Análise de ocorrência de nevoeiros e dos resultados do modelo de previsão “PAFOG” em diferentes regiões climáticas do Brasil

Abstract

The main purpose of this study is to analyze the fog events occurrence, physical processes of a fog formation and results of a using of the PAFOG forecasting model in different climatic regions of Brazil. Surface weather variables for two years (2008-2009) at the airports in Porto Alegre and Confins cities and for 7 years (2008-2014) in the Salvador, Recife and Petrolina cities were analyzed. The active synoptic systems over the fog events were analyzed using the NCEP’s and CFSR’s reanalysis products. The tropospheric conditions were analyzed using vertical profiles by the observed radiosonde data and CFSR reanalysis data which were also used to initialise the PAFOG model. Eighty-two cases of fog in Porto Alegre with the duration between 10 minutes and 11 hours, occurring mainly in autumn and winter were found (one of the cases was rain). Twenty-three cases (13 cases of the radiation fog in the cyclone, and 10 cases in the frontal zone) were studied in detail. The frontal fog occurred at the frontal extremity (5 cases), between the frontal extremity and a barotropic cyclone (3 cases) and associated with the cyclogeneses (2 cases). It is important to emphasize that the description of the frontal fog in Brazil have never been described before. Seventy–fore fog cases with the duration between 10 minutes and 3 hours and occurred mainly in spring and summer were found in Confins. Fog was registered during the rain occurrence in 31 cases. Among the three cases selected for detailed analysis, two were the frontal fog and one was associated with POA. No any case of fog was found in Petrolina. Only one case of a short duration (10 minutes) for each location (occurring in autumn and winter, respectively, both associated with POA and accompanied with rain in Recife) was found in Salvador and Recife. All events selected were simulated using PAFOG model. The results were satisfactory in most events. Some forecasts were not satisfactory due to errors of the extrapolation of 2m dewpoint to the surface at the model initiation time; these errors were lower in winter. PAFOG model, initialized with the observed profiles by radiosond and with the CFSR reanalysis profiles, predicted all radiation fog in Porto Alegre. The best forecasts were those who were initialized at 1200 UTC the previous day. For the frontal fogs, PAFOG model initialized with the observed profiles forecasted 6 cases and did not forecast two cases, whereas with the CFSR reanalysis profiles the model forecasted 7 cases and 1 case was not forecasted. The PAFOG did not forecast any fog from 3 in Confins. In the NEB, model did not forecast fog in Recife, but forecasted fog in Salvador with 22 hours antecedence. Studies show the availability of the model using for the fog forecasting in Porto Alegre.