32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Thursday, 7 August 2003
A Radar Perspective on the Variability of Tropical Convection Characteristics over the Southwest Amazon and East Pacific Regions
L. Gustavo Paiva Pereira, Colorado State University, Ft. Collins, CO; and S. A. Rutledge
Poster PDF (34.8 kB)
The focus of this research is to study tropical convection characteristics in the southwestern Amazon and eastern Pacific warm-pool regions. Convection is examined using radar data collected during two tropical field experiments: TRMM-LBA (Tropical Rainfall Measuring Mission - Large Scale Biosphere-Atmosphere in Amazonia) and EPIC (Eastern Pacific Investigation of Climate Processes in the Coupled Ocean-Atmosphere System).

In the TRMM-LBA domain, two distinct wind regimes were observed defined by the direction of the low-level flow. During TRMM-LBA the low-level flow switched back and forth from easterly to westerly flow, with periods on the order of five to fourteen days. In the east Pacific, convection was modulated by the regular passage of easterly waves. Herein we define northerly flow in advance of the wave's trough and southerly flow following the wave's trough.

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 characteristics of convection include convective area, convective fraction, reflectivity profiles, rain rates, warm rain statistics and ice fraction. The results presented in this study show that the easterly (LBA) and northerly wind regimes (EPIC) more frequently featured stronger convection: greater rain rates, greater reflectivities and convective fractions, deeper convective cores and smaller warm-rain-producing areas. The results also showed that the easterly regime was associated with higher ice fractions, defined as the ratio of ice mass to total mass (water and ice) found at above the freezing level and within the 30-dBZ core of a convective cloud. The diurnal cycle results indicated that convection initiates in the morning and peaks in the afternoon over the southwest portion of the Amazon, whereas in the east Pacific the convection initiates after sunset and peaks just before sunrise. Variations associated with wind regime were shown to be more intense in the southwest Amazon. It was also found that the east Pacific region presented larger convective areas and convective fractions than the southwest portion of the Amazon.

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