MIXING HEIGHTS AND WIND DIRECTION ANALYSIS FOR URBAN AND SUBURBAN AREAS OF BUENOS-AIRES CITY

Monthly mean maximum mixing depths have been computed for an eleven-year period (1972-1982) for three meteorological stations in Buenos Aires city, Argentina, and its surroundings. The stations are: Aeroparque, at 100 m from the coast of the La Plata River in the northeast of the city; Buenos Aires Central Observatory (BACO), at 8 km westward from the preceding station, and Ezeiza Aero located 33 km southwestward from the BACO. A monthly mean maximum mixing depth distribution which showed minimum values in July and maximum values in January was found. A minimum mixing depth value of 732 m appeared in Aeroparque and a maximum of 1566 m in Ezeiza Aero. A marked spatial decrease in the monthly mean depth for the coastal station was observed in summer. A water-earth breeze at the maximum temperature hour could influence the mixing layer in this season. No effect was observed in winter. The influence of the wind direction on the mixing height has also been studied. In summer, mixing heights between 400 and 1600 m were more frequent when the wind came from N - E, than when it came from S - W, for Aeroparque. Far from the coastline this difference decreased. This effect was not observed in winter.