CONVECTIVE CHARACTERISTICS OF THE NOCTURNAL URBAN BOUNDARY-LAYER AS OBSERVED WITH DOPPLER SODAR AND RAMAN LIDAR

Convective plume patterns, characteristic of clear sky and light wind daytime boundary layers over land, were observed for two nights with a tri-axial Doppler sodar operated in the central area of Rome during t he summer of 1994. An urban heat island effect, combined with a contin uation of a breeze from the sea late into night during both days, is b elieved to be responsible for the observed nocturnal convection. Estim ates of the surface heat flux and the vertical velocity scaling parame ter are obtained from profiles of vertical velocity variance, and the Raman lidar water vapor measurements are used to obtain the humidity s caling parameter. Convective scaling results for vertical wind and hum idity fairly agree with the results of other experiments and models. O n the basis of available measurements, it appears that mixed-layer sim ilarity formulations used to characterize the daytime convective bound ary layer over horizontally homogeneous surfaces can also be applied t o the nocturnal urban boundary layer during periods of reasonable conv ective activity.