A Region-wide Characterization of Arctic Aerosol Seasonality and Investigation of Model Departures from Observations

The Arctic shows a warming trend more than twice that of the global average, with a maximum signal in boreal winter. In 2019, aerosols contributed an estimated -1.1 Wm^-2 to the global energy budget, offsetting more than half of the anthropogenic CO2 forcing. In situ observations of Arctic aerosol have long shown a pronounced seasonal cycle—during the so-called "Arctic Haze" event, late Winter/early Spring aerosol concentrations at some stations can be as much as 10-20 times greater than during their late-summer minima. However, data over much of the region remains sparse; observations from passive satellite sensors are largely restricted to summer, and models frequently fail to replicate the seasonality observed at stations. As aerosol forcing in the Arctic is modulated by seasonal changes in solar insolation, Arctic aerosol seasonality remains an important source of uncertainty in the regional energy budget. Using extinction measures from station data and aerosol optical depth (AOD) from the Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instrument, we will characterize the seasonality of aerosol burdens throughout the region, including seasonal trends in AOD, and departures of AerChemMIP model data from observations.