CONVECTION IN TOGA COARE - HORIZONTAL SCALE, MORPHOLOGY, AND RAINFALLPRODUCTION

The occurrence frequency and rainfall production of mesoscale convecti ve systems (MCSs) relative to smaller groups of convective clouds over the tropical oceans is not well known. Eighty days of shipboard radar data collected during the recent Tropical Ocean Global Atmosphere Cou pled Ocean-Atmosphere Response Experiment (TOGA COARE) were used to pr ovide a detailed view of convection in the western Pacific warm pool, a region of global climatological significance. The aim of this study was to document the frequency of occurrence, rainfall production, and depth of convection observed during TOGA COARE within a simple and mea ningful framework of convective horizontal organization. Organization was characterized in terms of the horizontal scale and morphology of c onvective systems. Precipitation events were defined based on whether they attained the length scale of an MCS, and on whether convection wa s organized into lines. About four-fifths of rainfall during COARE was associated with MCS-scale squall lines. These occurred in a variety o f wind regimes but tended to be most common prior to low-level westerl y wind maxima. Systems of isolated cells produced 12% of all COARE rai nfall and were observed during periods of both very weak and very stro ng low-level winds. These two modes occurred about equally as often, a nd together they accounted for about 90% of observed convection. Cloud height populations associated with MCS organization were distinct fro m sub-MCS-scale cloud systems, with more rainfall from shallower cloud s for sub-MCS convection. The distribution of total rainfall by cloud height for COARE was interpreted as a superposition of rainfall-cloud height distributions from each mode of organization. These results rai se the possibility that isolated cell periods may represent a distinct , nonnegligible heat source in the large-scale heat budget when compar ed to the dominant MCS-scale systems.