Link between opaque cloud properties and atmospheric dynamics in observations and simulations of current climate in the Tropics, and impact on future predictions'

Using spaceborne lidar observations and reanalyses (2008-2014), we relate the vertical wind speed at 500 hPa (⍵500), indicator of atmospheric circulation, to properties of opaque clouds (altitude and cover) and to the Cloud Radiative Effect (CRE) in the Tropics. We confront those observations with simulations by IPSL-CM6 and CESM1 climate models using early 21st century emissions. Both models overestimate the average opaque cloud cover. IPSL-CM6 puts high opaque clouds too high (+2km), especially in ascendance. CESM1 overestimates the intermediate opaque cloud cover and underestimates small and large opaque cloud covers. Both models agree that cloud properties behave differently at wind speed above (strong subsidence) or below (weak subsidence and ascendance) 20hPa/day. In future climate (2089-2095), variables affected by biases in current climate are affected by notable changes: IPSL-CM6 puts high opaque clouds even higher (+2km) while opaque cloud cover above 30% decreases and below 30% increases in CESM1. Both models predict very little change in the average net CRE in the future. Small but noticeable changes in the net CRE (in relatively strong ascendance or subsidence) can be explained by predicted changes in Copaque for both models, with changes in cloud altitude having little influence. We find that predicted changes of cloud properties can be regionally driven by dynamic or thermodynamic changes, depending on the relationship between opaque cloud altitude and ω500 in the model. Overall, most changes are due to thermodynamic changes in the relationship between cloud property and atmospheric dynamics.