Climatological analysis of wintertime extreme low temperatures in Sao Paulo City, Brazil:: Impact of sea-surface temperature anomalies

A diagnostic climatological Study of winter cold temperature extremes in the Metropolitan Area of Sao Paulo (NIASP) is presented. This diagnosis is based on temperature data collected at the Meteorological Station of Parque Estadual das Fontes do lpiranga (IAG/USP) from 1950 to 2000. The persistence of synoptic and climatological patterns has been studied through principal component (PC) analysis and the results are compared with monthly anomalies in sea-surface temperature (SST) of the eastern Pacific and South Atlantic. The extreme cold air temperatures, on a monthly basis, have shown no significant change since 1950. On the other hand, the mean monthly air temperatures have shown a slight warming trend, in agreement with the South Atlantic Ocean warming trend. The PC indicates significant loadings of two SST anomaly types: a cold anomaly of the South Atlantic Ocean, and a warm anomaly off the southern Brazilian coast. The latter could also be responsible for some extreme cold events (for daily minimum temperatures) in the MASP, and to a dominant westerly wind direction (southwest to northwest). Both the cold events and the westerly wind direction were evident in such winters as 1953, 1975, 1978, 1981, and 1994. On the other hand, the cold mean monthly temperatures are very well correlated to a broad cold pool anomaly in the South Atlantic at around 25 to 35 degreesS and 15 to 55 degreesW - sometimes narrower (such as in 1979 and 1988), and sometimes broader (Such as 1964 and 1990). Where there was a narrowing or a widening, the prevailing wind direction was from the south-southeast. Therefore, the conclusion of these results is that the SST anomalies in the South Atlantic Ocean have a dominant effect on the Sao Paulo winter temperature climatology. Copyright (C) 2002 Royal Meteorological Society.