Dust and weather 3000 km apart - the case of February 2021 in Finland

In February 23, 2021, a noticeable amount of Saharan dust was deposited onto snow cover on ground and on sea ice the northern Baltic Sea area and Finland.  Dust was transported in atmosphere during the previous two days quite directly from the northwestern Africa. The deposition occurred mainly due to snow precipitation in the frontal system of a low pressure centre that developed over the Baltic sea. A citizen observation campaign provided samples of dust from Finland during the next days. In this presentation we will address the event from the point of view of high-resolution numerical weather prediction model HARMONIE-AROME and regional atmospheric chemical transport model SILAM. In terms of boundary conditions, these models rely on ECMWF's Integrated Forecast System (IFS) weather data. HARMONIE also imports Copernicus Atmosphere Monitoring Service (CAMS) near-real-time aerosol data, based on IFS-AER.

We will search answer to questions like: How did the atmospheric dynamics influence the dust transport, how did the global and regional models treat this, what are the uncertainties concerning the horizontal and vertical distribution of dust in the models? Can we learn about the impact of the long atmospheric transport to the aerosol properties (size distribution, distribution of species) based on observations, and how well these properties are taken into account by the models? On the other hand, did the dust influence local weather in Finland and how could a local weather model handle the effects? CAMS, SILAM and HARMONIE-AROME estimate aerosol sedimentation on ground - how well this can be validated by the observations?