Dependence of Warm and Cold Climate Depiction on Climate Model Resolution

Abstract

Climate model results are now being used to asses the potential societal impact of climate change, and to compare with paleoclimate indicators. The models used for these purposes currently employ relatively coarse resolution, and a key question is how the results might change as resolution is improved. To examine this issue, doubled-CO2 and ice age simulations with boundary conditions identical for two different resolutions are run with the GISS model. The resolution dependency of climate change sensitivity, atmospheric dynamics, and regional climate depiction are discussed. The results show that model resolution affects two key processes in the control runs, moist convection and the nonlinear transfer of kinetic energy into the zonal mean flow. The finer resolution model has more penetrative convection but less convection overall, aspects which alter its temperature and wind structure relative to those of the coarser grid model. With finer resolution there are also stronger winds, more evaporation and a more active hydrological cycle. While some of these changes are not particularly, their characteristics are mirrored in the warm and cold climate simulations. In comparison with the coarser resolution model, the finer grid doubled CO2 run has a greater decrease in high-level cloud cover, eddy energy, and eddy energy transports, and a greater increase in atmospheric temperature surface winds, precipitation, and penetrative convection. The ice age finer grid run shows the opposite effect when compared with the medium grid: greater eddy energy and eddy transport increases, greater reduction in hydrologic cycle and atmospheric temperature. Regional climate changes also differ with resolution, due to both the local expression of the different dynamical responses and the differing spatial possibilities. The development of higher resolution models, and the practical use of climate change results, should incorporate an awareness of the potential impact of resolution on model process and climate change depiction.