Variability and predictability of West African monsoon on seasonal and decadal scales

Abstract

Clim Dyn (2016) 47:3391–3392 DOI 10.1007/s00382-016-3429-4 EDITORIAL Variability and predictability of West African monsoon on seasonal and decadal scales Yongkang Xue 1 · Serge Janicot 2 · William K.‑M. Lau 3 Published online: 26 November 2016 © Springer-Verlag Berlin Heidelberg 2016 Recent observational evidence supports the notion that there are strong decadal climate variabilities in the Sahel and sur- rounding areas from the 1950s to the 2000s, not only in pre- cipitation, but also in sea surface temperature (SST), vegeta- tion cover, land use and land cover change (LULCC), and aerosol loading and spatial distributions (Xue et al. 2016; Boone et al. 2016; Gu et al. 2016). In the 2010 Climate Dynamics Special Issue “West African Monsoon and its Modeling,” the skills of general circulation models (GCMs) and regional climate models (RCMs) in properly simulating the West African monsoon (WAM) were extensively evalu- ated, and possible causes that contribute to model deficien- cies were investigated. While these studies provided basic understanding of the seasonal variations of WAM climatol- ogy, understanding of the complex interactions of WAM variability associated with SST, land surface, and aerosol forcings at different scales, particularly with respect to sea- sonal to decadal scale forcing, is still lacking. This special issue “Decadal variability of the West Afri- can monsoon, external surface forcings, and their mode- ling” aims to provide the latest research on the main WAM dynamic and physical processes, model predictability, and possible interactions between the WAM and external forc- ings at seasonal to decadal scales. The main themes of this * Yongkang Xue yxue@geog.ucla.edu Department of Geography, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, USA Laboratoire Atmospheres Milieux Observations Spatiales, Sorbonne-Universites, CNRS-UVSQ-UPMC, Paris, France Earth System Science Interdisciplinary Center, Joint Global Change Research Institute, University of Maryland, College Park, MD, USA special issue are: (1) intercomparison and evaluation of skills of GCMs and RCMs in simulating seasonal and dec- adal variability of WAM rainfall and relevant processes, and its association with SST, LULCC, and aerosol processes, as well as identification of major challenges, deficiencies, and uncertainties that remain in modeling WAM variabil- ity; (2) representations of major WAM characteristics and possible underlying physical and dynamic mechanisms; (3) application of observational and reanalyses data as a path- way for model physics evaluation and improvement, and in understanding the WAM variability; and (4) evaluation of RCM downscaling ability in terms of WAM decadal vari- ability. The papers in the special issue are mainly based on research conducted in conjunction with the second phase of the international West African Monsoon Modeling and Evaluation (WAMME II) project and the African Multidis- ciplinary Monsoon Analysis (AMMA) project. Most papers in this issue are from the WAMME II project focusing on the interactions between the WAM and external forcings. In the WAMME II experiment, realistic but ideal- ized forcings (setting to maximum forcing amplitude) are imposed to examine WAM responses in the WAMME II mod- els. Among them, Xue et al. (2016) investigate relative effects of the global and several major individual ocean basins on the WAM decadal variability and compare the SST’s role and the LULCC effect in initiating and modulating the decadal WAM variability and the 1980s Sahel drought. Boone et al. (2016) use recently available LULCC data to evaluate the sensitiv- ity of WAM seasonal variability to land surface processes and physical mechanisms involved. In addition to multi-model experiments, some of the individual models’ results are also presented. Using the aerosol data from the Goddard Chemis- try Aerosol Radiation and Transport (GOCART) model, Gu et al. (2016) compare aerosol effects over the WAM region and the Asian monsoon regions.