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Aerosols at the poles: an AeroCom Phase II multi-model evaluation

Sand, M., B. H. Samset, Y. Balkanski, S. Bauer, N. Bellouin, T. K. Berntsen, H. Bian, M. Chin, T. Diehl, R. Easter, S. Ghan, T. Iversen, A. Kirkevåg, J. Lamarque, G. Lin, X. Liu, G. Luo, G. Myhre, T. van Noije, J. E. Penner, M. Schulz, Ø. Seland, R. B. Skeie, P. Stier, T. Takemura, K. Tsigaridis, F. Yu, K. Zhang, and H. Zhang (2017), Aerosols at the poles: an AeroCom Phase II multi-model evaluation, Atmos. Chem. Phys., 17, 12197-12218, doi:10.5194/acp-17-12197-2017.

Atmospheric aerosols from anthropogenic and natural sources reach the polar regions through long-range transport and affect the local radiation balance. Such transport is, however, poorly constrained in present-day global climate models, and few multi-model evaluations of polar anthropogenic aerosol radiative forcing exist. Here we compare the aerosol optical depth (AOD) at 550 nm from simulations with 16 global aerosol models from the AeroCom Phase II model intercomparison project with available observations at both poles. We show that the annual mean multi-model median is representative of the observations in Arctic, but that the intermodel spread is large. We also document the geographical distribution and seasonal cycle of the AOD for the individual aerosol species: black carbon (BC) from fossil fuel and biomass burning, sulfate, organic aerosols (OAs), dust, and sea-salt. For a subset of models that represent nitrate and secondary organic aerosols (SOAs), we document the role of these aerosols at high latitudes.

The seasonal dependence of natural and anthropogenic aerosols differs with natural aerosols peaking in winter (seasalt) and spring (dust), whereas AOD from anthropogenic aerosols peaks in late spring and summer. The models produce a median annual mean AOD of 0.07 in the Arctic (defined here as north of 60◦ N). The models also predict a noteworthy aerosol transport to the Antarctic (south of 70◦ S) with a resulting AOD varying between 0.01 and 0.02. The

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Modeling Analysis and Prediction Program (MAP)
Atmospheric Composition Modeling and Analysis Program (ACMAP)