Hydrologic visibility of weather radars operating in high-mountainous regions: A case study for the Toce catchment (Italy) during the mesoscale alpine programme

The use of weather radar systems in mountainous regions comes up against ma jor visibility problems due to (i) the interactions of the electromagnetic waves with the relief (ground clutter and screening effects) and (ii) the v ertical structure of the atmospheric reflectivities (bright band, partial b eam filling at cloud top). The concept of "hydrologic visibility" was propo sed to designate a procedure aimed at pre-determining the quality of rain-r ate measurements that a given weather radar system operating with a given s can strategy may obtain over a given hydrological catchment. A case study i s presented here to illustrate the procedure for the Toce catchment (1620 k m(2)), a high-elevation mountainous catchment in the Ticino Region, Italy, covered during the Mesoscale Alpine Programme (MAP) with three research and operational weather radars (S-Pol/NCAR, Ronsard/CETP, Monte-Lema/SMI). An inter-comparison of the performance obtained in terms of rain-rate estimati on errors with the various radars and various scanning strategies is realiz ed. (C) 2000 Elsevier Science Ltd. All rights reserved.