Changes in the interannual variability of the tropical Pacific as a response to an equatorial Atlantic forcing

Abstract

SUMMARY: Previous studies have reported that the tropical Atlantic has had an influence on tropical Pacific interannual variability since the 1970s. This variability is studied in the present work, using simulations from a coupled model in the Indo-Pacific but with observed sea surface temperature (SST) prescribed over the Atlantic. The interannual variability is compared with that from a control simulation in which climatological SSTs are prescribed over the Atlantic. Differences in the Pacific mean state and in its variability are found in the forced simulation as a response to a warming in the equatorial Atlantic, characterized by a cooler background state and an increase in the variability over the tropical Pacific. A striking result is that the principal modes of tropical Pacific SST interannual variability show significant differences before and after the 1970s, providing new evidence of the Atlantic influence on the Pacific Ocean. Significant cooling (warming) in the equatorial Atlantic could have caused anomalous winds in the central-easter Pacific during the summer since 1970s. The thermocline depth also seems to be altered, triggering the dynamical processes involved in the development of El Niño (La Niña) phenomenon in the following winter. An increase in frequency of Niño and Niña events favouring the Central Pacific (CP) ones is observed in the last three decades. Further analyses using coupled models are still necessary to help us to understand the causes of this inter-basin connection.Keywords: Tropical Atlantic variability, Atlantic-Pacific connection, ENSO.RESUMEN: Cambios en la variabilidad interanual del PaCífiCo troPiCal Como resPuesta a un forzamiento del atlántiCo eCuatorial. -Trabajos previos han puesto de manifiesto como el Atlántico Tropical influye en la variabilidad interanual del Pacífico a partir de los años 70. El presente trabajo estudia la variabilidad del Pacífico Tropical a partir de simulaciones realizadas con un modelo acoplado en el Indo-Pacífico que considera la Temperatura de la Superficie del Mar (TSM) observada en el Atlántico como forzamiento externo. Los resultados de esta simulación son comparados con los obtenidos en una simulación de control, con TSM climatológicas en el Atlántico. La simulación forzada muestra cambios en el estado base y la variabilidad del Océano Pacífico relacionados con un calentamiento en el Atlántico ecuatorial, destacando un aumento de la variabilidad y un enfriamiento del Pacífico ecuatorial. Además, los principales modos de variabilidad del Pacífico antes y después de los 70 son diferentes, reafirmándose la influencia del Atlántico sobre el Océano Pacífico. Un enfriamiento (calentamiento) en el Atlántico ecuatorial podría generar vientos anómalos en el centro-este de la cuenca del Pacífico durante el verano desde dicha década. La profundidad de la termoclina también se modificaría, desencadenándose los procesos dinámicos involucrados en el desarrollo de El Niño (La Niña) en el invierno siguiente. Los resultados muestran un aumento de la frec...

The Teleconnection of the Tropical Atlantic to Indo-Pacific Sea Surface Temperatures on Inter-Annual to Centennial Time Scales: A Review of Recent Findings

“…In addition, both observations and ATL_VAR show strongest correlations at the beginning and the end of the 20th century, and overall weaker correlations in the middle of the century, although the phasing is somewhat different between observations and the model. Overall, the results from this analysis are consistent with the recent work by [4,10,11]. …”

“…These results are consistent with what has been reported in [16]. The descending (ascending) motions in the central Pacific lead to anomalous easterlies (westerlies) in the central-western Pacific that trigger an upwelling (downwelling) oceanic Kelvin wave propagating eastward during the following months ( [9,10]). As the Kelvin wave propagates, the eastern Pacific becomes cooler (warmer) through the activation of the thermocline feedbacks and the establishment of the Bjerknes feedback ( [9]).…”

“…Overall, the correlations for the whole period (1901 to 2010) are negative, as expected from the mechanism identified in the previous sections (-0.35 for observations and -0.36 for ATL_VAR, both statistically significant at the 95% confidence level). However, as suggested by [4,10,11], there are strong decadal variations in both the observations and ATL_VAR. In addition, both observations and ATL_VAR show strongest correlations at the beginning and the end of the 20th century, and overall weaker correlations in the middle of the century, although the phasing is somewhat different between observations and the model.…”

Impacts of the Atlantic Equatorial Mode in a warmer climate

“…The model has been extensively used in climate studies regarding the teleconnections of the Tropical Atlantic (e.g. Martín-Rey et al 2012;Barimalala et al 2012;Kucharski et al 2007Kucharski et al , 2008Kucharski et al , 2009Kucharski et al , 2011Losada et al 2012;Rodriguez-Fonseca et al 2009). Rauscher et al (2011) and Herceg Bulic et al (2012) also argue that SPEEDY can be used in climate change impact studies as it is capable of simulating similar anomalies than those from complex coupled models given the appropriate boundary conditions.…”

The non-stationary influence of the Atlantic and Pacific Niños on North Eastern South American rainfall

“…Although the separated influence of the tropical Atlantic and Pacific oceans on NESA has been documented, to our knowledge there is no work tackling on the stationarity of their relationship with NESA rainfall. Moreover, recent studies have found how the Atlantic and Pacific Niños appear anticorrelated in summer during the decades after the 1970s and at the beginning of the XX century (Polo et al, 2008(Polo et al, , 2015Rodríguez-Fonseca et al, 2009;Martín-Rey et al, 2012, 2014. The concomitant action of both basins on the NESA rainfall region has not been yet explored, although important impacts have been found for the Sahel (Losada et al, 2012;Rodríguez-Fonseca et al, 2015).…”