CO(J=3-2) / CO(J=2-1) Intensity Ratio emitted from the surface of a PDR as a function of the cloud density n and the FUV flux incident on the cloud G₀. The models in the wk2020 ModelSet are based on Kaufman et al. 2006 , Wolfire et al. 2010, and Neufeld & Wolfire 2016. They use these parameters. More details are in the FITS headers.