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We present a superparameterization of the ECMWF global weather forecasting model OpenIFS with a local, cloud-resolving model. Superparameterization is a multiscale modeling approach used in atmospheric science in which conventional parameterizations of small-scale processes are replaced by local high-resolution models that resolve these processes. Here, we use the Dutch Atmospheric Large Eddy Simulation model (DALES) as the local model. Within a selected region, our setup nests DALES instances within model columns of the global model OpenIFS. This is done so that the global model parameterizations of boundary layer turbulence, cloud physics and convection processes are replaced with tendencies derived from the vertical profiles of the local model. The local models are in turn forced towards the corresponding vertical profiles of the global model, making the model coupling bidirectional. We consistently combine the sequential physics scheme of OpenIFS with the Grabowski superparameterization scheme and achieve concurrent execution of the independent DALES models on separate CPUs. The superparameterized region can be chosen to match the available compute resources, and we have implemented mean-state acceleration to speed up the LES time stepping. The coupling of the components has been implemented in a Python software layer using the OMUSE multi-scale physics framework. As a result, our setup yields a cloud-resolving weather model that displays emergent mesoscale cloud organization and has the potential to improve the representation of clouds and convection processes in OpenIFS. It allows us to study the interaction of boundary layer physics with the large scale dynamics, to assess cloud and convection parameterization in the ECMWF model, and eventually to improve our understanding of cloud feedback in climate models. [Regional superparameterization in a Global Circulation Model using Large Eddy Simulations, Fredrik Jansson, Gijs van den Oord, Inti Pelupessy, Johanna H. Grönqvist, A. Pier Siebesma, Daan Crommelin, Under review (2018)] |
