On the Relationship Between Horizontal Moisture Convergence and Convective Cloud Formation

Abstract

A technique suggested by H.L. Kuo for parameterizing the net effect of the latent heat released by cumulus convection on large-scale flow is evaluated to determine its applicability to regions of convection in middle latitude severe storm situations. The ratio of the vertically integrated horizontal moisture divergence to the moisture required for the development of a model cloud multiplied by a given arbitrary time interval is interpreted as the amount of model cloud produced in that time interval. The model cloud is characterized by pseudo-adiabatic temperature and moisture profiles above the lifting condensation level. The technique uses computer methods and regularly available rawinsonde data. Results suggest that well-defined axes of horizontal moisture convergence generally accompany development of strong cumulus convection and that the use of a pseudo-adiabatic cloud to model the moisture requirements generally gives reasonable predicted cloud amounts. The patterns of predicted cloud formation often correlate well with observed radar patterns of strong cumulus convection. Generally, the correlation, which is based on radar data at 3-hr intervals, is good at the initial rawinsonde observation time, a little better 3 hr later, and decreases at greater time intervals between rawinsonde and radar observation time.