Lightning, thermodynamic and hydrological comparison of the two tropical continental chimneys

The two major tropical continental zones of active convection-Africa and South America-are compared from the standpoint of lightning activity, rainfall, thermodynamics, hydrology and aerosol-influenced cloud microphysics. Comparisons of temperature, diurnal temperature range, insolation, Bowen ratio, response to semiannual forcing, inundation fraction, boundary layer relative humidity and associated cloud base height are all self consistent in showing a more continental surface for Africa than South America. These surface characteristics are shown to play a major role in the substantial contrast (annual ratio 2.8) in lightning flash rate density between the two major drainage basins in these two continents. The Congo is slightly hotter and slightly drier than the Amazon, with a contrast in wet bulb potential temperature and convective available potential energy that is difficult to resolve given limitations in the observations. Aerosol effects in cloud microphysics may be needed to account for quantitative shortfalls in explanations for lightning and rainfall on the basis of thermodynamics alone. Additional information about aerosols is needed to clarify their role. The clear African dominance in lightning and Schumann resonance intensity presents a paradox for the behavior of the 'dc'global electrical circuit that is resolvable by dominance of electrified shower clouds in South America, as hypothesized by Wilson. (C) 2004 Elsevier Ltd. All rights reserved.