Project 8 (WP3): Modeling climate change in Western Africa

Project lead: Sophie Bastin

Post-doctoral researcher: Marco Gaetani

Supervision team: Cyrille Flamant, Frederic Hourdin, Sandrine Bony, Pascale Braconnot

Project period: October 2014 – September 2016

West African Monsoon dynamics in CMIP5 idealized simulations: the competitive roles of SST warming and CO2

In this work, the July-to-September (JAS) WAM variability in the period 1979-2008 is studied in AMIP-like simulations (SST-forced) from CMIP5. The individual roles of global SST warming and CO2 concentration increasing are investigated through idealized experiments simulating a 4K warmer SST and a 4x CO2 concentration, respectively. Results show a dry response in Sahel to SST warming, with dryer conditions over western Sahel. On the contrary, wet conditions are observed when CO2 is increased, with the strongest response over central-eastern Sahel. The precipitation changes are associated to modifications in the regional atmospheric circulation: dry (wet) conditions are associated with reduced (increased) convergence in the lower troposphere, a southward (northward) shift of the African Easterly Jet, and a weaker (stronger) Tropical Easterly Jet. The analysis of dynamics aspects reveals that dry conditions are associated to changes in the tropical atmospheric circulation, while wet anomalies are associated to the reinforcement of regional feedbacks. It is highlighted the importance of the comprehension of the competitive actions of SST warming and CO2 increasing for skilful simulations of Sahel precipitation.

Position offer and results (January 2017 update)