Observations of a Tropical Thunderstorm Using a Vertically Pointing, Dual-Frequency, Collinear Beam Doppler Radar

Abstract

This paper describes an investigation of a thunderstorm that occurred in the summer of 1991 over the National Astronomy and Ionosphere Center in Arecibo, Puerto Rico. Observations were made using collinear dual-wavelength Doppler radars, which permit virtually simultaneous observation of the same pulse volume using transmission and reception of coherent UHF and VHF signals on alternate pulses. This made it possible to directly measure the vertical wind within the sampling volume using the VHF signal while using the UHF signal to study the nature of the precipitation. The observed storm showed strong similarities with systems observed in the Global Atmospheric Research Program's Atlantic Tropical Experiment study. Since this experiment can determine the various microphysical parameters, such as the vertical air velocity, the mean fall speeds of the precipitation, and the reflectivity, the relationships between these parameters that have been postulated in past studies can be tested. For example, in this paper, the method of using reflectivities to deduce the fall speeds of precipitation particles is studied. The method is found to be unreliable when used in turbulent environments.