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Comparing WRF PBL schemes with experimental data over Northern Italy

pubblicazioni - Poster

Comparing WRF PBL schemes with experimental data over Northern Italy

La corretta ricostruzione delle variabili meteorologiche che determinano la dispersione degli inquinanti in atmosfera costituisce un requisito essenziale per una valutazione affidabile della qualità dell’aria e degli effetti di eventuali politiche di riduzione delle emissioni, ivi inclusi quelli determinati da politiche di efficienza energetica.

Planetary Boundary Layer (PBL) plays a key role in determining ground concentrations of pollutants, especially in densely populated areas characterized by weak circulation conditions, such as the Po Valley. Nevertheless, the determination of PBL height remains one of the most uncertain parameters in modeling estimation, strongly affecting the reconstruction of dispersion processes and, thus, ground concentrations. A sensitivity test has been conducted on PBL by comparing experimental data and different model simulations in order to assess the skill of the WRF meteorological model in reproducing its structure and evolution. Five PBL scheme have been selected and compared to particle vertical profiles by balloon soundings, meteorological balloons and Lidar measurements. Particle vertical profiles were collected in the metropolitan area of Milan by means of a tethered balloon equipped with an optical particle counter and a meteorological station as well as by a Lidar instrument. PBL height was derived in both cases using a gradient method. Additionally, meteorological soundings of Milano Linate airport were considered too. The availability of this set of highly specialized experimental data represented an unprecedented opportunity for model evaluation over Northern Italy. WRF has been applied for July 2007 and February 2008 over three nested domains, with the last one focused on the Po Valley area with a spatial resolution of 5 km. Initial and boundary conditions were obtained from the ECMWF analysis fields. Only the 5 km domain was compared to observations. Results show substantial differences among the five schemes, and between these and observations. The schemes generally overestimate PBL height (BIAS = 41 to 134 m in winter; BIAS = 39 to 219 m in summer), but they show a correlation index always higher than 0.5. For each scheme the main parameterizations are discussed as well as their effects on PBL and meteorological fields reconstruction.

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