Multi-Scale Nature of Tropical Influence on Precipitation Variability in Southern South America

The variability of summer precipitation in southern South America (SSA) exhibits a wide range of timescales, particularly from intraseasonal to decadal time scales, associated with different sources. The South America monsoon system influences the subtropical region particularly through the variability of the South Atlantic Convergence Zone. Moreover, tropical ocean variability influences South America remotely mainly through teleconnections. Large-scale climate patterns such as Madden-Julian Oscillation (MJO), on intraseasonal timescales, El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on interannual timescales as well as the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) on decadal timescales, provide a significant influence on the regional climate variability. In addition, the activity of the Southern Annular Mode (SAM) influences SSA region on similar band of timescales, reinforcing or weakening the tropical influence over the region.

The combined influence of these large-scale climate patterns over SSA has not been deeply studied yet although there are practical evidences of their occurrence. The talk will focus in describing the combined influence of ENSO and MJO in modulating the summer precipitation variability in southern South America. Depending on MJO phase, ENSO-related signal on SSA can be reduced or enhanced by MJO activity. Moreover, MJO-ENSO combined influence is exerted through changes on both divergent and rotational circulation anomalies in SH and in South America. The latter has important implications not only in the predictability levels but also on the development of wet and dry spells.