Convective Characteristics over the East Pacific and Southwest Amazon Regions:

A Radar Perspective

Luis Gustavo Paiva Pereira and Steven A. Rutledge

Department of Atmospheric Science - Colorado State University – Fort Collins, CO

This research focuses in evaluating the differences in convective characteristics over two tropical regions: the East Pacific warm-pool and the southwest Amazon. Convection is examined using radar data collected during the EPIC (Eastern Pacific Investigation of Climate Processes in the Coupled Ocean-Atmosphere System) and TRMM-LBA (Tropical Rainfall Measuring Mission - Large Scale Biosphere-Atmosphere in Amazonia) field experiments.

In both tropical regions, two distinct wind regimes were observed and defined by the direction of the low-level flow. During TRMM-LBA (EPIC) the low-level flow switched back and forth from easterly (northerly) to westerly (southerly) flow, with periods on the order of five to fourteen (two to five) days. Previous studies have shown that the direction of the low-level flow over the EPIC domain is associated with the regular passage of easterly waves, whereas the low-level flow in the TRMM-LBA domain is associated with the passage of baroclinic waves over the subtropical regions of Brazil.

The variability of the convective characteristics is evaluated in each region as a function of time of day and wind circulation. Some of the features used to evaluate the convective characteristics include convective fraction, reflectivity profiles and fraction of convective areas producing warm rain. The results presented in this study show that the easterly (LBA) and northerly wind regimes (EPIC) more frequently featured stronger convection: greater reflectivities and convective fractions, deeper convective cores and smaller fractions of warm-rain-producing areas. The results indicated that convection initiates in the morning and peaks in the afternoon over the TRMM-LBA domain, whereas in the EPIC region the convection initiates after sunset and peaks near sunrise. Wind regime variations were observed to be more intense in the TRMM-LBA region.