Reducing the Uncertainties in Modeling Aerosol-Cloud-Climate Interactions in East Asia (Invited Presentation)

Emissions of aerosols and gas precursors in China have increased substantially over the past three decades with the rapid economic growth. These increases might have serious consequences for the regional and global climate change, air quality degradation and health problem. However, current generation global aerosol-climate models show the large biases in simulating aerosol distribution in China, highlighting the difficulties and complexities of aerosol modeling in this region. In this study, using the NCAR Community Atmosphere Model version 5 (CAM5) with the Modal Aerosol Module (MAM) we investigate several possible factors behind the large aerosol biases in China: (1) aerosol and precursor gas emissions, (2) representation of important aerosol components (e.g., nitrate), and (3) model horizontal resolution.

Using a new technology-based and seasonally-dependent Multi-scale Emission Inventory for China (MEIC) improves the annual mean AOD simulations in eastern China by 12.9% compared with MODIS observations and 14.7% compared with MISR observations, and explains 22%-28% of the AOD low bias simulated with the default IPCC AR5 emission. Incorporating the nitrate aerosol in CAM5 with the MOSAIC scheme further improves the agreement of AOD with MODIS and MISR observations with simulated nitrate burden comparable to that of sulfate especially in winter. With the gradual increase of model resolution from 2°, 1°, 0.5°, to 0.25°, CAM5 is able to capture the finer structure of aerosol distributions and increase the magnitudes of aerosol concentrations due to better resolved collocation between aerosols and clouds important for aerosol wet scavenging.

Implications of the above improvements for aerosol direct and indirect radiative forcings are investigated. Our study suggestions that aerosol effects on East Asian climate could be significantly underestimated with current generation aerosol-climate models. Long-term measurements of aerosol composition and concentrations in different geographical regions of East Asia are urgently needed to guide the future model developments.