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. Sea salt aerosols (SSA) produced on sea ice surfaces by blowing snow eventsor the lifting of frost flower crystals have been suggested as importantsources of SSA during winter over polar regions. The magnitude and relativecontribution of blowing snow and frost flower SSA sources, however, remainuncertain. In this study, we use 2007–2009 aerosol extinction coefficientsfrom the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrumentonboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation(CALIPSO) satellite and the GEOS-Chem global chemical transport model toconstrain sources of SSA over Arctic and Antarctic sea ice. CALIOP retrievalsshow elevated levels of aerosol extinction coefficients (10–20 Mm −1 )in the lower troposphere (0–2 km) over polar regions during cold months.The standard GEOS-Chem model underestimates the CALIOP extinctioncoefficients by 50 %–70 %. Adding frost flower emissions of SSAfails to explain the CALIOP observations. With blowing snow SSA emissions,the model captures the overall spatial and seasonal variation of CALIOPaerosol extinction coefficients over the polar regions but underestimatesaerosol extinction over Arctic sea ice in fall to early winter andoverestimates winter-to-spring extinction over Antarctic sea ice. We inferthe monthly surface snow salinity on first-year sea ice required to minimizethe discrepancy between CALIOP extinction coefficients and the GEOS-Chemsimulation. The empirically derived snow salinity shows a decreasing trendbetween fall and spring. The optimized blowing snow model with inferred snowsalinities generally agrees with CALIOP extinctioncoefficients to within 10 % oversea ice but underestimates them over the regions where frost flowers areexpected to have a large influence. Frost flowers could thus contributeindirectly to SSA production by increasing the local surface snow salinityand, therefore, the SSA production from blowing snow. We carry out a casestudy of an Arctic blowing snow SSA feature predicted by GEOS-Chem andsampled by CALIOP. Using back trajectories, we link this feature to a blowingsnow event that occurred 2 days earlier over first-year sea ice and was alsodetected by CALIOP.

Using CALIOP to constrain blowing snow emissions of sea salt aerosols over Arctic and Antarctic sea ice