Comprehensive observation research on urban atmospheric boundary layer — Description of field experiment and analysis of micrometeorological properties in the surface layer

Two field observation experiments in Nanjing aimed at urban boundary layer researches were described. The observation data were analyzed and some micrometeorological properties in the urban surface layer were obtained. The main results are: Air temperature in the urban area is significantly higher than in the suburban area, which embodies the presence of urban heat island effect, and the differences of air temperature between the urban and suburban areas decrease with height. During the observation period in the winter of 2006, wind speed in the urban area is about 1 m/s less than in the suburban area, which reflects the damping, friction and drag effects of urban buildings on the airflow. Sensible heat flux in the daytime in the urban area is approximately equivalent to that in the suburban area, but latent heat flux in the urban area is far less than in the suburban area, thus the Bowen ratio in the urban area is far larger than in the suburban area. In the summer, friction velocity in the urban area is 34% larger than in the suburban area, and is 23% larger in the winter. In this paper, a new variable, normalized friction velocity, was introduced, of which the mean value was found a constant not varying with time and season. It is found that the proportion of vertical turbulent energy to total turbulent energy in the urban area is somewhat larger than in the suburban area during the winter of 2006.