Diurnal evolution of non-precipitating marine stratocumuli in an LES ensemble

Abstract. We explore the impacts of the diurnal cycle, free-tropospheric (FT) humidity values, and interactive surface fluxes on the cloud system evolution of non-precipitating marine stratocumuli based on a large ensemble of large-eddy simulations. Cases are separated into three categories based on their degree of decoupling and cloud liquid water path (LWP_c). A new budget analysis method is proposed to analyze the evolution of LWP_c under both coupled and decoupled conditions. More coupled clouds start with relatively low LWP_c and cloud fraction (f_c) but experience the least decrease in LWP_c and f_c during the daytime. More decoupled clouds undergo greater daytime reduction in LWP_c and f_c, especially those with higher LWP_c at sunrise because they suffer from faster weakening of a net radiative cooling. During the nighttime, a positive correlation between FT humidity and LWP_c emerges, consistent with higher FT humidity reducing both radiative cooling and the humidity jump, both of which reduce entrainment and increase LWP_c. The time rate of change in the LWP_c is more likely to be negative for higher LWP_c and greater inversion base height (z_i), conditions under which entrainment dominates as turbulence develops. In the morning, the rate of the LWP_c reduction depends on the LWP_c at sunrise, z_i, and the degree of decoupling, with distinct contributions from subsidence and radiation. Under well-mixed conditions, it takes about 10 h for the surface fluxes to offset 15 % of the changes in entrainment warming and drying, assuming no changes in transfer coefficients or surface wind speed.