Interpreting stratocumulus climatology using Lilly's mixed-layer theory

Mixed-layer theory is used as a basis for investigating the climatology of marine stratocumulus clouds. The theory was developed by Lilly in his seminal 1968 paper. We evaluate it first using one month of data collected during the DYCOMS-II field campaign, near 120W and 30N, and then globally over the World Ocean using boundary forcings taken from the ECMWF Reanalysis (ERA40). Equilibrium boundary layer depths and liquid water paths from the mixed-layer theory are shown to match the DYCOMS-II data, on the one hand, and the broader geographic and seasonal distribution of stratocumulus clouds, on the other. We rely on this good qualitative agreement to apply the theory to more quantitatively capture important elements of the seasonal variation of stratocumulus and to explore the principal controling factors for such variations; these factors include advection, radiative forcing, lower-tropospheric stability, and divergence. The contribution of transients to temporal means is quantified through a comparison of equilibrium cloud fields generated by compositing equilibrium solutions over daily, monthly and climatological monthly cloud fields, respectively.