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Idealised Test Cases For Atmospheric Models


Summary

Our researchers have made significant contributions to international weather and climate prediction models used by various agencies around the world. 

Accurate weather and climate forecasts have an important effect on the economy, agriculture, and public safety, ranging from better use of energy reserves to advanced warnings of natural disasters. Central to these forecasts are the use of computer models which in turn rely on accurate numerical methods to solve the corresponding equations. The development of these methods, along with their careful assessment and evaluation, is essential for improving forecasting capabilities and having confidence in the model results. 

Mathematical Sciences Research Group have been working with the National Aeronautics and Space Administration (NASA) to develop forecasting models which led to the development of a new numerical scheme that has been implemented by the part of their GEOS-5 linear model weather and climate prediction model. NASA’s work on global weather and climate predictions is used to inform industry, government and the public in the both the United States and world-wide. 

The Research Group is also creating a worldwide standard for test cases in atmospheric models. Test cases are used by operational centres to evaluate and improve the performance of their models and build confidence in an organisation’s model, making them more prepared to share it. This allows broad benefits to the wider operational modelling community and thus, through improved weather and climate forecasting, to society as a whole. 

USW researchers designed, developed, and implemented a new set of idealised test cases which are used by numerous organisations around the world, including the European Centre for Medium-Range Weather Forecasts (ECMWF) and Deutscher Wetterdienst (DWD). By enhancing their performance and services, USW’s research has also indirectly impacted these groups’ extensive partner organisations and customers worldwide. For example, DWD provide services to numerous organisations including the German Government, private weather forecast agencies, TV stations, as well as more than 20 national weather services worldwide. DWD used the test cases to assess and verify their ICON model giving them, and hence their stakeholders, confidence that the model performs well and produces accurate forecasts. 

The research

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