Influence of El Niño and La Niña events on Temperature in Southern South America

Surface temperature (ST) anomalies of El Niño (EN) and La Niña (LN) phases over southern South America (SSA) are shown and discussed in connection with the correspondent circulation and precipitation anomalies. ST data were taken from NCEP/NCAR reanalysis.

During the winter of years (0) of EN events as well as in autumn of year (+1), the upper level westerly flow over SSA is intensified at midlatitudes and decreases over the subtropical region. This is accompanied by an increase of the northerly flow at low levels in the subtropical region east of the Andes. Both features of the circulation anomalies favor warm anomalies over this region. The circulation features leading to cooler anomalies in most of Argentina and Uruguay varies from month to month during spring (0). During EN summer, there is no indication of a defined pattern on ST over SSA. In winter (+1) negative ST anomalies prevail over subtropical Argentina, southern Brazil and Uruguay, probably as a result of the northerly flow reduction at low levels.

During LN phases the ST anomalies are opposite in sign to those of EN, but generally starting a month earlier in the LN cycle. This is a consequence of a similar behavior in the circulation anomaly pattern of both cycles. The exception is in the autumn (+1) and winter (+1) when the signals are relatively weak due to the shorter duration of LN events.