Ultra High Resolution Global Climate SimulationApril 30, 2013
The problem of predicting climate change and its consequences is motivated by the increasingly urgent need to adapt to near term trends in climate change and the potential changes in the frequency and intensity of extreme events. This project is developing the scientific framework to determine the benefit of employing very-high-resolution global models to investigate regional-scale phenomena. The team will test the hypothesis that higher resolution models are necessary to accomplish the related objectives of 1) the explicit simulation of non-linear phenomena and interactions on the small scale that have feedbacks on large scale climate features; and 2) the accurate and explicit simulation of local to regional scale phenomena, including low-probability, high-impact hydrological events. The focus will be sarigorous evaluation of our hypothesis with high-resolution simulations of observed climate and variability will be the focus. Using a series of stand-alone component and ensemble coupled present-day climate simulations, the project partners will perform comparisons of high- and low-resolution model configurations to determine the potential advantages of high resolution simulations. They will investigate the role of air-sea interaction, the quality of the basic state, and resolution sensitivity on a hierarchy of modes of variability, including the distribution and evolution of extreme events in control, historical, and time-slice experiments of future climate change. An integral component of this project will be the development of new objective diagnostics and metrics to gauge the potential benefit of employing high resolution to improve the representation of regional scale phenomena, especially those related to the hydrological cycle.
The pathway to the project's goals requires an improved understanding of critical sensitivities in model formulation that have been identified from preliminary very-high resolution coupled simulations. Our experimental protocol will enable the project team to investigate these sensitivities, which include the interaction of physics with the choice of dynamical core of the atmospheric model and the initialization of the ocean model, both of which contribute to the development of model biases relative to observations. Implicit on this pathway toward developing a more realistic very-high resolution coupled model for regional projections of climate change will be the exploration of the benefit of very-high resolution contributed by the atmospheric and ocean models, respectively.
Developing a coupled ocean-atmosphere model provides a great challenge to modelers. This challenge is amplified when development is performed at very-high resolution, as scales of variability are resolved that heretofore have not been simulated in coupled mode, and due to the extreme computing that is required to produce such simulations. The climates of these very-high resolution runs each appear relatively stable. Thus, this project will investigate the sources of bias that complicate the simulation of the coupled system, including ocean initialization, parameterized physics and its interaction with the dynamical core. Additionally, the relative influence of high resolution from the atmospheric and ocean models will be explored through combinations of uncoupled and coupled runs in which the resolution of either one or both of the model components is decreased. The enhanced understanding and improved performance that we gain from the initial phase of experimentation will enable the project team to use the very-high resolution coupled model with increased confidence for the investigation of natural variability and anthropogenic forced perturbations in experiments run as part of the World Climate Research Programme's Working Group on Coupled Models Fifth Coupled Model Intercomparison Project (CMIP5) protocol.