Low visibility study at Porto Alegre airport: numerical simulation with PAFOG model
DOI:
https://doi.org/10.6008/CBPC2179-6858.2019.006.0011Keywords:
Visibility, Radiation Fog, PAFOG ModelAbstract
Elaboration of this work was motivated by the lack of an effective visibility forecasting method for the Salgado Filho airport (Porto Alegre, RS). The main purposes are: 1) to simulate low visibility events caused by radiation fog at the Porto Alegre airport, using the PAFOG model and 2) evaluate the results of simulations started with different data sources. Vertical Profiles by radiosonde and forecasted using the data (CFSR-2) of the CFSR model were used for model initializations. Two sources of the surface data were used for initializations. Boundary layer (BL) variables were calculated with CFSR model data (reanalysis CFSR-1 and CFSR-2). Altitude data were obtained from radiosonde and CFSR-2 data (0.5° resolution). All (13) events of radiation fog were selected at the hours of radiosonde observations. The next physical conditions of the lower troposphere were analyzed: 1) synoptic and mesoscale analysis of NCEP and CFSR-1 (2.5° resolution) reanalysis products and GOES-12 satellite; 2) dynamic above the BL with CFSR-1 and CFSR-2 (0.5° resolution) and 3) vertical profile of the relative humidity (RH) from radiosonde and 0.5° CFSR-2 products. It was elaborated 25 initializations with radiosonde profiles and 48 with CFRS-2 profiles with antecedence up to 22h. Synoptic, dynamic and RH profile analyzes during the initialization showed favorable conditions for the use of the PAFOG model. Dew point extrapolation errors from CFSR-2 profiles were detected in some situations. An influence of the Frontal Systems (SF) extremities in some initializations generated geostrophic wind above the limit supported by the PAFOG model. PAFOG using CFSR-2 profiles simulated fog-like visibility in 36 initializations and did not simulate in 12 (10 due to errors in the relative humidity extrapolation and 2 due to SF influence). The best simulations of PAFOG with CFSR were started at 1200UTC at the day before the event and at 0000UTC at the event day. PAFOG with radiosonde profiles simulated fog-like visibility in 22 initializations and did not predict in 3. Results showed a great potential for the use of the PAFOG model for a fog forecasting at Salgado Filho airport, but also showed the necessity to adapt the model with the regional climatic condition.
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