Institute for Computational Earch System Science, University of California, Santa Barbara
Leila M.V. de Carvalho
Department of Atmospheric Sciences, University of São Paulo, São Paulo, Brazil
(Manuscript received 22 October 1999, in final form 25 January 2000)
The climatology and interannual variability of heavy, or "extreme," precipitation events are studied, using station data from the state of Sao Paulo, Brazil. An extreme event is defined at each station when daily rainfall exceeds a certain percent of its seasonal or annual mean. It is found that these events occur mainly from November to March and that there is a distinct interannual variation in their number. The count of extreme events is not well correlated with mean precipitation. The relationship between extreme events and activity in the South Atlantic convergence zone (which, when active, is associated with increased precipitation) is therefore not obvious. From October to March, the interannual count of extreme events in the entire state is correlated positively with SST anomalies in the equatorial Pacific from near the date line to the west coast of South America. The interannual count at stations near the Atlantic coast from November to February is correlated positively with SST anomalies in the Atlantic Ocean near the latitude of Sao Paulo. In both cases the relationship between SST and mean precipitation is weak. The associations are confirmed with composites and rank correlations. The relationships described are apparent in the period 1976-77 to 1994-95. There is no correspondence evident between extreme events and SST if data beginning in 1948 are included in the analysis.