Influência de diferentes tipos de ENOS na precipitação na América do Sul

Abstract

The impacts of the different ENOS types, defined as Central-Pacific (CP) type, the Eastern- Pacific (EP) type, or the Mixed (MIX) type (i.e. the both types coexist) on interannual rainfall variability over South America are investigated. The emphasis is on the South American rainy season which is comprised of austral summer and autumn periods. During austral summer the South America shows negative (positive) rainfall anomalies over north region associated with the anomalous descending branch of the Walker circulation during El Niño MIX and EP (La Niña CP and MIX) event. However during El Niño CP, the tropical regions experience below average rainfall generated by anomalous descending branch of the Walker circulation effecting throughout the region. The subtropics feature intense (weak) positive rainfall anomalies associated with an anomalously strong (weak) South American Low Level Jet (SALLJ) during El Niño EP (El Niño CP). For the La Niña the weakening of the SAJJL results in the drier conditions during the La Niña MIX event. During autumn season the northeast (south and southeast) South America features intense negative (positive) rainfall anomalies during El Niño EP, contrasting with El Niño MIX e CP conditions. The shift in the anomalous warming location during El Niño MIX leads to anomalous subsidence over the eastern northwestern AS. Consequently, this favours the normal seasonal migration of the Atlantic ITCZ allowing the Atlantic SST to reinforce the associated convection favouring positive rainfall anomalies. On other hand, for On the other hand, during EP and CP events, warming in the tropical north Atlantic keeps ITCZ further north, inhibiting convective activity over the northeastern AS, leading to negative precipitation anomalies in this region. For the La Niña events the tropical precipitation pattern during CP events is linked to changes in atmospheric circulation associated with the interbasin gradient between the Pacific and Atlantic of the sea level pressure anomalies, while for the MIX event, local effects appear to be most important. The result of this study might be useful mainly for climate monitoring purposes.