88th Annual Meeting (20-24 January 2008)

Tuesday, 22 January 2008: 11:30 AM
Meteorological conditions contributing to the development of thunderstorms in the city of São Paulo, Brazil
222 (Ernest N. Morial Convention Center)
Carlos A. R. Morales, University of Sao Paulo, São Paulo, Brazil; and R. Porfirio da Rocha and R. J. Bombardi
This study presents the main meteorological components associated with the development of thunderstorms over the city of São Paulo during the summers of 2000 through 2004. The main work is based on hourly measurements of air-temperature (T), web-bulb temperature (Tw), pressure (P), wind velocity and direction, rainfall and thunder and lightning observations observed at the Meteorological Weather Station of the University of São Paulo located in the southern region of the city. The analysis consists in diagnosing the mean diurnal cycle of these meteorological variables as a function of days with and without-thunderstorm. The wind diurnal cycle shows that for the days with thunderstorms the morning flow is from northwest rotating to southeast after 16:00 local time and it remains from east until the night. For the days without thunderstorms, the wind is well characterized by the sea-breeze circulation that in the morning has the wind flowing from northeast and in the afternoon from southeast. In terms of air temperature, the thunderstorms days show that the air temperature diurnal cycle presents higher amplitude and the maximum temperature of the day is 3.2 degrees C higher than in days without thunderstorms. Another important factor found is the difference between moisture that is higher during thunderstorm days. In terms of precipitation, the thunderstorm days are responsible for more than 60% of the total rain accumulation during the summer, which characterizes the convective development of such clouds. Moreover, the rainfall distribution shows that thunderstorm days have higher rainfall rate intensities and an afternoon precipitation maximum; while in the days without thunderstorms there isn't a defined precipitation diurnal cycle.

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