The seasonal cycle of the intraseasonal (IS) vari-1 ability of precipitation in South America is described through 2 the analysis of bandpass filtered outgoing longwave radi-3 ation (OLR) anomalies. The analysis is discriminated be-4 tween short (10-30 days) and long (30-90 days) intrasea-5 sonal timescales. 6 The seasonal cycle of the 30-90-day IS variability can be 7 well described by the activity of first leading pattern (EOF1) 8 computed separately for the wet season (October-April) and 9 the dry season (May-September). In agreement with previ-10 ous works, the EOF1 spatial distribution during the wet sea-11 son is that of a dipole with centers of actions in the South 12 Atlantic Convergence Zone (SACZ) and southeastern South 13 America (SESA), while during the dry season, only the last 14 center is discernible. In both seasons, the pattern is highly 15 influenced by the activity of the Madden-Julian Oscillation 16 (MJO). Moreover, EOF1 is related with a tropical zonal-17 wavenumber-1 structure superposed with coherent wave trains 18 extended along the south Pacific during the wet season, while 19 during the dry season the wavenumber-1 structure is not ob-20 served.

The regional influence of the Madden-Julian Oscillation (MJO) on South America is described.Maps of probability of weekly-averaged rainfall exceeding the upper tercile were computed for all seasons and related statistically with the phase of the MJO as characterized by the Wheeler-Hendon Real-Time Multivariate MJO (RMM) index and with the OLR MJO Index (OMI). The accompanying surface air temperature and circulation anomalies were also calculated.The influence of the MJO on regional scales along with their marked seasonal variations was documented. During December-February when the South American monsoon system is active, chances of enhanced rainfall are observed in southeastern South America (SESA) region mainly during RMM phases 3 and 4, accompanied by cold anomalies in the extratropics, while enhanced rainfall in the South Atlantic Convergence Zone (SACZ) region is observed in phases 8 and 1. The SESA (SACZ) signal is characterized by upper-level convergence (divergence) over tropical South America and a cyclonic (anticyclonic) anomaly near the southern tip of the continent. Impacts during March-May are similar, but attenuated in the extratropics. Conversely, in June-November, reduced rainfall and cold anomalies are observed near the coast of the SACZ region during phases 4 and 5, favored by upper-level convergence over tropical South America and an anticyclonic anomaly over southern South America. In September-November, enhanced rainfall and upper-level divergence are observed in the SACZ region during phases 7 and 8. These signals are generated primarily through the propagation of Rossby wave energy generated in the region of anomalous heating associated with the MJO.