FOG FORECAST FOR THE INTERNATIONAL AIRPORT OF MACEIÓ , BRAZIL USING ARTIFICIAL NEURAL NETWORK

The different types of fog are defined in a general way as condensed water droplets in suspension in the atmosphere, very near the ground and able to decrease the horizontal visibility to less than 1km (INMET, 1999). In order to enhance fog forecast, It is important to know the several problems related to low visibility and the occurrence of fogs. Aeronautic operation restrictions in the airports, automobile accidents, health problems (especially when mixed the toxic residues and breathed) and many other problems are frequently caused by fog (Silveira, 2003; Oliveira, 1998). Had to the low computational and financial cost and the possibility of generation of trustworthy results using a meteorological station (a time that a good distribution of stations together with its generated information rare is accessible), a system for fog forecast is presented in this work in the International airport Zumbi of Palmares Maceió-Al, based in Artificial Neural Nets (RNAs) and in historical data, such as direction and speed of the wind, temperature and temperature of the dew point, visibility, etc, gotten in the meteorological station of the airport, being these used to validate and to construct a forecast model aiming at better to characterize and to identify this phenomenon. "RNA" consists of one technique of Artificial Intelligence, being its elaboration inspired in the cerebral structure human being and its capacity to assimilate very with the experience being used as regulating of function and recognized of standards. Therefore, in this work they had been used a description of hourly data during the year of 2004. The developed methodology revealed applicable standing out the how much bigger fact of the description and the quality of the best data the efficiency of the synthecized system of forecast. Different authors, Tubelis & Nascimento (1983) and Varejão-Silva (2000), have the same definition for fog, as being microscopical small a visible set of small drop of water liquid, in suspension in the atmosphere together to the ground, diminishing the horizontal visibility for less than 1 km (one kilometre). Some classifications exist how much to the type of fog, the most used it is the one that divides them in four main types (Woillett, 1928; Byers, 1959; Jiusto, 1981) is they: 1)Fog of radiation; 2)Fog of advection; 3)Fog frontal and 4)Others. Each type still presents subdivision that differentiate how much its gênesis. Amongst the main physical processes to analyze a forecast of formation of the fog they are distinguished the increase of the relative humidity of air, to put cooling or for addition ofvapour of water until the Temperature of the dew point (Td) becomes equal the Temperature of the air (T). In accordance with Peterssen (1940), the majority of fogs is produced by the cooling of air in contact with the surface of the Land. Peterssen noticed that the necessary conditions for the occurrence of one of these types of fog (of radiation) involve: high relative humidity, clean sky (or lightly cloudy), absence of wind and steady stratification of the atmosphere. On this work the classification of fogs was based on the horizontal visibility, being able to still classify them how much its intensity, in the following way: o Weak Fog: visibility between 1 km and 500m; o Moderate Fog: visibility between 500 100m; o Strong Fog: inferior visibility 100m. The reduction of the visibility observed had to the fog can cause accidents in the airports mainly. With the formation of the fog, the reduction of the visibility is a factor of risk for the diverse modalities of transports, as for example: aerial, closing airports, dislocating routes and provoking delay of the flights; marine, restricting the visibility; terrestrial e, causing accidents in the roads. In the industrial areas, the fog mixed toxic residues can provoke damages to the health. In agriculture the fog is favorable to the species of plants that need high relative humidity. Of this form, the forecast of the processes of formation of this phenomenon becomes in general essential for the planning of an organized and developed society and for the security of the transports. Amongst the transport pursuing, the most affected for the fog formation it is aviation. Aviation is extremely sensible to the weather conditions and its variations. A meteorological forecast of short term for the airports, with a good index of rightness, becomes essential in the monitoration of the responsible adverse phenomenos for the main occurred tribulation in the airports. The meteorological models for the weather forecast require onerous computational tools that allied to the classic sinotic analyses determine the