Interannual variability of the Tropical Atlantic independent of and associated with ENSO: Part II. The South Tropical Atlantic

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The interannual variability of the tropical Atlantic ocean-atmosphere system is examined using 50 years of sea-surface temperature (SST) and re-analysis data, and satellite data when available. A singular value decomposition analysis of 12-to 72-month bandpass filtered SST and zonal wind stress reveals two dominant modes of interannual variability. The SST anomalies are confined to the North Tropical Atlantic (NTA) in the first mode and extend over the equatorial and South Tropical Atlantic in the second mode. No evidence is found for an Atlantic SST dipole. The structure of the first (NTA) mode is examined in detail here, while the second mode has been described in a companion paper. In particular, the relationship of the NTA mode with El Niño-Southern Oscillation (ENSO) is investigated. There are 12 NTA events (seven warm and five cold) that are associated with ENSO, and 18 NTA events (seven warm and 11 cold) that are independent of ENSO.The ENSO-associated NTA events appear to be a passive response to remote ENSO forcing, mainly via a Pacific-North America (PNA)-like wave train that induces SST anomalies over the NTA through changes in the surface wind and latent heat flux. The NTA anomalies peak four months after ENSO. There does not appear to be an atmospheric response to the NTA SST anomalies as convection over the Atlantic is suppressed by the anomalous Walker circulation due to ENSO.The ENSO-independent NTA events also appear to be induced by an extratropical wave train from the Pacific sector (but one that is independent of Pacific SST), and forcing by the North Atlantic Oscillation (NAO) also contributes. As the event matures, the atmosphere does respond to the NTA SST anomalies, with enhanced convection over the Caribbean and a wave train that propagates northeastward to Europe.

Section: Discussionmentioning

confidence: 99%

“…We present an overview of the analysis and detailed results for the NTA mode. The detailed results for the STA mode will be described in a companion paper (Handoh et al, 2006). It is worth noting that there is significant decadal-scale variability in the tropical Atlantic as well (e.g.…”

Section: Introductionmentioning

confidence: 99%

Interannual variability of the tropical Atlantic independent of and associated with ENSO: Part I. The North Tropical Atlantic

Handoh

Matthews

Bigg

et al. 2006

Self Cite

“…Handoh et al (2006b), using the SST data for the 1948–1999 period, analysed the influence of the ENSO on the AEM. They found that some AEM events are ENSO dependent, and others ENSO independent.…”

Section: Introductionmentioning

confidence: 99%

Evolving anomalous SST patterns leading to ENSO extremes: relations between the tropical Pacific and Atlantic Oceans and the influence on the South American rainfall

Kayano

Andreoli

Souza

2011

Several studies have provided observational and numerical evidence that the tropical Pacific and Indian Oceans are influenced by the tropical Atlantic within a one season time scale. The influence of the Atlantic equatorial mode (AEM) in the Pacific El Niño-Southern Oscillation (ENSO) mode is observationally re-examined. The analyses focus on the ENSO-related evolving sea surface temperature (SST) and sea level pressure (SLP) anomalies in the Tropics that follow the occurrences of AEM events and those that are independent of the AEM. The cold (warm) AEM followed by El Niño (La Niña) shows a sequence of maps that might be explained by the mechanism previously outlined on the relationship of the tropical Atlantic and the other tropical Oceans. This mechanism involves an anomalous Atlantic Walker circulation and a Gill-Matsuno-type atmospheric response to anomalous cooling or warming in the tropical Atlantic. The seasonal timing of the relationship studied differs from that of the previous studies. Here, it is noted that the Atlantic SST anomalous conditions are persistent and might be noted 5-6 months before that proposed in previous results. Furthermore, the ENSO extreme conditions are reinforced and maintained by the east-west SST anomalous gradient in the tropical Pacific. Also, the precipitation composites over South America for the ENSO extremes, which are AEM-dependent and AEM-independent cases, are discussed. The AEM-dependent ENSO extremes combine the effects from the tropical Pacific, and equatorial and tropical South Atlantic on the rainfall over South America. The results presented here, to the authors' knowledge, have not been discussed before and might represent a potential for long lead predictability of the climate variations in the tropical Pacific.

“…Comparison of SST, SLP and low‐level wind composites for the PGRAD_TNA and NGRAD_TNA (PGRAD_TSA and NGRAD_TSA) events and for the ENSO independent TNA (TSA) mode studied by Handoh et al . () (Handoh et al, ) indicate similarities in the common area of both analyses. However, the present analysis indicates differences associated with the modes in each TA side, in particular concerning their effects on precipitation.…”

Section: Discussionmentioning

confidence: 94%

How the two nodes of the tropical Atlantic sea surface temperature dipole relate the climate of the surrounding regions during austral autumn

Kayano

Andreoli

Garcia

et al. 2018

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 Niño (EN) (a La Niña, 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 Niño‐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.