Abstract
AbstractThe present assessment of the West African monsoon in the models of the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) indicates little evolution since the third phase of CMIP (CMIP3) in terms of both biases in present-day climate and climate projections.The outlook for precipitation in twenty-first-century coupled simulations exhibits opposite responses between the westernmost and eastern Sahel. The spread in the trend amplitude, however, remains large in both regions. Besides, although all models predict a spring and summer warming of the Sahel that is 10%–50% larger than the global warming, their temperature response ranges from 0 to 7 K.CMIP5 coupled models underestimate the monsoon decadal variability, but SST-imposed simulations succeed in capturing the recent partial recovery of monsoon rainfall. Coupled models still display major SST biases in the equatorial Atlantic, inducing a systematic southward shift of the monsoon. Because of these strong biases, the monsoon is further evaluated in SST-imposed simulations along the 10°W–10°E African Monsoon Multidisciplinary Analysis (AMMA) transect, across a range of time scales ranging from seasonal to intraseasonal and diurnal fluctuations.The comprehensive set of observational data now available allows an in-depth evaluation of the monsoon across those scales, especially through the use of high-frequency outputs provided by some CMIP5 models at selected sites along the AMMA transect. Most models capture many features of the African monsoon with varying degrees of accuracy. In particular, the simulation of the top-of-atmosphere and surface energy balances, in relation with the cloud cover, and the intermittence and diurnal cycle of precipitation demand further work to achieve a reasonable realism.
Highlights
During the second half of the twentieth century, Africa witnessed one of the largest interdecadal climate signals of the recent observational records
We present a comprehensive analysis of the representation of the West African monsoon in the recently available CMIP5 simulations of both presentday and future climates
A robust tendency to warming over the Sahel is noticed, larger by 10%–50% compared to the global warming
Summary
During the second half of the twentieth century, Africa witnessed one of the largest interdecadal climate signals of the recent observational records. VOLUME 26 models of the third phase of the Coupled Model Intercomparison Project (CMIP3; Meehl et al 2007b) used for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), which even disagree on the sign of future rainfall anomalies over the Sahel (e.g., Biasutti and Giannini 2006; Lau et al 2006) This disagreement remains even among models that reasonably simulate the twentieth-century West African climate (Cook and Vizy 2006). Note that the choice of the three averaging domains (Fig. 2) was conveyed by the sign agreement of the precipitation changes (Fig. 1) and some previous works that defined homogeneous regions over the Sahel at interannual to multidecadal time scales (e.g., Ward 1998; Lebel and Ali 2009) For some models, it might not be the most appropriate, in particular for those that do not TABLE 1. Reference http://wiki.csiro.au/confluence/display/ACCESS/ Wu et al (2010) http://esg.bnu.edu.cn/BNU_ESM_webs/htmls/index.html http://www.ec.gc.ca/ccmac-cccma/ Neale et al (2010a); Gent et al (2011) Neale et al (2010b) http://www.cmcc.it/data-models/models Voldoire et al (2013) Rotstayn et al (2010) Hazeleger et al (2010) http://www.lasg.ac.cn/FGOALS/CMIP5 http://www.lasg.ac.cn/FGOALS/CMIP5 Donner et al (2011) Donner et al (2011) http://data.giss.nasa.gov/modelE/ar Collins et al (2008) Volodin et al (2010) Dufresne et al (2013) Dufresne et al (2013) Hourdin et al (2012) Watanabe et al (2010) http://www.mpimet.mpg.de/en/science/models/mpi-esm.html http://www.mpimet.mpg.de/en/science/models/mpi-esm.html Mizuta et al (2012) Mizuta et al (2012) Yokimoto et al (2011) Kirkevag et al (2008)
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