Small Collisions, Big Impact: The Sensitivity of Atmospheric Temperatures to Collision-Induced Absorption

Abstract

Collision-induced absorption (CIA) data are relevant to determining atmospheric temperatures and, in turn, the habitability of a diverse set of planetary atmospheres. However, these data remain sparse across broad wavelength and temperature ranges. Nevertheless, multiple, sometimes disagreeing, sources of experimental and theoretical data can be available for the same CIA pair. In this paper, we assess the impact of these varying sources on atmospheric temperatures and the limitations that the available data coverage can introduce. In order to inform future measurements and calculations, we test additional cases with extrapolated wavelength and temperature ranges. We first introduce a measure of the importance of CIA opacities depending on pressure and temperature by calculating the Rosseland mean with and without each CIA pair's contribution. Secondly, we employ each CIA source in a radiative transfer model of idealised atmospheres which maximise the effect of the CIA pair of interest. Our findings highlight the uncertainties related to the current data. Temperature differences between CIA data sources range from $\sim$10\,K when sources overlap in wavelength and temperature coverage to >100\,K when spectral gaps or temperature limits differ. Spectral windows or narrow temperature coverage can also hinder the model's convergence of the temperature profile. This work aims to provide guidance on the selection of CIA opacity datasets for atmospheric modelling and to identify the wavelength and temperature regimes in which further laboratory measurements and theoretical calculations are most urgently needed. We publish all our findings in detail in the form of an accessible website.