Análise e previsão de visibilidade baixa no aeroporto de Maceió

Abstract

Study of Low visibility is very important for security and air traffic efficiency. Surface meteorological variables, associated to low visibility at the Maceio Airport, were analyzed during five years 2002-2005 and 2007, using observational data from the surface weather station at the airport. Synoptic conditions that prevailed before and during the fog events were studied using different reanalysis products of NCEP and ECMWF. It was obtained that only mist is able to decrease severely the horizontal visibility in Maceio and to formed fog. Mist decreased the visibility to less than 5km in 14% of the observations. A great portion of the visibilities between 1-3km (88%) were associated to rain occurrence. Haze rarely decreases the visibility to less than 5km and the main reasons are its acting time (at noon) and stronger winds (over 3m/s). The most frequently conditions associated to low visibility are calm or weak winds (under 3m/s) from ocean and high humidity (>95%). The period of higher frequency of low visibility is between May and September. Eight events of fog have been identified in this study. Fog duration varied from 20 minutes up to 4 hours and its intensity was weak or moderate. Fog events were associated to synoptic systems, such as: 1) Wave Disturbances in Trade Winds; 2) disturbances arising from the cold front extremity. The temperature profile predicted by WRF has represented the conditions for fog formation better than NCEP. The typical temperature profile for fog events by WRF showed: 1) a temperature inversion from surface up to 166m (985hPa); 2) humid layer (T-Td between 0,3°C and 1,6°C) up to the top of inversion; 3) existence of conditional instability above the inversion layer between 985-860hPa; 4) a drier and stable layer above 860hPa. PAFOG model was used for fog forecast in three cases, which have passed of criterion for model using. Forecast was satisfactory just in one case (in 30% of the predictions). Satisfactory results of fog duration and intensity were obtained with 10 hours of antecedence.