Extreme convection in subtropical South America: TRMM observations and high-resolution modeling

Extreme convection tends to form in the vicinity of mountain ranges, and the Andes in subtropical South America help spawn some of the most intense convection in the world. Measurements from the TRMM satellite have allowed for detailed analysis of extreme weather patterns in remote regions of the world, such as subtropical South America. An investigation of the most intense storms for 11 years of TRMM Precipitation Radar (PR) data has shown a tendency for squall lines to initiate and develop in this region. The synoptic environment and mechanisms leading to extreme convection and MCSs in subtropical South America are similar to those found in other regions of the world, including the United States. The mesoscale organizational structure of storms in subtropical South America and the U.S. are markedly similar. However, the topographical influence on the convective initiation and maintenance of the MCSs is unique to South America, where the Andes and related topography focus deep convection in a narrow region.

In a previous study, we examined the storm evolution by making use of the time continuity of the GOES infrared satellite data and NCEP/NCAR reanalysis. However, information about the underlying dynamics could not be determined from the data alone. Therefore, we have conducted numerical simulations with the NCAR Weather Research and Forecasting (WRF) Model to extend the analysis and provide an objective dynamical evaluation of storm initiation mechanisms, which include a capping inversion in the lee of the Andes, and mesoscale organization. We simulated two representative cases with triple-nested domains. The simulated mesoscale systems closely resemble the storm structures seen by the TRMM satellite as well as the overall shape and character of the storms shown in the GOES satellite data. Results from these simulations will be presented at the conference including the role of small scale topographic features, subsidence in the lee of the Andes, and sensitivity to microphysics.