Effects of Mesoscale Convergence on Cloud Convection

Abstract

A two-dimensional time-dependent cloud model was used in this research to investigate the effects of mesoscale convergence on cloud convection. A Klemp and Wilhelmson type boundary condition was tested which allows inflow and outflow through the lateral boundary and also lets gravity waves pass out through the boundaries with minimal reflection. A relatively stable and easy method of superimposing a mesoscale convergence field was also introduced in this study. The main idea of this superposition is to decompose the velocity into mesoscale and cloud-scale velocities. The cloud-scale velocity is governed by the cloud convection, while the mesoscale velocity is governed by the mesoscale variable. Two types of atmospheric soundings were run in this model. The first type is an unstable sounding and the second type is conditionally unstable with a low-level inversion. The results show that convergence weakens the temperature inversion and leads to strong convection in one case. Fewer, broader and more vigorous clouds were evident in another mesoscale convergence case.