The Impacts of Inter–El Niño Variability on the Tropical Atlantic and Northeast Brazil Climate

Abstract

In this study, observations and numerical simulations are used to investigate how different El Niño events affect the development of SST anomalies in the Atlantic and how this relates to the Brazilian northeast (NE) precipitation. The results show that different types of El Niño have different impacts on the SST anomalies of the equatorial and tropical South Atlantic but a similar SST response in the tropical North Atlantic. Strong and long (weak and short) El Niños with the main heating source located in the eastern (central) Pacific generate cold (warm) anomalies in the cold tongue and Benguela upwelling regions during boreal winter and spring. When the SST anomalies in the eastern equatorial and tropical South Atlantic are cold (warm), the meridional SST gradient across the equator is positive (negative) and the ITCZ is not allowed (allowed) to move southward during the boreal spring; as a consequence, the precipitation is below (above) the average over the NE. Thus, strong and long (weak and short) El Niños are followed by dry (wet) conditions in the NE. During strong and long El Niños, changes in the Walker circulation over the Atlantic and in the Pacific–South Atlantic (PSA) wave train cause easterly wind anomalies in the western equatorial Atlantic, which in turn activate the Bjerknes mechanism, establishing the cold tongue in boreal spring and summer. These easterly anomalies are also responsible for the Benguela upwelling. During short and weak El Niños, westerly wind anomalies are present in the western equatorial Atlantic accompanied by warm anomalies in the eastern equatorial and tropical South Atlantic; a positive phase of the South Atlantic dipole develops during boreal winter. The simulations highlight the importance of ocean dynamics in establishing the correct slope of the equatorial thermocline and SST anomalies, which in turn determine the correct rainfall response over the NE.

Growth and decay of the equatorial Atlantic SST mode by means of closed heat budget in a coupled general circulation model

“…Following the former argument, Lübbecke and McPhaden (2012) have discussed the different equatorial Atlantic responses from ENSO forcing and they have pointed out the conditions over the NTA as the responsible for a delayed feedback through Rossby wave propagation. De Almeida and Nobre (2012) have suggested from observations how ENSO weaken the equatorial Atlantic variability while Rodrigues et al (2011) have confirmed the different impacts of Pacific El Niño-types over the Equatorial Atlantic.…”

Climatic characteristics of the 2010-2016 drought in the semiarid Northeast Brazil region

“…This is mainly due to the dependence of its rainy season upon oceanic and atmospheric conditions in the tropical Pacific and Atlantic Oceans. Previous studies using dynamic and statistical modeling have demonstrated that the relationship between oceanic and atmospheric conditions in the equatorial Pacific and tropical Atlantic and the seasonal rainfall over the northern part of the Brazilian Northeast allows large climate events to be forecasted with a lead time of a few months (Hastenrath 1990, Hastenrath and Greischar 1993, Marengo et al 2013, b, Giannini et al 2004, Nobre et al 2006, Rodrigues and McPhaden 2014, Rodrigues et al 2011, Hounsou-Gbo et al 2016, among others).…”

Assessing vegetation variability and trends in north-eastern Brazil using AVHRR and MODIS NDVI time series

“…Not all El Niño phases result in a drought in NEB, however [Kane, 1997;Erasmi et al, 2009]. Recently, Rodrigues et al [2011] showed that the inter-El Niño variability has to be taken into account, when accessing the effects of El Niño phases on precipitation in NEB. The authors highlighted that strong and long (weak and short) El Niño phases lead to dry (wet) conditions in NEB.…”