Book Description

The relationship between total area divergence and convective rainfall was examined using surface data collected during the VIN 1979 field experiment in Illinois. The mesonetwork covered an area of 2800 km 2. Total area divergence, an area-averaged quantity, can also be expressed by the line integral of the normal component of the wind around the network boundary. Total area divergence was statistically related to area rainfall based upon the criterion that a convergence event occurred anytime there was a sustained change in total area divergence of less than -1/40000s s-1 for greater than 10 minutes. The difference between initial convergence and maximum convergence was related to total area precipitation associated with the convergence. During the 33-day study, there were 106 convergence events. Forty-four of the events had rainfall, and the average was 1.53 mm per event. The correlation coefficient was -0.50. Other meteorological factors also have an influence on convergence and the production of precipitation such as middle-level moisture, stability, and low-level wind speed which improve the statistical relationships in many instances. Weighted convergence, a subset of total area divergence was also used to develop regression relationships. When compared with south Florida relationships from an earlier investigation, the Illinois results show that the correlation between convergence and rainfall has dropped a tenth in almost all cases.