Idealised Test Cases For Atmospheric Models

Global climate modelling systems are employed for weather and climate prediction, and these models are made up of many different components. One such component is the atmospheric model, which is comprised of two different parts: the dynamical core and the physical parameterizations. The dynamical core is a fundamental part of the atmospheric model, responsible for capturing the dynamical behaviour of the Earth's atmosphere via numerical integration of the governing fluid dynamics equations. No two dynamical cores are alike, and their individual successes suggest that no perfect model exists. It is important to be able to assess the dynamical core in isolation, to understand whether the numerical methods used are capturing the required phenomena. To this end, a standard set of idealised test cases need to be created. These test cases can then be used by operational centres to evaluate the performance of their model whilst in development, and hence influence key design aspects of their dynamical core. This testing leads to model improvements, and so builds confidence in an organisation’s model so that they are more prepared to share them, thereby having broad benefits to the wider operational modelling community.  

Example Test Case Result

Dr James Kent has been at the forefront of idealised dynamical core testing. He has designed, developed, and implemented idealised test cases that evaluate the performance of atmospheric dynamical cores. He is a co-organiser of the Dynamical Core Model Intercomparison Project (DCMIP), and his test cases have been used by different weather and climate modelling groups, including the Met Office, ECMWF, NCAR, and NASA models. 

Zonal Wind

Related to the dynamical core of an atmospheric model is the linear model. The linear model is a key tool in data assimilation, for example, it is used in 4D-Var data assimilation. Dr Kent has worked with collaborators at NASA to develop their new linear model, constructing and assessing a novel numerical scheme to improve linear tracer transport. The method developed by Kent is now the default option in the GEOS linear model. 


References: 

Kent, J., Jablonowski, C., Whitehead, J. P., and Rood, R. B., (2012): Downscale Cascades in Tracer Transport Test Cases: an Intercomparison of the Dynamical Cores in the Community Atmosphere Model CAM5, Geoscientifc Model Development, 5, 1517-1530. doi: 10.5194/gmd-5-1517-2012

Kent, J.,  Ullrich, P. A., and Jablonowski, C., (2014): Dynamical Core Model Intercomparison Project: Tracer Transport Test Cases, Quarterly Journal of the Royal Meteorological Society, 140, 1279-1293. doi: 10.1002/qj.2208

Holdaway, D. and Kent, J., (2015): Assessing the tangent linear behavior of common tracer transport schemes and their use in a linearized atmospheric general circulation model, Tellus A, 67, 27895, http://dx.doi.org/10.3402/tellusa.v67.27895

Kent, J. and Holdaway, D., (2017): An Idealised Test Case for Assessing the Linearization of Tracer Transport Schemes in NWP Models, Quarterly Journal of the Royal Meteorological Society, 143, 1746-1755. doi: 10.1002/qj.3027

Ullrich, P. A., Jablonowski, C., Kent, J., Lauritzen, P. H., Nair, R., Reed, K. A., Zarzycki, C. M., Hall, D. M., Dazlich, D., Heikes, R., Konor, C., Randall, D., Dubos, T., Meurdesoif, Y., Chen, X., Harris, L., Kühnlein, C., Lee, V., Qaddouri, A., Girard, C., Giorgetta, M., Reinert, D., Klemp, J., Park, S.-H., Skamarock, W., Miura, H., Ohno, T., Yoshida, R., Walko, R., Reinecke, A., and Viner, K, (2017): DCMIP2016: A Review of Non-hydrostatic Dynamical Core Design and Intercomparison of Participating Models, Geosci. Model Dev., 10, 4477-4509. https://doi.org/10.5194/gmd-10-4477-2017

Zarzycki, C. M., Jablonowski, C., Kent, J., Lauritzen, P. H., Nair, R., Reed, K. A., Ullrich, P. A., Hall, D. M., Dazlich, D., Heikes, R., Konor, C., Randall, D., Chen, X., Harris, L., Giorgetta, M., Reinert, D., Kühnlein, C., Walko, R., Lee, V., Qaddouri, A., Tanguay, M., Miura, H., Ohno, T., Yoshida, R.. Park, S-H., Klemp, J., and Skamarock, W., (2019): DCMIP2016: The Splitting Supercell Test Case, Geosci. Model. Dev., 12, 879-892, https://doi.org/10.5194/gmd-12-879-2019