THE ROLE OF LOCAL CIRCULATIONS IN SUMMERTIME CONVECTIVE DEVELOPMENT AND NOCTURNAL FOG IN SAO-PAULO, BRAZIL

A non-hydrostatic, fully compressible, regional-scale numerical model of the atmosphere that includes parameterization of cloud microphysics is run in a two-dimensional mode. It uses two different observed vert ical profiles of temperature, relative humidity and wind to simulate t he local circulation evolution and impact on convection and nocturnal fog occurrence in Sao Paulo, Brazil. The atmospheric behaviour generat ed by the model is similar to the observations of the two summer days with and without sea breeze progression over the plateau. The convecti ve development occurs in the afternoon of the two experiments but with different features and intensities. In the experiment with sea-breeze progression, there is fog formation over the plateau during the follo wing night, in accordance with the observations. A strong northwesterl y flow acting in the lower troposphere, with intensity varying between 7 and 10 m s(-1), appears as an inhibiting agent of the sea-breeze pr ogression over the plateau and of convective development in the aftern oon and of the nocturnal fog occurrence. In this case, observed gusts during the night are well simulated and appear to be related to the to pography.