Raindrop Size Distribution and Radar Parameters in Coastal Tropical Rain Systems of Northeastern Brazil

• Published in: Journal of applied meteorology and climatology 2012-11, Vol.51 (11), p.1960-1970
• Main Authors: Tenório, Ricardo Sarmento, da Silva Moraes, Marcia Cristina, Sauvageot, Henri
• Format: Article
• Language: English
• Subjects: Atmospheric and Oceanic Physics; Coastal zone; Coasts; Coefficient of variation; Datasets; Earth, ocean, space; Exact sciences and technology; External geophysics; Geophysics. Techniques, methods, instrumentation and models; Land; Meteorology; Oceans; Physics; Precipitation; Radar; Rain; Raindrops; Rainfall; Reflectance; Size distribution; Storms; Water in the atmosphere (humidity, clouds, evaporation, precipitation)
• ISSN: 1558-8424; 1558-8432
• DOI: 10.1175/JAMC-D-11-0121.1

A dataset on raindrop size distribution (DSD) gathered in a coastal site of the Alagoas state in northeastern Brazil is used to analyze some differences between continental and maritime rainfall parameters. The dataset is divided into two subsets. One is composed of rainfall systems coming from the continent and moving eastward (i.e., offshore), representing the continental subset. The other is composed of rainfall systems that developed over the sea and are moving westward (i.e., inshore), representing the maritime subset. The mean conditional rain rate (i.e., for rain rateR> 0) is found to be higher for maritime (4.6 mm h−1) than for continental (3.2 mm h−1) conditions. The coefficient of variation of the conditional rain rate is lower for the maritime (1.75) than for the continental (2.25) subset. The continental and maritime DSDs display significant differences. For drop diameterDsmaller than about 2 mm, the number of drops is higher for maritime rain than for continental rain. This reverses forD> 2 mm, in such a way that radar reflectivity factorZfor the maritime case is lower than for the continental case at the same rain rate. These results show that, to estimate precipitation by radar in the coastal area of northeastern Brazil, coefficients of theZ–Rrelation need to be adapted to the direction of motion of the rain-bearing system, inshore or offshore.