Bibliography - J. Durachta

1. Delworth, T. L., A. J. Broccoli, A. Rosati, R. J. Stouffer, V. Balaji, J. A. Beesley, W. F. Cooke, K. W. Dixon, J. P. Dunne, K. A. Dunne, J. Durachta, and K. L. Findell, et al., 2006: GFDL’s CM2 Global Coupled Climate Models. Part 1: Formulation and Simulation Characteristics. Journal of Climate, 19, doi:10.1175/JCLI3629.1 643-674
   [ Abstract ]

   The formulation and simulation characteristics of two new global coupled climate models developed at NOAA’s Geophysical Fluid Dynamics Laboratory (GFDL) are described. The models were designed to simulate atmospheric and oceanic climate and variability from the diurnal time scale through multicentury climate change, given our computational constraints. In particular, an important goal was to use the same model for both experimental seasonal to interannual forecasting and the study of multicentury global climate change, and this goal has been achieved.
   Two versions of the coupled model are described, called CM2.0 and CM2.1. The versions differ primarily in the dynamical core used in the atmospheric component, along with the cloud tuning and some details of the land and ocean components. For both coupled models, the resolution of the land and atmospheric components is 2° latitude X 2.5° longitude; the atmospheric model has 24 vertical levels. The ocean resolution is 1° in latitude and longitude, with meridional resolution equatorward of 30° becoming progressively finer, such that the meridional resolution is 1/3° at the equator. There are 50 vertical levels in the ocean, with 22 evenly spaced levels within the top 220 m. The ocean component has poles over North America and Eurasia to avoid polar filtering. Neither coupled model employs flux adjustments.
   The control simulations have stable, realistic climates when integrated over multiple centuries. Both models have simulations of ENSO that are substantially improved relative to previous GFDL coupled models. The CM2.0 model has been further evaluated as an ENSO forecast model and has good skill (CM2.1 has not been evaluated as an ENSO forecast model). Generally reduced temperature and salinity biases exist in CM2.1 relative to CM2.0. These reductions are associated with 1) improved simulations of surface wind stress in CM2.1 and associated changes in oceanic gyre circulations; 2) changes in cloud tuning and the land model, both of which act to increase the net surface shortwave radiation in CM2.1, thereby reducing an overall cold bias present in CM2.0; and 3) a reduction of ocean lateral viscosity in the extratropics in CM2.1, which reduces sea ice biases in the North Atlantic.
   Both models have been used to conduct a suite of climate change simulations for the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment report and are able to simulate the main features of the observed warming of the twentieth century. The climate sensitivities of the CM2.0 and CM2.1 models are 2.9 and 3.4 K, respectively. These sensitivities are defined by coupling the atmospheric components of CM2.0 and CM2.1 to a slab ocean model and allowing the model to come into equilibrium with a doubling of atmospheric CO₂. The output from a suite of integrations conducted with these models is freely available online (see http://nomads.gfdl.noaa.gov/).

2. Balaji, V., J. Anderson, I. Held, M. Winton, J. Durachta, S. Malyshev, and R. J. Stouffer, May 2005: The Exchange Grid: a mechanism for data exchange between Earth System components on independent grids. Parallel Computational Fluid Dynamics 2005 - Theory and Applications, Elsevier, http://www.gfdl.noaa.gov/~vb/pdf/xgridpaper.pdf, 179-188
   [ Abstract ]

   We present a mechanism for exchange of quantities between components of a coupled Earth system model, where each component is independently discretized. The exchange grid is formed by overlaying two grids, such that each exchange grid cell has a unique parent cell on each of its antecedent grids. In Earth System models in particular, processes occurring near component surfaces require special surface boundary layer physical processes to be represented on the exchange grid. The exchange grid is thus more than just a stage in a sequence of regridding between component grids. We present the design and use of a 2-dimensional exchange grid on a horizontal planetary surface in the GFDL Flexible Modeling System (FMS), highlighting issues of parallelism and performance.

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