Ground-based remote sensing of wind, temperature and aerosol backscattering in an urban environment during different atmospheric stability conditions

The diurnal evolution of the urban boundary layer over the central area of Rome was observed by the simultaneous and co-located operation of a Doppler sodar, a microwave radiometer and a dual polarization lidar. The Doppler sodar was configured to provide a wind profile up to about 800 m, and a time-height picture of the thermal structure of the urban boundary layer. A microwave radiometer provided a temperature profile up to 600 m with a height resolution of 50 m. The lidar provided profiles of the aerosol backscattering up to about 7-10 km with 30 m height resolution. The experiment was conducted for several days in the year 1998 during day and night with clear sky and low wind. The aerosol profiles in the urban troposphere appear linked to stability conditions in the lower layers and strong pollution. The presence of aerosols, typically in the afternoon hours at heights up to 2-3 km, can be related to a relatively high mixed layer. Such layer is caused by free convection as indicated by the Richardson number, estimated by the temperature and wind data. Some typical case studies are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.