Long-Range Transport of Coarse Mineral Dust Particles: Can a Model Match Observations?

Mineral dust plays a vital role in the Earth system, altering radiative balance, hydrological and carbon cycles, and impacting human health. Particle size is an important factor in these processes. Recent field campaigns reveal unexpected long-range transport of coarse dust particles up to 300 µm from the Sahara across the Atlantic. Current understanding suggests that these particles should be subject to swift gravitational deposition due to their large size and mass. Climate models tend to feature a fine particle bias which results in a bias of the impacts on the Earth system. Longwave radiative heating, for example, is underestimated and shortwave radiative cooling is overestimated at the top of the atmosphere.

Recent aircraft campaigns provide the vertically-resolved dust size distribution evolution from the Sahara to the Caribbean. These are analysed together for the first time. The current Met Office Unified Model dust scheme is then evaluated against the campaign data, to assess its representation of the size distribution evolution and identify areas for improvement. Initial findings show that the deposition rate of coarse particles in the model is too rapid compared to the observations, resulting in an underestimation of dust mass transported from the Sahara. The aim of this work is to fundamentally improve our understanding of mineral dust transport and deposition, as well as to inform the design of the new scheme for the Met Office model.