Grouping of clouds in a numerical cumulus convection model

Abstract

Simulations with a two-dimensional numerical model of cumulus convection with random forcing are presented. The domain size is 4 by 60km, with a grid distance of 200m. We have carried out a number of 5 h real time simulations. The results show that, if convection is deep enough, cumulus clouds tend to occur in groups. A typical cloud size is 3 km, whereas cloud groups have a diameter of about 15 km. Downdraughts play an important role in producing these groups. For shallow convections this grouping or clumping of clouds does not take place, although the flow in this case is also strongly organized (formation of stratocumulus). The factors responsible for organizing the flow are examined.