Rainfall during the Southern spring and early summer is of critical importance to agriculture in northeastern Argentina, Uruguay, and southern Brazil . In central Brazil (between 10° and 25°S) there is a pronounced dry season from April through August, and a pronounced rainy season from September through March. Rainfall increases over this region during September, as convection begins to shift southward from Central America to the Amazon Basin. In extreme southern Brazil (including most coastal sections north to near 20°S), Uruguay, and northeastern Argentina rainfall occurs more uniformly throughout the year. However, in these regions frost occurs regularly during May-August, thus limiting agricultural activities during this period. For the entire area from central Brazil south to northeastern Argentina planting begins during September and October.
Drier than normal conditions were observed over central Brazil (centered near 18°S, 50°W) during the entire period from September through December 1995 (Fig. 58). Over most of southern Brazil, near-normal to above-normal rainfall occurred during September and October, except for extreme southern Brazil where drier than normal conditions developed during October. Extremely dry conditions dominated nearly the entire region of central and southern Brazil during November, with many areas experiencing a continuation of the extremely dry conditions through December.
The patterns of outgoing longwave radiation (OLR) anomalies during this period (Fig. 59) indicate weaker-than-normal convection (positive OLR anomalies imply less-than-normal rainfall) over a large portion of South America, although the positive anomalies over Argentina also reflect a combination of above normal temperatures (Fig. 60a) and below normal rainfall (Fig. 60b). The intensification between October and November of drier-than-normal conditions over southern Brazil, Uruguay, and northeastern Argentina is also clearly evident in the OLR anomaly patterns.
