Aerosols at the Poles: An AeroCom Phase II multi-model evaluation
Maria Sand1, Bjørn H. Samset1, Yves Balkanski2, Susanne Bauer3, Nicolas Bellouin4, Terje K. Berntsen1,5, Huisheng Bian6, Mian Chin7, Thomas Diehl8, Richard Easter9, Steven J. Ghan9, Trond Iversen10, Alf Kirkevåg10, Jean-François Lamarque11, Guangxing Lin9, Xiaohong Liu12, Gan Luo14, Gunnar Myhre1, Twan van Noije14, Joyce E. Penner19, Michael Schulz10, Øyvind Seland10, Ragnhild B. Skeie1, Philip Stier15, Toshihiko Takemura16, Kostas Tsigaridis3, Fangqun Yu13, Kai Zhang17,9, and Hua Zhang181Center for International Climate and Environmental Research – Oslo (CICERO), Oslo, Norway 2Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-sur-Yvette, France 3NASA Goddard Institute for Space Studies and Columbia Earth Institute, New York, NY, USA 4Department of Meteorology, University of Reading, Reading, UK 5Department of Geosciences, University of Oslo, Oslo, Norway 6Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA 7NASA Goddard Space Flight Center, Greenbelt, MD, USA 8Directorate for Sustainable Resources, Joint Research Centre, European Commission, Ispra, Italy 9Pacific Northwest National Laboratory, Richland, WA, USA 10Norwegian Meteorological Institute, Oslo, Norway 11National Center for Atmospheric Research, Boulder, CO, USA 12Department of Atmospheric Science, University of Wyoming, USA 13Atmospheric Sciences Research Center, State University of New York at Albany, New York, USA 14Royal Netherlands Meteorological Institute, De Bilt, The Netherlands 15Department of Physics, University of Oxford, Oxford, UK 16Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan 17Max Planck Institute for Meteorology, Hamburg, Germany 18Laboratory for Climate Studies, National Climate Center, China Meteorological Administration, Beijing, China 19Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
Received: 13 Dec 2016 – Accepted for review: 07 Feb 2017 – Discussion started: 10 Feb 2017
Abstract. Atmospheric aerosols from anthropogenic and natural sources reach the Polar Regions through long-range transport. 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 inter-comparison 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 inter-model 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 (OA), dust and sea-salt. For a subset of models that represent nitrate and secondary organic aerosols (SOA), we document the role of these aerosols at high latitudes. The seasonal dependence of natural and anthropogenic aerosols differs with natural aerosols peaking in the winter (sea-salt) and spring (dust), whereas AOD from anthropogenic aerosols peaks during late spring/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 0.01–0.02. The models have also estimated the shortwave anthropogenic radiative forcing contributions to the direct aerosol effect (DAE) associated with BC and OA from fossil fuel and biofuel (FF), sulfate, SOA, nitrate, and biomass burning from BC and OA emissions combined. The Arctic modeled annual mean DAE is slightly negative (−0.12 W m−2), dominated by a positive BC FF DAE during spring and a negative sulfate DAE during summer. The Antarctic DAE is governed by BC FF. We perform sensitivity experiments with one of the AeroCom models (GISS modelE) to investigate how regional emissions of BC and sulfate and the lifetime of BC influence the Arctic and Antarctic AOD. A doubling of emissions in East Asia, result in a 33 % increase in Arctic AOD of BC. However, radical changes such as reducing the e-folding lifetime by half or doubling it, still fall within the AeroCom model range.
Sand, M., Samset, B. H., Balkanski, Y., Bauer, S., Bellouin, N., Berntsen, T. K., Bian, H., Chin, M., Diehl, T., Easter, R., Ghan, S. J., Iversen, T., Kirkevåg, A., Lamarque, J.-F., Lin, G., Liu, X., Luo, G., Myhre, G., van Noije, T., Penner, J. E., Schulz, M., Seland, Ø., Skeie, R. B., Stier, P., Takemura, T., Tsigaridis, K., Yu, F., Zhang, K., and Zhang, H.: Aerosols at the Poles: An AeroCom Phase II multi-model evaluation, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1120, in review, 2017.