# ALMA as the ideal probe of the solar chromosphere

## TL;DR

This paper highlights ALMA's potential to advance understanding of the solar chromosphere by providing high-resolution millimeter observations that can detect dynamic processes and distinguish between competing models.

## Contribution

It demonstrates the suitability of ALMA for probing the solar chromosphere's dynamics through millimeter wavelength observations, supported by dynamic modeling and initial observational results.

## Key findings

- Millimeter emission is highly sensitive to chromospheric dynamics.
- Initial BIMA observations show significant oscillations in the quiet Sun.
- High-resolution ALMA observations are needed for detailed analysis.

## Abstract

The very nature of the solar chromosphere, its structuring and dynamics, remains far from being properly understood, in spite of intensive research. Here we point out the potential of chromospheric observations at millimeter wavelengths to resolve this long-standing problem. Computations carried out with a sophisticated dynamic model of the solar chromosphere due to Carlsson and Stein demonstrate that millimeter emission is extremely sensitive to dynamic processes in the chromosphere and the appropriate wavelengths to look for dynamic signatures are in the range 0.8-5.0 mm. The model also suggests that high resolution observations at mm wavelengths, as will be provided by ALMA, will have the unique property of reacting to both the hot and the cool gas, and thus will have the potential of distinguishing between rival models of the solar atmosphere. Thus, initial results obtained from the observations of the quiet Sun at 3.5 mm with the BIMA array (resolution of 12 arcsec) reveal significant oscillations with amplitudes of 50-150 K and frequencies of 1.5-8 mHz with a tendency toward short-period oscillations in internetwork and longer periods in network regions. However higher spatial resolution, such as that provided by ALMA, is required for a clean separation between the features within the solar atmosphere and for an adequate comparison with the output of the comprehensive dynamic simulations.