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Abstract

Several advanced treatments to the representations of aerosols and cloud-aerosol interactions have been implemented in E3SMv1, including emissions, new aerosol particle formation, explicit aging of carbonaceous aerosol species, wet scavenging processes, ice nucleation, and deposition of light-absorbing particles to snowpack and sea ice, which have led to better simulations of aerosol spatial distributions and global impact, compared to the original model (E3SMv0/CESM1.3). Some of the treatments, however, also gave a strong regional radiative cooling. On the other hand, E3SMv1 neglects or crudely treats a few aerosol components that will be increasingly important in future climate and/or play an important biogeochemical role. Nitrate aerosol is projected to become a significant aerosol component as sulfur and carbonaceous emissions are reduced while NO_x and ammonia emissions continue to increase. Advanced aerosol model such as MOSAIC (Zaveri et al., 2008) is needed for the treatment of nitrate and other semi-volatile aerosol species. Global volcanic eruption emissions and stratospheric aerosols are crudely treated in E3SMv1 by prescribing stratospheric aerosol optical properties. A prognostic capability for simulating the eruption emissions and resulting stratospheric sulfate aerosol (Mills et al. 2016) is desirable. Other aerosol species such as secondary organic aerosol (SOA) and light-absorbing organic carbon (a.k.a. brown carbon) have also been neglected or treated very simply in E3SMv1. It has been shown that explicit treatments of gas- and particle-phase chemical oxidation of SOA result in a much better agreement with global measurements (Shrivastava et al. 2015).  E3SMv1 has an unrealistically short lifetime for dust particles. A more sophisticated dust emission scheme (Kok et al., 2014) and a newer size-resolved dry deposition scheme (Petroff and Zhang 2010) can be helpful. Atmospheric dust is also a major supplier of iron and phosphorus nutrients to open ocean and terrestrial ecosystems. Ideally, atmospheric dust cycle should be coupled with ocean biogeochemistry cycle. We propose a series of science-driven model improvements and developments related to the representation of aerosols and snow/ice impurities to better capture their role in the Earth’s water cycle, biogeochemistry, and cryosphere system.

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