The role of urban boundary layer investigated by high resolution models and ground based observations in Rome area: a step for understanding parameterizations potentialities

The urban forcing on thermo-dynamical conditions can largely influences local evo- lution of the atmospheric boundary layer. Urban heat storage can produce notewor- thy mesoscale perturbations of the lower atmosphere. The new generations of high- resolution numerical weather prediction models (NWP) is nowadays largely applied 5 also to urban areas. It is therefore critical to reproduce correctly the urban forcing which turns in variations of wind, temperature and water vapor content of the plan- etary boundary layer (PBL). WRF-ARW, a new model generation, has been used to reproduce the circulation in the urban area of Rome. A sensitivity study is performed using di ff erent PBL and surface schemes. The significant role of the surface forcing 10 in the PBL evolution has been verified by comparing model results with observations coming from many instruments (LiDAR, SODAR, sonic anemometer and surface sta- tions). The crucial role of a correct urban representation has been demonstrated by testing the impact of di ff erent urban canopy models (UCM) on the forecast. Only one of three meteorological events studied will be presented, chosen as statistically relevant 15 for the area of interest. The WRF-ARW model shows a tendency to overestimate ver- tical transmission of horizontal momentum from upper levels to low atmosphere, that is partially corrected by local PBL scheme coupled with an advanced UCM. Depend- ing on background meteorological scenario, WRF-ARW shows an opposite behavior in correctly representing canopy layer and upper levels when local and non local PBL 20 are compared. Moreover a tendency of the model in largely underestimating vertical motions has been verified.