The feasibility of a dual-frequency radar system in studying the morphology of subtropical precipitation

Abstract

Investigation has been conducted on the feasibility of a dual-frequency radar system for the study of the morphology of subtropical precipitation. The system considered for empirical verification of the theoretical feasibility consists of two radars having wave lengths of 3.2 cm (AN/CPS-9) and 10.3 cm (WSR/TAM-1). Various techniques are examined for determination of in-cloud liquid-water content. It is shown that an estimate of water content can be made if the drop-size distribution can be characterized realistically by a two-parameter distribution function. Attenuation coefficients for 3.2 cm radiation are determined from data from the dual-frequency system. These are employed in a technique for estimating the drop-size distribution. Empirical relationships between radar reflectively and liquid-water content which utilize data from a single radar also are examined. The computed in-cloud liquid-water fields appear realistic. Fields of vertical motion are computed by use of the continuity equation for liquid-water concentration. These yield volume-integrated values which appear realistic for the type of radar echoes examined. Problems attendant to the estimation of precipitation intensity by use of a radar system are examined. Variations of the pertinent equations relating radar reflectivity and precipitation intensity with various parameters of drop-size distribution are shown. It is found that the characteristics of the dual-frequency system used in this research in Central Texas are not sufficiently sensitive for optimum utilization of the theoretical dual-frequency technique.