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Towards a Unied Test Case Suite for Global Atmospheric Models Paul A Ullrich 1 , Chris(ane Jablonowski 2 , James Kent 2 , Kevin Reed 3 , Mark Taylor 4 , Peter Lauritzen 5 , Ram Nair 5 1 University of California Davis, 2 University of Michigan, 3 American Geophysical Union Congressional Fellow, 4 Sandia Na(onal Laboratories, 5 Na(onal Center for Atmospheric Research Test Case 2: Non-Hydrostatic Flow Over a Mountain on a Small Planet Test Case 4: Baroclinic Instability The baroclinic instability of test of Jablonowski and Williamson (2008) examines a feature of great importance to midlatitudinal weather. The DCMIP test suite expands on the original test by adding both potential temperature and Ertel’s PV as tracer elds. Since these quantities are preserved under transport, they should be equivalent to their dynamically computed counterparts. The test also provides the option for running on a reduced radius Earth, which leads to non-hydrostatic effects when the radius is reduced by a factor of X = 1000. Further, the DCMIP test suite adds the option for moisture (plus large-scale condensation) and a formulation which works under a full physics parameterization. Test Case 1: Advection Experiments References Test Case 3: Non-Hydrostatic Gravity Waves on a Small Planet Test Case 5: Idealized Tropical Cyclone Test Case 11: Deforma8onal Flow Test Case 12: HadleyLike Circula8on Test Case 13: Flow Over Topography Overview Velocity Field The Dynamical Core Model Intercomparison Project (DCMIP) that was held at the National Center for Atmospheric Research (NCAR) in August 2012 showcased many next- generation atmospheric models. One consequence of this summer school has been the development of a test case suite for intercomparison of dynamical cores. With participation from 18 current and upcoming atmospheric models, these test cases gave us the opportunity to compare and contrast differences in several different numerical formulations. The tests examine a variety of problems, including basic advection in 3D, simulations on a reduced planet at non-hydrostatic scales and tests incorporating basic moist processes and simplied physics. The atmospheric dynamical core is the principal component of Earth system models and is responsible for solving the equations of motion in the global domain. It is widely acknowledged that standardized testing of dynamical cores is very important to verify consistency, accuracy and performance of atmospheric models. However, until recently, only a few test cases have been available for dynamical core intercomparison of model results in both the dry and moist formulations. This test case is a 3D extension of the deformational ow test of Nair et al. (2011). It is a non- divergent ow eld which features fully 3D motion. The ow eld stretches the tracers to thin laments and then reverses so as to return the tracers to their original position. A set of four tracer variables are specied so as to test the ability of the transport scheme to preserve correlations and sharp gradients while also minimizing error norms. • Nair, R.D., and P.H. Lauritzen. "A class of deforma(onal flow test cases for linear transport problems on the sphere." Journal of Computa(onal Physics 229.23 (2010): 88688887. • Jablonowski, C., and D.L. Williamson. "A baroclinic instability test case for atmospheric model dynamical cores." Quarterly Journal of the Royal Meteorological Society 132.621C (2006): 29432975. • Reed, Kevin A., and Chris(ane Jablonowski. "An analy(c vortex ini(aliza(on technique for idealized tropical cyclone studies in AGCMs." Monthly Weather Review 139.2 (2011): 689710. • Schär, C., et al. "A new terrainfollowing ver(cal coordinate formula(on for atmospheric predic(on models." Monthly Weather Review 130.10 (2002): 24592480. • Ullrich PA, Jablonowski C, Kent J, Lauritzen PH, Nair RD, Taylor MA. 2012. Dynamical Core Model Intercomparison Project (DCMIP) Test Case Document, URL hbp://hydracog.fsl. noaa.gov/site_media/docs/DCMIPTestCaseDocument_v1.7.pdf. This Hadley-like circulation tests the accuracy of coupling between the horizontal and vertical transport operators. It features a fully non-divergent 3D ow eld which mimics the mean circulation of the atmosphere. After 12 hours, the ow reverses itself so that error norms can be computed at 24 hours. Since this ow eld and tracer distribution are smooth, the order-of-accuracy of the full 3D transport operator can be measured. This ow eld transports three thin cloud layers over rapidly varying topography. Models with terrain-following coordinates are known to perform poorly on this test due to spurious mixing between model levels. Error norms are computed after one complete rotation. By shrinking the Earth to a radius of 20 kilometers, non-hydrostatic effects are enhanced. This test case examines the ability of a model to simulate a steady ow over a circular Schär-like mountain (Schär 2002). Test 2-1 features background solid body rotation with a maximum velocity of roughly 20 m/s. Test 2-2 uses a vertically sheared ow (between 20 m/s and 80 m/s at the equator) which leads to a wave response of longer wavelength. When running this test, the wave completely encircles the Earth after 36 hours for the uniform solid-body ow and 24 hours for the sheared ow. Again by shrinking the Earth (reduction factor X = 125), non- hydrostatic effects are enhanced. The gravity wave test examines non-hydrostatic gravity waves triggered by a perturbation in the potential temperature eld. The test is run for one hour, immediately prior to the wave completely encircling the globe. If this test is run in a hydrostatic model, the short wavelength features are no longer present. The phase speed of the propagating wave is known analytically, and so can be used to verify model correctness. The idealized tropical cyclone test of Reed and Jablonowski (2011) uses background conditions which are conductive to tropical cyclone development plus a simplied physical parameterization suite which includes large-scale condensation, surface uxes and a boundary layer parameterization. An idealized vortex is placed into the ow which rapidly intensies producing many tropical cyclone-like features. This test case begins to bridge the gap between idealized test cases and more realistic simulations. This test can be run with either the simplied physics suite or with full model physics. Maximum wind speed and minimum pressure are used for model intercomparsion, and to ensure that the model promotes development and does not allow over- intensication.
