A multi-model approach to the Atlantic Equatorial mode: impact on the West African monsoon

Losada, Teresa; Rodríguez‐Fonseca, Belén; Janicot, Serge; Gervois, Sébastien; Chauvin, Fabrice; Ruti, Paolo

doi:10.1007/s00382-009-0625-5

Cited by 131 publications

(128 citation statements)

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“…in general a good agreement with the timing in the seasonal cycle and its variability. Although the peaks of both, the mean and the variance in the model are delayed by 1 month with respect to the observations, the model seems to be reliable to reproduce the Atlantic Niño seasonality, which is important in terms of tele-connections and impacts (García-Serrano et al, 2008;Losada et al, 2010Losada et al, , 2012. Nevertheless, the model shows an important bias of the annual mean SST over the equatorial region from MAMJ to JASO season ( Figures 1C,D).…”

Section: Description Of the Modelmentioning

confidence: 83%

“…The Atlantic Niño mode is therefore tightly associated with the WAM inter-annual variability (Janicot et al, 1998;Ward, 1998;Giannini et al, 2003;Polo et al, 2008;Losada et al, 2010;Rodriguez-Fonseca et al, 2011;Rodríguez-Fonseca et al, 2015): positive (negative) SST anomalies influence the rainfall over the Gulf of Guinea through a decrease (increase) of the local surface temperature gradient, weakening (strengthening) the monsoon flow and the surface convergence over the Sahel (Vizy and Cook, 2001;Losada et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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Citation:Polo I, Lazar A, Rodriguez-Fonseca B and Mignot J (2015) Tropical Atlantic variability is strongly biased in coupled General Circulation Models (GCM). Most of the models present a mean Sea Surface Temperature (SST) bias pattern that resembles the leading mode of inter-annual SST variability. Thus, understanding the causes of the main mode of variability of the system is crucial. A GCM control simulation with the IPSL-CM4 model as part of the CMIP3 experiment has been analyzed. Mixed layer heat budget decomposition has revealed the processes involved in the origin and development of the leading inter-annual variability mode which is defined over the Equatorial Atlantic (hereafter EA mode). In comparison with the observations, it is found a reversal in the anomalous SST evolution of the EA mode: from west equator to southeast in the simulation, while in the observations is the opposite. Nevertheless, despite the biases over the eastern equator and the African coast in boreal summer, the seasonality of the inter-annual variability is well-reproduced in the model. The triggering of the EA mode is found to be related to vertical entrainment at the equator as well as to upwelling along South African coast. The damping is related to the air-sea heat fluxes and oceanic horizontal terms. As in the observation, this EA mode exerts an impact on the West African and Brazilian rainfall variability. Therefore, the correct simulation of EA amplitude and time evolution is the key for a correct rainfall prediction over tropical Atlantic. In addition to that, identification of processes which are responsible for the tropical Atlantic biases in GCMs is an important element in order to improve the current global prediction systems.

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Section: Description Of the Modelmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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“…Both of them are characterized by an anomalous warming in the east of the basin, associated with a weakening of the climatological trades and supported by the Bjerknes positive feedback (Bjerknes 1969, Zebiak 1993. Although ENSO impacts are larger, both are known to have worldwide impacts (Philander 1990, Losada et al 2010a,b, López-Parages and Rodríguez-Fonseca 2012.…”

Section: Introductionmentioning

confidence: 99%

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

Martín‐Rey¹,

Polo²,

Rodríguez‐Fonseca³

et al. 2012

Sci. Mar.

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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...

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“…For a warming in the Atlantic, some studies show how this dipole is the result of a weakening in the sea level pressure gradient between ocean and land and, hence, in a southward shift of the ITCZ from its climatological position, which translates into more rainfall over Guinea and less rainfall over the Sahel. However, substantial discrepancies in simulating the Atlantic SST effect among AGCM models have been reported in Losada et al (2010). The WAMME models also show quite large discrepancies in simulating Atlantic SST effects: while the GSFC GEOS-5, the MRI/JMA, and the UCLA AGCM show a large impact over West Africa, the ICTP-UMD GCM, the UCLA GFS, and the UCONN CAM5 show reduction in precipitation only over the eastern Sahel and some positive precipitation anomalies over West Africa Fig.…”

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confidence: 99%

West African monsoon decadal variability and surface-related forcings: second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II)

et al. 2016

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in the Sahel climate system at seasonal to decadal scales. The project's strategy is to apply prescribed observationally based anomaly forcing, i.e., "idealized but realistic" forcing, in simulations by climate models. The goal is to assess these forcings' effects in producing/amplifying seasonal and decadal climate variability in the Sahel between the 1950s and the 1980s, which is selected to characterize the great drought period of the last century. This is the first multi-model experiment specifically designed to simultaneously evaluate such relative contributions. The WAMME II models have consistently demonstrated that SST forcing is a major contributor to the twentieth century Sahel drought. Under the influence of the maximum possible SST forcing, the ensemble mean of WAMME II models can produce up to 60 % of the precipitation difference during the period. The present paper also addresses the role of SSTs Abstract The second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II) is designed to improve understanding of the possible roles and feedbacks of sea surface temperature (SST), land use land cover change (LULCC), and aerosols forcings This paper is a contribution to the special issue on West African climate decadal variability and its modeling, consisting of papers from the West African Monsoon Modeling and Evaluation (WAMME) and the African Multidisciplinary Monsoon Analyses (AMMA) projects, and coordinated by Yongkang Xue, Serge Janicot, and William Lau. Provided Funding information has to be tagged. Electronic supplementary materialThe online version of this article (doi:10.1007/s00382-016-3224-2) contains supplementary material, which is available to authorized users. 3in triggering and maintaining the Sahel drought. In this regard, the consensus of WAMME II models is that both Indian and Pacific Ocean SSTs greatly contributed to the drought, with the former producing an anomalous displacement of the Intertropical Convergence Zone before the WAM onset, and the latter mainly contributes to the summer WAM drought. The WAMME II models also show that the impact of LULCC forcing on the Sahel climate system is weaker than that of SST forcing, but still of first order magnitude. According to the results, under LULCC forcing the ensemble mean of WAMME II models can produces about 40 % of the precipitation difference between the 1980s and the 1950s. The role of land surface processes in responding to and amplifying the drought is also identified. The results suggest that catastrophic consequences are likely to occur in the regional Sahel climate when SST anomalies in individual ocean basins and in land conditions combine synergistically to favor drought.Keywords Sahel seasonal and decadal climate variability · Sahel drought, SST and land forcings · GCM

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A multi-model approach to the Atlantic Equatorial mode: impact on the West African monsoon

Cited by 131 publications

References 35 publications

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

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

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

West African monsoon decadal variability and surface-related forcings: second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II)

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