A Simple Model for Stratocumulus to Shallow Cumulus Cloud Transitions

Abstract

t is shown that essential features of stratocumulus to shallow cumulus cloud transitions can be represented by a simple stochastic model constructed from an ensemble of transitions, each of which depends on the amount of surface latent heat flux relative to initial cloud-top longwave net radiative flux. In its essence the simple model establishes a causal relation between the increase of sea surface temperature (SST) and the decrease in cloud fraction (CF) along the trade winds. The mean and variance of SST are taken from observations. Model predictions are compared with observations of CF along Lagrangian trajectories in four eastern subtropical ocean regions. The model reproduces well the decrease in mean CF and the peak in CF spread.