Global aerosol simulations are conducted by using the Community Atmosphere Model version 5 with the Aerosol Two‐dimensional bin module for foRmation and Aging Simulation version 2 (CAM5‐chem/ATRAS2) ...which was developed in part 1. The model uses a two‐dimensional (2‐D) section representation with 12 size bins from 1 nm to 10 μm and 8 black carbon (BC) mixing state bins, and it can calculate detailed aerosol processes and their interactions with radiation and clouds. The simulations have similar or better agreement with aerosol observations (e.g., aerosol optical depth, absorption aerosol optical depth (AAOD), aerosol number concentrations, mass concentrations of each species) compared with the simulations using the Modal Aerosol Model with three modes. Sensitivity simulations show that global mean AAOD is reduced by 15% by resolving BC mixing state as a result of two competing effects (optical and lifetime effects). AAOD is reduced by 10–50% at low and midlatitudes in the 2‐D sectional simulation because BC absorption enhancement by coating species is reduced by resolving pure BC, thinly coated BC, and BC‐free particles in the model (optical effect). In contrast, AAOD is enhanced by 5–30% at high‐latitudes because BC concentrations are enhanced by 40–200% over the regions by resolving less CCN active particles (lifetime effect). The simulations also suggest a model which resolves more than 3 BC categories (including BC‐free particles) is desirable to calculate the optical and lifetime effects accurately. The complexity of aerosol representation is shown to be especially important for simulations of BC and CCN concentrations and AAOD.
Key Points
Simulations of a 2‐D sectional global aerosol model (CAM5‐chem/ATRAS2) have reasonable agreements with various aerosol measurements
AAOD is enhanced or reduced regionally (5–50%) by improving the representation of optical and lifetime effects of BC mixing state
The complexity of aerosol representation (mixing state and composition) is important for simulations of BC, AAOD, and CCN concentrations
THE COMMUNITY EARTH SYSTEM MODEL Hurrell, James W.; Holland, M. M.; Gent, P. R. ...
Bulletin of the American Meteorological Society,
09/2013, Letnik:
94, Številka:
9
Journal Article
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The Community Earth System Model (CESM) is a flexible and extensible community tool used to investigate a diverse set of Earth system interactions across multiple time and space scales. This global ...coupled model significantly extends its predecessor, the Community Climate System Model, by incorporating new Earth system simulation capabilities. These comprise the ability to simulate biogeochemical cycles, including those of carbon and nitrogen, a variety of atmospheric chemistry options, the Greenland Ice Sheet, and an atmosphere that extends to the lower thermosphere. These and other new model capabilities are enabling investigations into a wide range of pressing scientific questions, providing new foresight into possible future climates and increasing our collective knowledge about the behavior and interactions of the Earth system. Simulations with numerous configurations of the CESM have been provided to phase 5 of the Coupled Model Intercomparison Project (CMIP5) and are being analyzed by the broad community of scientists. Additionally, the model source code and associated documentation are freely available to the scientific community to use for Earth system studies, making it a true community tool. This article describes this Earth system model and its various possible configurations, and highlights a number of its scientific capabilities.
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