资源环境科技发展态势分析平台

The relations of both nodes of the tropical Atlantic (TA) cross-equatorial sea surface temperature (SST) gradient (GRAD) mode to the climate of northeast Brazil (NEB) during the 1901-2012 period are examined separately. The GRAD mode consists of a SST anomalous pattern anti-symmetric about the equator with centres in the region of the northeasterly and southwesterly trade winds. The positive GRAD (PGRAD) (negative GRAD [NGRAD]) modes defined by their northern or southern nodes are considered separately, as well as, if they are preceded or not by an El Nino (EN) (a La Nina, LN). The PGRAD mode defined by the northern (southern) node and preceded by an EN is indicated by PGRAD_TNA_EN (PGRAD_TSA_EN), and that not preceded by an EN is indicated by PGRAD_TNA (PGRAD_TSA). The corresponding NGRAD modes are indicated by NGRAD_TNA_LN, NGRAD_TSA_LN, NGRAD_TNA and NGRAD_TSA. Our analysis is limited to the NEB rainy season (March-May), when the GRAD mode is more pronounced and the NEB rainfall is more closely related to the TA SST variations. In general, the South Atlantic subtropical high is crucial in defining the cross-equatorial flow, responsible for the anomalous meridional positioning of the Atlantic inter-tropical convergence zone. When a positive (negative) dipole-like SST anomaly pattern is established in the TA, the negative (positive) rainfall anomalies occupy most of NEB. This is the case of the PGRAD_TSA_EN, PGRAD_TNA, NGRAD_TSA_LN and NGRAD_TNA_LN. Most of the GRAD modes defined by TNA are also related to the El Nino-Southern Oscillation (ENSO), in such a way that an EN (a LN) precedes a PGRAD (NGRAD) event, and most of the GRAD modes defined by TSA do not depend on the ENSO. Also, the PGRAD events are well distributed during both Atlantic multidecadal oscillation phases and the NGRAD events occur preferably during its cold phase.