Regional Modeling of Saharan Dust Aerosol (Invited Presentation)

The Sahara desert in northern Africa is the world's largest source of dust aerosol. Dust plays an important role in the Earth climate system due to its impact on solar and thermal radiation and delivery of nutrients into remote ecosytems. Recently the important role of dust in heterogeneous ice formation in couds has been recognized. Regional-scale models help to understand processes involved in dust emission, transport and deposition, and are suited for comparisons with results of field studies like the SAharan Mineral DUst experiment (SAMUM, 2006-2011) that aimed at improving the understanding of Saharan dust properties to reduce uncertainties in estimates of dust radiative forcing, or at understanding of dust deposition in the oceans. Large-scale models that simulate atmospheric mineral dust transport still often show considerable deviations from observations. This can for example be caused by inadequacies in simulated meteorological fields that are used to compute dust emission fluxes. In contrast to global-scale dust models, regional dust models are expected to better reproduce individual dust events due to their higher grid resolution. Still, the representation of dust emission events that are related to precipitation events (haboobs, density currents) is problematic at grid resolutions that require parameterization of wet convection processes. In addition, soil properties in remote desert regions that are required as input parameters into dust emission routines embedded in dust transport models contain considerable uncertainties. A further challenge lies in simulating the mineral composition of dust particles, which is of importance for describing their optical properties and efficiency as ice nuclei in the atmosphere.

An overview about the dust model activities at the Leibniz Institute for Tropospheric Research in Leipzig, Germany will be given. Recent results of Saharan dust simulations with the regional model COSMO-MUSCAT will be presented. The model computes emission, transport, dry and wet deposition of Saharan dust as well as the effect of dust radiative forcing on heating rates, which in turn impacts stability and circulation patterns in regions affected by dust aerosol. Results that were obtained for modelling the long-range transport of dust towards the Caribbean in the framework of the SALTRACE (Saharan Aerosol Long-Range Transport and Aerosol-Cloud Interaction Experiment) field study in summer 2013 will be presented, as well as a case study of Saharan dust transport across Europe in April 2014. During this event the considerable dust amount was suspected to have influenced the atmospheric stability and cloud formation in mid-Europe.