# ALMA detection of dark chromospheric holes in the quiet Sun

## TL;DR

This paper reports ALMA observations of dark, cool chromospheric holes in the quiet Sun at 3 mm, revealing areas with significantly lower temperatures than surrounding regions, and compares these with UV, visible, and magnetogram data.

## Contribution

It provides the first ALMA imaging of dark chromospheric holes in the quiet Sun, highlighting ALMA's ability to detect cool chromospheric gas not visible in other wavelengths.

## Key findings

- Dark chromospheric holes with temperatures as low as 60% of the quiet Sun.
- ALMA detects cool chromospheric gas inferred from infrared CO spectra.
- Distinct dark areas are not visible in UV, visible, or magnetogram data.

## Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of a quiet-Sun region at a wavelength of 3 mm, obtained during the first solar ALMA cycle on April 27, 2017, and compare them with available chromospheric observations in the UV and visible as well as with photospheric magnetograms. ALMA images clearly reveal the presence of distinct particularly dark/cool areas in the millimeter maps having temperatures as low as 60% of the normal quiet Sun at 3 mm, which are not seen in the other data. We speculate that ALMA is sensing cool chromospheric gas, whose presence had earlier been inferred from infrared CO spectra.