Convective systems in contrasting regimes during TRMM-LBA in Rondonia, Brazil

The Tropical Rainfall Measuring Mission - Large Scale Biosphere-Atmosphere Experiment in Amazonia (TRMM-LBA) was conducted near Ji Parana, Rondonia, Brazil during the 1999 Amazonian wet season (Jan-Feb). TRMM-LBA provided detailed observations of precipitating systems from surface and aircraft instrumentation. The surface-based platforms included two scanning Doppler radars (the NASA TOGA C-band radar and the NCAR SPOL S-band dual-polarization radar) which collected continuous dual-Doppler measurements of precipitating convection. Soundings as often as every three hours were launched at a site near the TOGA radar.

Areal coverage time series of low-level reflectivity from the TOGA radar suggest distinct regimes of convection. These regimes may be characterized by the direction of system propagation and by the ratio of light to heavy precipitation areal coverage. Systems which move from the east have a higher ratio of heavy rainfall to light rainfall. The east-moving systems contain deeper convective cells on average than the west-moving systems. The east versus west moving systems occur in alternating periods which vary in time but are on average about 15 days duration. The east vs. west moving systems are reminiscent of differences in break vs. monsoon systems in northern Australia.

Examples from both regimes of the evolution of convective systems and the environment in which they form will be presented. Reflectivity and radial velocity data provide a view of the evolution of precipitation structure and mesoscale flow features in convective systems in each regime. Sounding data are used to compare convective available potential energy, stability, dry air layers, and wind hodographs between east vs. west moving systems.