African Dust Reaching Northwestern Europe: A Case Study to Verify Trajectory Calculations

Abstract

An African dust event reaching northwestern Europe has been documented and examined more thoroughly than ever before, using satellite imagery, upper-air soundings, surface observations, X-ray analyses of the dust composition, low-level dust concentration measurements, and objectively calculated air trajectories. This multidisciplinary study has lead to a consistent explanation of a number of initially puzzling observations. The dust case has been used to verify trajectory calculations based upon wind analyses produced at the European Centre for Medium Range Weather Forecasts (ECMWF). The calculations show excellent agreement with the observations: The error in the horizontal displacements turned out to be at most 200 km, while the traveling distance of the dust was at least 3000 km. The upper limit of the error in the vertical displacement is 50 mb, while the total upward displacement of the dust between the boundary layer in northwestern Africa and the dust layer above northwestern Europe 3 days later was about 300 mb. In appendix C, the trajectory model that is used in this case is given and compared to other approaches.