Water and Energy Budgets of a Florida Mesoscale Convective System: A Combined Observational and Modeling Study

Abstract

Mesoscale water and energy budgets are diagnosed for a squall line during the Convection and Precipitation Electrification Experiment and combined with the results of the two-dimensional Goddard Cumulus Ensemble Model. The fine temporal and spatial resolution of cloud-scale processes contained in the model is used to reduce uncertainty in the diagnosed water budget residual and, thus, to arrive at a good estimate of storm-total rainfall. Profiles of cumulus heating (Q1) and drying (Q2) inferred from the sounding observations are in turn compared with the cloud-scale energy budget terms calculated from the model. This comparison reveals near-agreement in the magnitude and vertical distribution of the peak Q1 and Q2, and also the relative size of the heating and drying at different levels in the column. When the size of the mesoscale convective disturbance is approximately the same as the sounding observation network, it may be wrong to assume that the diagnosed vertical eddy heat transport accounts for most of the total eddy transport of moist static energy, F. The cloud model is used to resolve the relative contribution of the horizontal and vertical eddy flux convergence of heat and moisture, and thus it serves as a guide to interpreting the sounding-diagnosed total flux. The model results suggest that although the mean column vertical flux convergence is significantly larger than the column-mean horizontal flux convergence, the horizontal flux convergence does play a significant role in midlevels of the convective region. This flux convergence may be associated with a strong front-to-rear inflow that develops during the mature stage of the squall line. This study suggests that when combined with the independent results of a mesoscale cloud model, the sounding diagnostics can provide a sensitivity test for the Tropical Rainfall Measuring Mission measurements of rainfall and diabatic heating over the life cycle of an entire mesoscale convective system.