The West African Monsoon Modeling and Evaluation project (WAMME) and its First Model Intercomparison Experiment

International audienceThis paper presents the scientific challenge in West African monsoon (WAM) simulation and discusses the West African Monsoon Modeling and Evaluation project (WAMME) initiative and its approaches to improve WAM simulations. Major scientific highlights from the first WAMME model comparison are the focus of the paper. Based on the first WAMME experiment, the WAMME models' performance is evaluated with precipitation being the major focus. The analyses indicate that the models with specified SST generally have reasonable simulations of the mean spatial distribution of WAM precipitation but largely fail to produce proper daily precipitation frequency distributions. WAMME multi-model ensembles, however, produce excellent WAM precipitation spatial distribution, intensity, and temporal evolution, better than Reanalysis. In addition, the WAMME is the first project consisting of the most state-of-the-art general circulation models (GCMs) and regional climate models (RCMs) to collectively investigate the WAM/external forcing feedbacks. Cases based on the first WAMME experiment are presented to demonstrate scientific challenges for further investigation of WAM, SST, land, and aerosol interactions. The analyses in this article provide a quantitative assessment on model uncertainty, identify main issues in WAM modeling, and provide a good starting point as benchmarks for future studies

Surface Chemistry, Structure, and Electronic Properties from Microns to the Atomic Scale of Axially Doped Semiconductor Nanowires.

Using both synchrotron-based photoemission electron microscopy/spectroscopy and scanning tunneling microscopy/spectroscopy, we obtain a complete picture of the surface composition, morphology, and electronic structure of InP nanowires. Characterization is done at all relevant length scales from micrometer to nanometer. We investigate nanowire surfaces with native oxide and molecular adsorbates resulting from exposure to ambient air. Atomic hydrogen exposure at elevated temperatures which leads to the removal of surface oxides while leaving the crystalline part of the wire intact was also studied. We show how surface chemical composition will seriously influence nanowire electronic properties. However, opposite to, for example, Ge nanowires, water or sulfur molecules adsorbed on the exterior oxidized surfaces are of less relevance. Instead, it is the final few atomic layers of the oxide which plays the most significant role by strongly negatively doping the surface. The InP nanowires in air are rather insensitive to their chemical surroundings in contrast to what is often assumed for nanowires. Our measurements allow us to draw a complete energy diagram depicting both band gap and differences in electron affinity across an axial nanowire p-n junction. Our findings thus give a robust set of quantitative values relating surface chemical composition to specific electronic properties highly relevant for simulating the performance of nanoscale devices