Multisensor analysis of a squall line in the Amazon Region

Abstract

Mesoscale features of the 26 January 1999 squall line are described with measurements made during the field experiment in Rondonia, Brazil, in the wet season (WET) of the Amazon region (AMC) as part of the Large-Scale Biosphere-Atmosphere Experiment in the Amazon (LBA) and the Tropical Rainfall Measurement Mission (TRMM); henceforth referred to as the WET AMC and TRMM-LBA field experiment. The squall line moved through the experiment area from northeast to southwest with high rainfall rates in its leading edge and a poorly defined trailing stratiform precipitating area. Polarimetric and Doppler measurements from the Portable Polarimetric S-band Radar (S-POL) were analyzed in conjunction with surface and upper level data, satellite visible (VIS) and infrared (IR) measurements. These remote and local measurements of variables such as cloud spatial and temporal distribution, pressure, temperature, moisture, precipitation, and wind fields are consistent with each other as well as with similar mesoscale dynamics and thermodynamics features measured, analyzed, and modeled elsewhere [e.g., Rotunno et al., 1988; Garstang et al., 1994; Houze et al., 1990]. This tropical squall line is similar to its cousins in the midlatitudes with finer-scale structural and dynamic features such as rotation and divergence. Results suggest that the cold pool has its origins in midlevels between 400 and 600 hPa from where evaporative cooling and drop-dragging bring down colder air to the surface. The convective region is dominated by warm microphysics, while the stratiform region is dominated by cold microphysics. Moreover, both regions are characterized by monomodal drop spectra centered around 2.0 and 1.0 mm, respectively. Horizontal circulation associated with strong updrafts tends to increase cloud growth efficiency in the leading edge of the squall line. INDEX TERMS: 3314 Meteorology and Atmospheric Dynamics: Convective processes; 3329 Meteorology and Atmospheric Dynamics: Mesoscale meteorology; 3354 Meteorology and Atmospheric Dynamics: Precipitation (1854); 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3374 Meteorology and Atmospheric Dynamics: Tropical meteorology; KEYWORDS: cloud microphysics, cold pool, squall line, Amazon, remote sensing, mesoscale dynamics.