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How does increasing horizontal resolution in a global climate model improve the...

Ma, P., P. J. Rasch, M. Wang, H. Wang, S. Ghan, R. Easter, W. Gustafson, X. Liu, Y. Zhang, and H. Ma (2015), How does increasing horizontal resolution in a global climate model improve the simulation of aerosol-cloud interactions?, Geophys. Res. Lett., 42, 5058-5065, doi:10.1002/2015GL064183.

The Community Atmosphere Model Version 5 is run at horizontal grid spacing of 2, 1, 0.5, and 0.25°, with the meteorology nudged toward the Year Of Tropical Convection analysis, and cloud simulators and the collocated A-Train satellite observations are used to explore the resolution dependence of aerosol-cloud interactions. The higher-resolution model produces results that agree better with observations, showing an increase of susceptibility of cloud droplet size, indicating a stronger first aerosol indirect forcing (AIF), and a decrease of susceptibility of precipitation probability, suggesting a weaker second AIF. The resolution sensitivities of AIF are attributed to those of droplet nucleation and precipitation parameterizations. The annual average AIF in the Northern Hemisphere midlatitudes (where most anthropogenic emissions occur) in the 0.25° model is reduced by about 1 W m-2 (-30%) compared to the 2° model, leading to a 0.26 W m-2 reduction (-15%) in the global annual average AIF.

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