Profiling of Saharan dust from the Caribbean to western Africa – Part 2: Shipborne lidar measurements versus forecasts

A unique 4-week ship cruise from Guadeloupe to Cabo Verde in April–May 2013 see part 1, Rittmeister et al. (2017) is used for an in-depth comparison of dust profiles observed with a polarization/Raman lidar aboard the German research vessel Meteor over the remote tropical Atlantic and respective dust forecasts of a regional (SKIRON) and two global atmospheric (dust) transport models (NMMB/BSC-Dust, MACC/CAMS). New options of model–observation comparisons are presented. We analyze how well the modeled fine dust (submicrometer particles) and coarse dust contributions to light extinction and mass concentration match respective lidar observations, and to what extent models, adjusted to aerosol optical thickness observations, are able to reproduce the observed layering and mixing of dust and non-dust (mostly marine) aerosol components over the remote tropical Atlantic. Based on the coherent set of dust profiles at well-defined distances from Africa (without any disturbance by anthropogenic aerosol sources over the ocean), we investigate how accurately the models handle dust removal at distances of 1500 km to more than 5000 km west of the Saharan dust source regions. It was found that (a) dust predictions are of acceptable quality for the first several days after dust emission up to 2000 km west of the African continent, (b) the removal of dust from the atmosphere is too strong for large transport paths in the global models, and (c) the simulated fine-to-coarse dust ratio (in terms of mass concentration and light extinction) is too high in the models compared to the observations. This deviation occurs initially close to the dust sources and then increases with distance from Africa and thus points to an overestimation of fine dust emission in the models.We thank the R/V Meteor team and German Weather Service (DWD) for their support during the cruise M96. We appreciate the effort of AERONET MAN to equip research vessels with sun photometers for atmospheric research. We are grateful to Angela Benedetti (MACC/CAMS model; European Centre for Medium-Range Weather Forecasts, Reading, UK) for all her fruitful comments and suggestion during the initial phase of paper preparation. The SKIRON model operations were supported by the European Commission through the Seventh Framework Programme MARINA platform (Marine Renewable Integrated Application Platform, grant agreement 241402). NMMB/BSC-Dust model simulations were performed in the MareNostrum supercomputer hosted by BSC. Sara Basart and Oriol Jorba acknowledge the CICYT project (CGL2016-75725-R) of the Spanish Government and the AXA Research Fund. The authors also acknowledge support through ACTRIS-2 under grant agreement no. 654109 from the European Union’s Horizon 2020 Research and Innovation Programme.Peer ReviewedPostprint (published version