Radiative and Microphysical Characteristics of Deep Convective Systems in the Tropical Western Pacific

Abstract

The radiative and microphysical characteristics of 17 precipitating systems observed by the Tropical Rainfall Measuring Mission (TRMM) satellite over Manus, Papua New Guinea, and Nauru Island are modeled. These cases represent both deep and midlevel convection. Reflectivity data from the TRMM precipitation radar and Geostationary Meteorological Satellite infrared radiometer measurements are used to parameterize the three-dimensional cloud microphysics of each precipitating cloud system. These parameterized cloud properties are used as input for a two-stream radiative transfer model. Comparisons with measurements of broadband radiative fluxes at the top of atmosphere and the surface show agreement to within 20%. In cases in which the convective available potential energy (CAPE) is large, deep convective clouds with extended anvil decks form, containing layers of ice crystals that are too small to be detected by the TRMM radar but have a large optical thickness. This results in maximum shortwave heating and longwave cooling near cloud top at heights of 12?14 km. When CAPE is small, convective clouds extend only to midlevels (4?7 km), and there are no cloud layers below the detectability limit of the TRMM radar. Radiative heating and cooling in these cases are maximum near the freezing level. A sensitivity analysis suggests that the small ice crystals near the cloud top and larger precipitation-sized particles play equally significant roles in producing the high albedos of tropical anvil clouds. A comparison of the radiative heating profiles calculated in this study with latent heating profiles from previous studies shows that for cases of mature deep convection near local solar noon, the maximum radiative heating is 10%?30% of the magnitude of the maximum latent heating.