06 January 2016

Evaluating a Chemistry-Coupled Regional Climate Model and Its Sensitivity to Ice Nucleation Representation over East Asia

Summary

(same as Pt. 1)

Online-coupled meteorology-chemistry models are essential tools for simulating interactions among gases, aerosols, and clouds that influence air pollution, weather, and climate. Ice nucleation processes can significantly affect climate by changing the microphysical properties of clouds, but their treatment in current models is subject to large uncertainty. A regionalclimate model based on the Weather Research and Forecasting model coupled with the physics suite of Community Atmospheric Model version 5 (referred to as WRF-CAM5) has been developed recently, but evaluation and application have been limited. Researchers at North Carolina State University and the Department of Energy’s Pacific Northwest National Laboratory, applied WRF-CAM5 to East Asia and evaluated its performance in simulating air quality and regional climate. WRF-CAM5 has an overall acceptable performance for major meteorological variables at the surface and in the planetary boundary layer, as well as precipitation, cloud fraction, and downward longwave and shortwave radiation. The model also generally reproduces the observed seasonal variations and the differences between 2006 and 2011. However, they found moderate to large biases for cloud condensation nuclei over oceanic areas, cloud droplet number concentration, cloud liquid and ice water path, cloud optical depth, and cloud forcing, suggesting a need to improve the model treatments for cloud processes, especially droplet and ice nucleation. In part II of the study, they examined model sensitivity to different heterogeneous ice nucleation parameterizations and dust emissions. They compared model simulations using the original heterogeneous ice nucleation parameterization with a recently developed scheme that connects ice nucleation with dust properties. They discovered that different representations of ice nucleation may lead to very different model performances. They found that dust ice nucleation leads to a much higher ice particle number and mass concentrations in the dust source region, which causes significant changes of cloud droplet number concentrations, cloud optical depth, and precipitation. Sensitivity tests also showed that dust particles play a very important role in the radiation budget and cloud formation through both direct and indirect effects over East Asia.

Contact
Jiwen Fan
Acknowledgments

This research was supported by the Office of Science, DOE Regional and Global Climate Modeling Program (DE-SC0006695 at NCSU and KP1703000 at PNNL) and China’s National Basic Research Program (2010CB951803 at NCSU). Simulations were performed on Kraken/Stampede, provided as an Extreme Science and Engineering Discovery Environment (XSEDE) digital service by the Texas Advanced Computing Center (TACC), supported by National Science Foundation grant number OCI-1053575, and Hopper at the National Energy Research Scientific Computing Center (NERSC), supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Thanks are due to Jian He, a graduate student at NCSU, for making some figures. Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830.