Influence of the Madden Julian Oscillation on precipitation and surface air temperature in South America

ALVAREZ, M.; VERA, CAROLINA; KILADIS, GEORGE; LIEBMANN, BRANT

CLIMATE DYNAMICS

SPRINGER

Lugar: Berlin; Año: 2016 vol. 46

0930-7575

The regional influence of the Madden?Julianoscillation (MJO) on South America is described. Mapsof probability of weekly-averaged rainfall exceeding theupper tercile were computed for all seasons and relatedstatistically with the phase of the MJO as characterizedby the Wheeler?Hendon real-time multivariate MJO(RMM) index and with the OLR MJO Index. The accompanyingsurface air temperature and circulation anomalieswere also calculated. The influence of the MJO onregional scales along with their marked seasonal variationswas documented. During December?February whenthe South American monsoon system is active, chances ofenhanced rainfall are observed in southeastern South America(SESA) region mainly during RMM phases 3 and 4,accompanied by cold anomalies in the extratropics, whileenhanced 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 attenuatedin the extratropics. Conversely, in June?November,reduced rainfall and cold anomalies are observed near thecoast of the SACZ region during phases 4 and 5, favored by upper-level convergence over tropical South America andan anticyclonic anomaly over southern South America. InSeptember?November, enhanced rainfall and upper-leveldivergence are observed in the SACZ region during phases7 and 8. These signals are generated primarily through thepropagation of Rossby wave energy generated in the regionof anomalous heating associated with the MJO.