Representing the oscillatory changes in cloud field properties as a function of cloud size distribution

Marine boundary-layer clouds have been observed to evolve periodically; the cloud field can go through a phase where large, precipitating clouds dominate, followed by a phase where the cloud formation is suppressed by evaporative cooling. We examine the organization and evolution of the marine boundary-layer cloud field, modelled by a high-resolution, large-eddy simulation of a turbulent atmosphere.

Individual cloud regions are isolated and probability distributions of individual cloud properties are used to examine the efficacy of cloud size distribution to represent the strength of convective activities across the observed cloud field. Probabilistic statistical methods based on Bayesian inference are employed to study how the time-series of cloud field properties, such as the cloud size distribution, are correlated to a number of cloud properties, such as individual cloud mass flux. We show that these properties, especially individual cloud mass flux and precipitation, are strongly correlated with the oscillatory changes in the cloud size distribution. The correlations between the distribution of cloud sizes and the strength of turbulent mixing, expressed in terms of direct entrainment and dilution rates, are also examined. These findings have implications for a better representation of convective dynamics in numerical modelling of the atmosphere and a better interpretation of observational data from satellite and in-situ measurements.