TRMM Observations of Intraseasonal Variability in Convective Regimes over the Amazon

Abstract

This study utilizes the Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar (PR), lightning imaging sensor (LIS), and passive microwave imager (TMI) data together with ground-based lightning data to investigate the vertical structure, lightning, and rainfall characteristics of Amazonian and subtropical South American convection for three separate wet seasons. These characteristics are partitioned as a function of 850-mb zonal wind direction, motivated by observations collected during the 6-week TRMM?Large-scale Biosphere?Atmosphere Experiment in Amazonia (LBA) field campaign. The TRMM?LBA field campaign observations suggest that systematic variations in Amazonian convective vertical structure, lightning, and rainfall are all linked to bimodal variations in the low-level zonal wind (e.g., easterly and westerly regimes). The more spatially and temporally comprehensive TRMM dataset used in this study extends the TRMM?LBA observations by examining regime variability in Amazonian and South American convective structure over a continental-scale domain. On a continental scale, patterns of east and west regime 850?700-mb winds combined with LIS lightning flash densities suggest the presence of synoptic-scale controls [e.g., intrusion of extratropical frontal systems and interaction with the South Atlantic Convergence Zone (SACZ)] on regional-scale variability in convective vertical structure. TRMM PR, TMI, and ground-based lightning data suggest that regional variability in wet-season convective structure is most evident over the southern Amazon, Mato Grosso, Altiplano, southern Brazil, and eastern coastal regions of central and southern South America. Convective vertical structure, convective rainfall rates, and lightning activity are all more pronounced during easterly (westerly) regimes over the southern Amazon and Mato Grosso (Altiplano, and southern Brazil). Importantly, when considered with case study results from TRMM?LBA, the systematic differences in convective structure that occur as a function of regime suggest that associated regime differences may exist in the vertical distribution of diabatic heating. Hence the discrimination of convective vertical structure ?regimes? over parts of the Amazon and vicinity based on a resolved variable such as the 850?700-mb zonal wind direction, while far from being perfect, may have important applications to the problems of cumulus parameterization, rainfall estimation, and retrievals of latent heating over the Amazon.