Turbulent Exchange of CO2 ${\text{CO}}_{2}$ in the Lower Tropical Troposphere Across Clear‐to‐Cloudy Conditions

Abstract This study investigates the roles of clear air entrainment and shallow cloud ventilation, alongside rainforest ‐assimilation, in the turbulent exchange of within the lower tropical troposphere under clear‐to‐cloudy conditions. Constrained by comprehensive observations from the CloudRoots‐Amazon22 campaign, spanning leaf stomatal to upper atmosphere, we design and evaluate a representative shallow convective numerical experiment with the turbulence‐resolving Dutch Atmospheric Large Eddy Simulation model, incorporating a bulk rainforest representation. We assess contributions from the rainforest, clouds, and environment through the vertically integrated, domain‐averaged budget by comparing simulations with and without the dynamic effects of clouds. Our findings reveal three distinct diurnal regimes named: entrainment‐diluting, cloud‐ventilation‐and‐entrainment, and ‐assimilation. Shallow convective clouds (23%), clear air entrainment (21%), and rainforest ‐assimilation (56%) collectively influence the diurnal evolution and vertical exchange of within the clear‐to‐cloudy boundary layer, with their relative importance varying per diurnal regime. In the absence of clouds, ventilation ceases and exchange is driven solely by entrainment and ‐assimilation, resulting in a 20%–25% reduction in mixing effectiveness. In the vertical, shallow clouds ventilate to heights reaching twice the boundary layer depth, significantly affecting the vertical distribution until late afternoon. Analysis of the correlation between and O shows that shallow convective clouds organize the turbulent exchange at shallow cloud‐scales, shaping a vertical pattern of negative to positive ‐O correlation from the roughness sublayer into the cloud layer. These findings highlight key processes crucial for accurately representing the lower tropical tropospheric budget across clear‐to‐cloudy conditions.