Methane volume mixing ratio in the atmosphere of Neptune retrieved by different observations and models. The dotted line represents the liquid saturated CH₄ vmr calculated from Lindal (1992) temperature profile and the dashed line is the ice saturated CH₄ vmr. The CH₄ vmr profile used in our model is Lellouch et al. (2015) between 1500 and 100 hPa from and Moses et al. (2018) above 100 hPa level. Below the 1500 hPa, the CH₄ vmr value from Irwin et al. (2019) is assumed.