An Investigation On Parametric Sensitivity And Uncertainty In Precipitation And Aerosol Effects Simulated With The Community Atmosphere Model CAM5

In atmosphere sciences, uncertainties are usually related to climate prediction.Quantifying and reducing the uncertainty is a high priority. Despite increased computational power enabling higher resolution, Global Circulation Models(GCMs)still rely on parameterizations to represent the subgrid variability of clouds, aerosols,and their interactions. To investigate the parametric sensitivity and uncertainty in aerosol-cloud-precipitation interactions, two large ensemble simulation are conducted with the Community Atmosphere Model version 5(CAM5), one with perturbed parameters related to cloud process(C-Ensemble), the other with perturbed parameters associated with cloud microphysics and aerosol emissions(A-Ensemble).Both ensemble simulations are used to investigate the sensitivity of precipitation characteristics(mean, extreme, and diurnal cycle) to the uncertain parameters, and only A-Ensemble is used to study aerosol effects(sulfate, black carbon(BC), and dust)on East Asian climate.Results shows that precipitation and aerosol effects on East Asian climate do not always respond monotonically to parameter change; the interactions between parameters are not important at global scale, but are not true at regional or seasonal scale, especially for precipitation; the most important parameters for mean and extreme precipitation are related to deep convection scheme. The parametric uncertainty could not explain the mispresentation of the diurnal cycle of precipitation in midlatitute, indicating that there are structural errors in CAM5. Due to the different optical and microphysical properties and spatial distributions, sulfate, BC, and dust have very different impacts on East Asian Monsoon. The spatial patterns of both sign and magnitude of aerosol-induced changes in radiative fluxes, cloud, and precipitation could be different, depending on the aerosol types, when parameters are sampled in different ranges of values. Some cloud microphysical parameters show significant impacts on aerosol effects on East Asian climate, indicating that the uncertainty in cloud simulation imposes an additional challenge in quantifying aerosol effects.