The Behavior of Surface Wind and Thermodynamic Fields in the Presence of Deep Convection.

Surface wind measurements taken in 1973 and 1975 in fine-mesh networks in Florida and in Illinois in 1979 are used to calculate surface divergence on the convective scale. The behavior of convective scale convergence fields is shown to be similar in Florida and Illinois. Analysis of profiles of network divergence and subsequent rainfall rates shows the value of such measurements in short-term forecasting of convective rainfall. Comparison of the convective-scale mass transports in Florida, with the Florida peninsular scale forcing reveals a relationship between the two. After the initiation of a convective scale feedback mechanism by the peninsular scale forcing, downdraft induced convergence maintains and intensifies the convective-scale activity long after the peninsular scale forcing has passed its peak. A feedback mechanism between the larger and convective scale is thus established. The decline in the efficiency of the convective scale feedback mechanism is related to the rate of change in the peninsular scale forcing. The evolution of the convective activity from a condition of weak convection to a condition of deep convection is shown to depend upon the amount of moisture mixed up into the lower cloud layer by the shallower convection. A composite Florida storm is used to show that the diurnal convective process is a very efficient mechanism in the vertical mixing of water vapor, and a relatively inefficient mechanism in production of rainfall.