Evolution of mesoscale convective systems in contrasting large scale regimes from radar and infrared satellite data during the TRMM-LBA field campaign in RondÔnia, Brazil (Formerly paper 5B.6)

Distinct low level wind regimes were observed during the TRMM-LBA field campaign in southwest Amazonia (Rondonia, Brazil) during Jan.-Feb. 1999. Periods of northwesterly winds centered at 850mb, associated with the monsoon trough, were separated by periods of low level easterly winds at the sounding location. A preliminary analysis of radar reflectivity data from surface radar observations suggests that the organization of mesoscale convective systems was distinct between westerly and easterly wind regimes. In this study, surface-based radar reflectivity data and infrared (IR) geostationary satellite data are used to characterize two mesoscale convective systems (MCSs), one from each of these regimes. If available, preliminary results from dual-Doppler vertical motion retrievals will be discussed for these cases.

MCSs observed during the easterly regime were typified by deep, electrified, afternoon squall lines which moved from east to west. An easterly regime system on 26 January 1999 propagated into the dual-Doppler radar network during its mature to decaying stage. The evolution of this system will be described by time series of convective and stratiform rain intensity and areal coverage from radar reflectivity data. IR data will be used to track the system origin and decay from outside of the radar network. Correlations between cloud top brightness temperature and the low level radar reflectivity fields show the evolving relationship between the surface precipitation pattern and the location of cold anvil clouds.

MCSs with a more dominant stratiform rain component and little lightning activity were typical of the westerly regime. A nocturnal system which occurred on 2 February 1999 will be discussed, using radar reflectivity and IR satellite data as described above. This system was characterized by widespread stratiform precipitation, weak embedded convective cells, and shallow echo tops of about 7 km. Cloud top temperatures were much warmer than the easterly systems, illustrating significant precipitation areal coverage from relatively warm clouds. Such a relationship may be typical of monsoon systems.