Turbulence scaling and buoyancy dynamics in the moist atmospheric convective boundary layer

Most previous studies of convective atmospheric boundary layer (CBL) structure and dynamics have focused on the canonical case of dry air where humidity is negligible. However, this is an oversimplification for the vast majority of realistic CBLs. Water vapor is an active scalar which influences momentum through its contribution to air density. The covariance between fluctuating water vapor and potential temperature may be either positive or negative and depends on the respective surface and entrainment fluxes of both temperature and humidity, and therefore the influence of water vapor fluctuations on moist CBL structure cannot always be neglected. In order to assess the contribution of water vapor to CBL turbulence statistics and organization, we performed a suite of 24 large eddy simulations, systematically examining the influence of the global stability parameter (-z_i/L), evaporative fraction (E_f), and humidity entrainment flux ratio (φ_wq) on turbulent structure and dynamics. We find that vertical profiles of turbulent statistics depart from classical mixed layer similarity theory, particularly under high evaporative fractions and entrainment-dominated conditions. Furthermore, we observe a regime where humidity fluctuations contribute significantly to the statistical and spatial structure of the buoyancy field, highlighting the importance of water vapor as an active scalar.