Parameterization Interactions in Global Aquaplanet Simulations
Global climate simulations rely on parameterizations of physical processes that have scales smaller than the resolved ones. In the atmosphere, these parameterizations represent moist convection, boundary layer turbulence and convection, cloud microphysics, longwave and shortwave radiation, and the interaction with the land and ocean surface. These parameterizations can generate different climates involving a wide range of interactions among parameterizations and between the parameterizations and the resolved dynamics. To gain a simplified understanding of a subset of these interactions, we perform aquaplanet simulations with the global version of the Weather Research and Forecasting (WRF) model employing a range (in terms of properties) of moist convection and boundary layer (BL) parameterizations. Significant differences are noted in the simulated precipitation amounts, its partitioning between convective and large-scale precipitation, as well as in the radiative impacts. These differences arise from the way the subcloud physics interacts with convection, both directly and through various pathways involving the large-scale dynamics and the boundary layer, convection, and clouds. A detailed analysis of the profiles of the different tendencies (from the different physical processes) for both potential temperature and water vapor is performed. While different combinations of convection and boundary layer parameterizations can lead to different climates, a key conclusion of this study is that similar climates can be simulated with model versions that are different in terms of the partitioning of the tendencies: the vertically distributed energy and water balances in the tropics can be obtained with significantly different profiles of large-scale, convection, and cloud microphysics tendencies.
Additional Information© 2018 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Received 12 APR 2017; Accepted 10 JAN 2018; Accepted article online 18 JAN 2018; Published online 9 FEB 2018. This work was supported by the Caltech President's and Director's Fund program. The source code for the model used in this study, the WRF V 3.5.1, is freely available at http://www2.mmm.ucar.edu/wrf/users/download/. The input files necessary to reproduce the experiments with WRF as well as the relevant model output are available from the corresponding author upon request (firstname.lastname@example.org). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Part of this research was supported by the U.S. Department of Energy, Office of Biological and Environmental Research, Earth System Modeling. We also acknowledge the support provided by the Office of Naval Research, Marine Meteorology Program, the NASA MAP Program, and the NOAA/CPO MAPP Program.