Are Atlantic Niños enhancing Pacific ENSO events in recent decades?

Abstract

This work presents observational evidence of a change in Atlantic‐Pacific Niños connection since the late 60's. Accordingly, summer Atlantic Niños (Niñas) alter the tropical circulation favoring the development of following‐winter Pacific Niñas (Niños). The same change is obtained in an ensemble of AGCM integrations in which SSTs in the Atlantic are the observed in 1949–2002 and those in the tropical Indo‐Pacific are from a coupled OGCM. The mechanism (for the positive Atlantic phase) involves the strengthening of the Walker circulation with ascending branch over the Atlantic and descending branch over the central Pacific. The enhanced surface divergence in the latter region shallows the equatorial thermocline triggering coupled processes, and favoring the development of a Pacific La Niña. Results could be linked to the reported 60's and 70's climate shifts; emphasizing the importance of tropical Atlantic for the success of seasonal forecast skill.

The South Atlantic Anticyclone as a key player for the representation of the tropical Atlantic climate in coupled climate models

“…The atmospheric bridge paradigm relates SST warming in the tropical Atlantic Ocean to enhanced subsidence and reduced cloudiness as a consequence of warmer eastern Pacific waters. On the other hand, Atlantic Niños seem to enhance Pacific Niño events in recent decades (Rodríguez-Fonseca et al 2009;Ding et al 2012). Future work should therefore also analyze in detail the interaction of the northern and southern hemispheric subtropical anticyclones in the Atlantic Ocean with both the Atlantic and Pacific Hadley and Walker cell systems.…”

Symmetry of the Atlantic Niño mode

“…We use monthly fields of ocean temperature, wind stress, and heat flux from the Ocean Reanalysis System 4 (ORA-S4) of the European Centre for Medium-Range Weather Forecasts (ECMWF) [Balmaseda et al, 2013] [Carton and Giese, 2008] for the same time period as for ORA-S4, namely, 1958to 2009.4 is forced with 20CRv2 surface winds [Compo, 2011] and has 40 vertical levels and a horizontal resolution of 0.25°. We have calculated interannual anomalies by subtracting a mean seasonal cycle as well as the linear trend of the time series.…”

“…Understanding the Atlantic Niño mode variability is of socioeconomic importance as SST anomalies in the eastern equatorial Atlantic are related to precipitation over Northeast Brazil [Ruiz-Barradas et al, 2000] and the onset of the West African monsoon [Brandt et al, 2011a]. The equatorial Atlantic also affects the equatorial Pacific Ocean [e.g., Rodriguez-Fonseca et al, 2009], so that accounting for equatorial Atlantic SST variability may improve the prediction of El Niño events [Keenlyside et al, 2013].…”

On the spatial coherence of rainfall over the Saloum delta (Senegal) from seasonal to decadal time scales

“…More specifically, several studies have focused on SST-driven variability of Sahel rainfall (e.g., Hoerling et al, 2006;Hagos and Cook, 2008;Caminade and Terray, 2009;Mohino et al, 2010;Rodríguez-Fonseca et al, 2011). Many significant links have been found, especially at seasonal to decadal timescales, and it has also been shown that, these teleconnections might evolve with time: for example, the sign of the regression Frontiers in Earth Science | www.frontiersin.orgbetween SST anomalies in the equatorial Atlantic and in the Pacific has changed after the 1970s (Rodríguez-Fonseca et al, 2009).…”