A climatology of tropical congestus using CloudSat

Cumulus congestus clouds have long been identified as an important part of the spectrum of convective clouds in the tropics. These clouds—which range in size from growing cumulus to slightly smaller than a cumulonimbus—make important contributions to precipitation and latent heat fluxes in the tropics. Past studies have used numerical simulations and satellite observations to examine these clouds globally, although definitions of congestus vary between studies. In this study, congestus in the tropics are identified using contiguous cloud area with cloud tops between 5 and 8 km from 5 years of CloudSat reflectivity data. Alternatively, congestus clouds are defined by contiguous cloud areas with infrared brightness temperature ranging from 273 to 260 K and radar-detected surface rainfall from 14 years of Tropical Rainfall Measuring Mission (TRMM) data. Due to the resolution of CloudSat, the congestus identified using this method represent groups of congestus clouds rather than individual turrets. The regional, seasonal variations of the population of congestus are presented globally. Congestus clouds are found most frequently over the Amazon. There is a strong diurnal variation of congestus clouds over land with a peak in the early afternoon shown by TRMM. General differences are found between the properties of congestus over land and those over ocean, especially the shapes of groups of congestus over land and ocean. Ocean congestus clusters are more bell shaped, while land congestus clusters tend to have flatter sides and larger area above the freezing level. These differences have important implications in the proper representation of congestus in numerical models.