EFFECTS OF PERSISTENT, MIDLATITUDE MESOSCALE REGIONS OF CONVECTION ONTHE LARGE-SCALE ENVIRONMENT DURING THE WARM-SEASON

Over a 2 1/2-day period beginning 0000 UTC 11 May 1982, 15 mesoscale c onvective systems (MCSs) developed and moved eastward across the moist axis located over the southern plains of the United States. While the 6-18-h lifetimes of each of these individual MCSs are not sufficientl y long to influence the large-scale environment greatly, it is possibl e that the cumulative effects of the entire group of MCSs can produce significant changes in the large-scale flow patterns. This hypothesis is investigated using output from two runs of a sophisticated mesoscal e model. One run includes the effects of convection, and the other doe s not. Results indicate that in low levels, the inflow of warm, moist air into the convective region is increased when convection is allowed in the model, enhancing the likelihood that convection will continue and thereby acting as a positive feedback mechanism. In upper levels, the convection acts as a Rossby wave source region and produces signif icant upper-level perturbations that cover at least a 50 degrees longi tude spread. Convective effects also influence cyclogenesis since the MCSs strengthen the low-level baroclinicity and modify the phase relat ionship between pressure and thermal waves in the midlevels. Thus, it is clear that the effects of a persistent, mesoscale region of convect ion on the large-scale environment are substantial.