Modeling West African Monsoon Dacadal Variability and Feedbacks: Second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II)
In the SST experiment, in addition to the global SST effect, each ocean's role is also evaluated. To test this, anomalies of SST forcing in each ocean is removed sequentially from the global SST anomalies, which differs from common practice. The preliminary results from most GCMs consistently indicate that SST has a maximum impact on the WAM decadal variability compared with other forcings, and that the effect of the Pacific Ocean is most dominant. The models, however, differ in producing other oceans' contribution to WAM decadal variability. Moreover, the models with specified maximum SST forcing are still unable to produce full Sahel drought. In the LULC change experiment, a newly available land use change map is applied. To reduce the uncertainty in model simulation, a consistent change in the vegetation maps is imposed for each modeling group. The simulated LULC change impact is also substantial, compatible to but less than the SST forcing. In the dust experiment, the direct impact of dust on the radiation budget and its influence to the Sahel rainfall are evaluated using GOCART dust data and are compared with other external forcings. This is the first attempt to use multi-GCMs and RCMs to collectively explore the roles of multiple external forcing in WAM variability. WAMME2's achievement will provide better understanding of relative importance of various forcing and possible feedback mechanisms, complementary to experiments under IPCC, which are focused more on impacts of emission control scenarios, and CORDEX, which is focus on RCM downscaling ability. WAMME also provides a useful prototype multidisciplinary approach for other monsoon regions' researches.