West African Monsoon Dynamics and Eastern Equatorial Atlantic and Pacific SST Anomalies (1970–88)

Abstract

The Laboratoire de Météorologie Dynamique atmospheric GCM is used to investigate relationships between West African monsoon dynamics and SST anomalies in the eastern equatorial Atlantic and Pacific for the period 1970–88. Positive SST anomalies in the eastern equatorial Pacific, mainly associated with a larger east–west divergent circulation over the tropical Atlantic, are found to coincide with negative rainfall anomalies over West Africa. This is the case for the composite ENSO warm episodes of 1972, 1976, 1982, and 1983. By contrast, positive SST anomalies in the eastern equatorial Atlantic are accompanied by a southward shift of the intertropical convergence zone along with negative rainfall anomalies in the Sahel and positive rainfall anomalies in the Guinean region. This was the case in 1987. The ENSO warm event during this year had apparently no significant impact on West African monsoon dynamics. A zonal atmospheric coupling associated with differences of SST anomalies between the eastern equatorial Pacific and the Atlantic is evident in the period 1970–88. Positive (negative) phases of this coupling could enhance the impact of ENSO warm (cold) events on West African monsoon dynamics.

Support for global climate reorganization during the “Medieval Climate Anomaly”

“…9), as seen in observations (e.g. Opoku-Ankomah and Cordery 1994; see also Janicot et al 1998) and ascribed principally to SSTdriven changes in low level humidity (Lamb 1983;Cadet and Nnoli 1987;Vizy and Cook 2002). However, this mechanism does not explain the simulation results because without the adjustment for global average changes (as is done for Figs.…”

A review of droughts on the African continent: a geospatial and long-term perspective

“…Nicholson, 2000). Many studies attempted to investigate the natural causes that could be associated with droughts in Africa (Caminade and Terray, 2010;Dai, 2011Dai, , 2013Giannini et al, 2008Hastenrath et al, 2007;Herweijer and Seager, 2008;Jury et al, 1996;Kerr, 1985;Lebel et al, 2009;Manatsa et al, 2008;Nicholson, 2000;Richard et al, 2001;Shanahan et al, 2009;Tierney et al, 2013;VicenteSerrano, 2012;Zeng, 2003). Some of them also focus on anthropogenic factors, such as climate change, aerosol emissions, land use practices and resulting land-atmosphere interactions, contributing to drought inducing mechanisms (e.g.…”

“…Caminade and Terray (2010) stated that conditions that favour lower summer rainfall in Sahel are when Atlantic Ocean north of equator is cool and south of the equator is warm, El Niño events and increased vertical thermal stability from a warming troposphere. Most of the studies on Sahel droughts concur that the recent severe droughts in Sahel were caused by the ocean warming (southward warming gradient of the Atlantic ocean and steady warming of the Indian Ocean) and a southward shift of inter-tropical convergence zone (ITCZ) (Caminade and Terry, 2010;Dai, 2011;Giannini et al, 2008;Janicot et al, 1998;Kerr, 1985;Lebel et al, 2009;Zeng, 2003). The land-atmosphere feedbacks through natural vegetation and land cover change are also important factors.…”

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

“…These teleconnections are found to be active from intraseasonal to multidecadal timescales (e.g., Lamb and Peppler, 1992;Janicot et al, 1998;Ward, 1998;Giannini et al, 2003;Losada et al, 2010). 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).…”