Vertical profiles of tropical convection as observed by the TRMM satellite

We have utilized TRMM Precipitation Radar (PR) and Lightning Imaging Sensor (LIS) data to conduct statistical studies of the vertical structure of convection and precipitation processes over a wide variety of rainfall regimes in the global tropics. The objective of this research is to examine the variability in the mean vertical structure of convection across the tropics (which is related to latent heating), especially contrasting tropical continental and tropical oceanic regions.

Not unexpectedly, distributions of the vertical structure of PR reflectivity exhibited marked differences between tropical oceanic and tropical continental regimes. Oceanic reflectivities exhibited a marked decrease in the layer relative frequency of reflectivity values > 25-30 dBZ above the tropical freezing level, consistent with marked decreases in lightning activity over the tropical oceans. Where flash densities increased over the ocean (e.g., Atlantic ITCZ, Indian Ocean), similar increases in the frequency of reflectivity > 30-40 dBZ occurred above the 7 km level (-12 to -15 C). Over the tropical continents, reflectivity distributions were characteristically bimodal in height for reflectivity values exceeding 30 dBZ, suggesting the presence of both deep and shallow cloud populations. The deep, more intense sub-population of clouds (e.g., 30 dBZ above the 7 km level) comprised less than 5% of the sample, yet this sub-population was likely responsible for a significant fraction of the lightning observed over tropical continents. One question that remains to be answered is: What fraction of the total rainfall (and hence latent heating) is this deep sub-population responsible for?

Interestingly, the interior tropical continental region of Amazonia exhibited a reflectivity distribution during the wet season that more strongly resembled distributions observed over the tropical oceans. This observation is consistent with observed relative reductions in lightning activity during the wet season over the Amazon.