On the representation of aerosol activation and its influence on model-derived estimates of the aerosol indirect effect

Journal Article · Wed Jun 06 00:00:00 EDT 2018 · Atmospheric Chemistry and Physics (Online)

DOI:https://doi.org/10.5194/acp-18-7961-2018· OSTI ID:1459998

Rothenberg, Daniel ; Avramov, Alexander; Wang, Chien

Interactions between aerosol particles and clouds contribute a great deal of uncertainty to the scientific community's understanding of anthropogenic climate forcing. Aerosol particles serve as the nucleation sites for cloud droplets, establishing a direct linkage between anthropogenic particulate emissions and clouds in the climate system. To resolve this linkage, the community has developed parameterizations of aerosol activation which can be used in global climate models to interactively predict cloud droplet number concentrations (CDNCs).However, different activation schemes can exhibit different sensitivities to aerosol perturbations in different meteorological or pollution regimes. To assess the impact these different sensitivities have on climate forcing, we have coupled three different core activation schemes and variants with the CESM-MARC (two-Moment, Multi-Modal, Mixing-state-resolving Aerosol model for Research of Climate (MARC) coupled with the National Center for Atmospheric Research's (NCAR) Community Earth System Model (CESM; version 1.2)). Although the model produces a reasonable present-day CDNC climatology when compared with observations regardless of the scheme used, Δ CDNCs between the present and preindustrial era regionally increase by over 100 % in zonal mean when using the most sensitive parameterization. These differences in activation sensitivity maylead to a different evolution of the model meteorology, and ultimately to aspread of over 0.8 W m^-2 in global average shortwave indirect effect (AIE) diagnosed from the model, a range which is as large as the inter-model spread from the AeroCom intercomparison. Model-derived AIE strongly scales with the simulated preindustrial CDNC burden, and those models with the greatest preindustrial CDNC tend to have the smallest AIE,regardless of their Δ CDNC. This suggests that present-day evaluations of aerosol-climate models may not provide useful constraints on the magnitudeof the AIE, which will arise from differences in model estimates of thepreindustrial aerosol and cloud climatology.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: FG02-94ER61937; 1122374; AGS-1339264
• OSTI ID: 1459998
• Alternate ID(s): OSTI ID: 1502420
• Journal Information: Atmospheric Chemistry and Physics (Online), Journal Name: Atmospheric Chemistry and Physics (Online) Vol. 18 Journal Issue: 11; ISSN 1680-7324
• Publisher: Copernicus Publications, EGU
• Country of Publication: Germany
• Language: English

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54 ENVIRONMENTAL SCIENCES