Utilité du radar Doppler dans l'étude des précipitations

The role of Doppler radar in the study of precipitation

Centre de recherches en Physique de l'environnement CNET/CNRS, Issy-les-Moulineaux

Abstract

Over the last ten years the Doppler meteorological radar has become a popular instrument for studying precipitation. Even today it still remains principally a research instrument for studying precipitation systems although development work on possible operational applications was recently started. In the introduction the operating principle of the Doppler radar is recalled showing that, in addition to the power of the echo received as in the case of conventional radar, it also can measure the radial velocity of cones in each field observed. The three conventional methods of using the Doppler radar for scientific purposes are then obtained. For each method, the principle together with recent modifications is described and physical quantities obtainable are illustrated by significant experimental results. The methodology of vertical shooting (part II) is examined whereby data on the vertical air speed and granulation of precipitation at the radar zenith can be recorded. Part III describes the conical speed method with one radar and the use of networks with two or more radars. The latter make it possible to observe the three-dimensional dynamics of air movement within a given precipitation system. Part IV briefly indicates recent operational applications based on rapid recognition of typical signals in reflectivity and radial velocity pictures which are provided with numbers and displayed on a colour screen. They are basically used for short-term forecasting of violent and dangerous phenomena (severity of near thunderstorms, tornadoes, gust fronts, turbulent zones...). Two possible future developments expected over the next few years are also mentioned : the rapid sweep Doppler radar and the airborne Doppler radar.