Modeling large dust deposition events to alpine snow and their impacts: the role of model resolution

Mineral dust and black carbon (BC) constitute the most important aerosols present in the atmosphere and cryosphere and have well known potential effects on regional and global climate. Upon their deposition they can impact snow albedo, snowpack evolution and timing of snow-melt. However, capturing BC and dust deposition events in mountain regions is currently a challenge due to the complexity of aerosol-cloud interactions and the specifics of mountain meteorological systems, which are difficult to represent in large scale models. Here, we use a case study of dust deposition, between 30 March and 5 April 2018, when a significant dust deposition event was observed within the seasonal snowpack at the Col du Lautaret in the French Alps. This comes in addition to the background BC deposition that occurred during the same period. Specifically, we investigate the role of model resolution in capturing both mountain meteorology, precipitation, and the resulting model predicted dust and BC deposition. For this, the meteorological-chemical model WRF-Chem is used with three nested domains including the primary dust emissions region in Africa (low resolution domain), a second domain that includes Europe, and a third high resolution domain over the Alps. We compare WRF-Chem predicted aerosol and meteorological properties (at different model resolution) with in-situ, remote sensing, and reanalysis products to validate the model and quantify the added value of high resolution modelling within the Alps. We conclude that predicted mountain meteorology including precipitation is significantly better when using the high resolution configuration (3 x 3 km horizontal resolution domain). Additionally, this improved meteorology predicted by the model has significant impacts on predicted dust deposition and BC. The better representation of the mountain meteorology when the resolution becomes finer leads to improved model predicted dust and BC deposition to alpine snow. Implications for this, including improved resolution within models that consider the full aerosol lifecycle in the atmosphere and in snow covered mountain regions is discussed.