Modelling sea salt aerosol flux from blowing snow over a changing sea ice environment

A quantitative understanding of climate change in the polar regions being more extreme than at lower latitudes requires monitoring and modelling of key climate variables in these regions. Climate models disagree with observational datasets on the magnitude of the rate of Arctic amplification, and the representation of the chemistry and microphysics of aerosol particles in models is one of the contributing factors to the uncertainty in predicting polar climate. Aerosols represents one of the key model uncertainties through its impact on the surface energy balance via the scattering and absorption of solar radiation, and by its ability to influence cloud microphysics. Sea salt aerosol originating from the sublimation of blowing snow is a newly discovered source of aerosol particles above sea ice during winter and spring, and the hypothesised formation mechanism has been validated recently in the Antarctic. However, the lack of observations over a wide range of sea ice conditions including sub-micron sized particles has been a barrier towards accurately quantifying the mechanism of formation of SSA and the resulting SSA mass flux. Moreover, current blowing snow model parameterisations do not consider the spatial and temporal variability of sea ice and atmospheric state, which has a strong impact on the strength of the particle source from blowing snow across individual storms. In this study, we use observations from the MOSAIC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition (Oct 2019 to Sept 2020) and N-ICE2015 (Feb-June 2015) in the Arctic, and Weddell Sea measurements (June-October 2013) in the Antarctic to better constrain the blowing snow sea salt flux. We consider snow particle size distribution and snow salinity, which are both sensitive model parameters that govern the sea salt aerosol flux over sea ice. A gamma distribution fit is used to characterise the snow particle size distribution as a function of the 10-meter wind speed (ranging from the threshold wind speed (~5ms^-1) to 15ms^-1). Using the observations, we were able to better constrain the shape parameter of the gamma distribution, alpha, when compared to past studies.  We discuss the relationship between snow salinity and snow depth, to capture the influence of the changing sea ice and snowfall on blowing snow aerosol source. We implement these parametrisations derived from point measurements into a chemistry transport model (p-TOMCAT) to better capture the spatially and temporally variable blowing snow source across polar regions, which helps to accurately simulate the aerosol number and mass concentration, and sodium concentration in polar regions.