Radar observations of the development of tropical thunderstorms and convection cells using the Arecibo radar

Abstract

In the period from 13 Sept to 20 Sept 1979, the 430 MHz radar system at the Arecibo Observatory was used to study profiles of vertical velocity in developing and mature thunderstorms during the afternoon hours. During the eight day period, five days produced significant convective activity. The great sensitivity of the Arecibo radar facility al­lowed vertical velocities to be measured up to an altitude of 20 km. Since the tropopause over Puerto Rico is at an altitude of approximately 14 km at that time of year, the lower part of the stratosphere was also observed during the period of cloud development. Many studies have been carried out using Doppler radars to probe the interior of convective cells (see Wilson and Miller, 1972 for an excellent review and bibliography; also Battan, 1973). This is particularly true of radars operating at shorter wavelengths of 3 or 10 cm whích are more sensitive to reflections from precipitation within the clouds. The Arecibo radar, operating ata wavelength of 70 cm, receives echoes from variations in the index of refraction with a scale size of half the wavelength, or 35 cm. The fact that vertical velocities could be measured in both the troposphere and lower stratosphere is of particular interest.in view of the theory that the upward flux of mass in the tropical branch of the Hadley cell is concentrated in the cumulus towers (Riehl and Malkus, 1958; Reiter, 1975). Puerto Rico, at approximately 13°N latitude, is in this branch of the Hadley cell.