectral ranges. The Atacama Large Millimeter and sub-millimeter Array (ALMA) has therefore opened a new, hitherto underexplored, spectral window for studying the enigmatic solar chromosphere. In this review we discuss initial ALMA studies of the quiet chromosphere that used both single-dish and compact-array interferometric observing modes. We present results on the temperature structure of the chromosphere, comparison with classic empirical models of the chromosphere, and observations of the chromospheric network and spicules. Furthermore, we discuss what may be expected in the future, since the ALMA capabilities continuously expand and improve towards higher angular resolution, wavelength coverage, and polarization measurement for magnetometry.