Numerical Prediction of Convectively Driven Mesoscale Pressure Systems. Part II. Mesoscale Model

Abstract A 20-level, three-dimensional, primitive equation model with 20 km horizontal resolution is used to predict the development of convectively driven mesoscale pressure systems. Systems produced by the model have life histories and structural characteristics similar to observed convectively driven meso-systems. Cooling by (parameterized) convective-scale moist downdrafts is largely responsible for meso-high formation, while warming by compensating subsidence strongly correlates with mesocyclogenesis. An hypothesis for mesocyclogenesis associated with deep convective complexes is presented. The hypothesis recognizes that certain configurations of convective activity may produce focused areas of forced subsidence warming aloft. The warming in turn causes a thickness increase aloft which creates a hydrostatic circulation favorable for evacuating mass from the subsidence column. Consequently, pressure falls beneath the layer of high-level warming. Model results supporting this hypothesis are presented.