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What is Scale-adaptive Parameterization?

More information about the research group of Prof. Roel Neggers for Integrated Scale-Adaptive Parameterization and Evaluation (InScAPE) can be found here.

The research group for Integrated Scale-Adaptive Parameterization and Evaluation (InScAPE) of Prof. Roel Neggers aims to develop scale-adaptive parameterizations of small-scale turbulent/convective processes and clouds for larger-scale models, and to constrain those with relevant measurements as obtained from permanent meteorological "supersites".

In General Circulation Models (GCMs) used for numerical weather forecasts and climate prediction, many processes in the atmosphere remain unresolved, due to the limited power and efficiency of present-day supercomputers. These processes include turbulence, convection, clouds and precipitation. As a consequence, their impact on the larger-scale circulation and climate has to be represented by means of parameterization. The evaluation and improvement of such parameterization schemes has been an active research field ever since the start of operational numerical weather forecasting in the middle of the last century.


In recent years however the capacity and speeds of supercomputers have improved rapidly; as a result, resolutions are now feasible at which some previously parameterized processes become, at least partially, resolved. This situation is sometimes referred to as the "grey zone". The consequence is that certain assumptions on which operational, classic parameterizations are based no longer hold. To solve this problem new parameterizations have to be developed that are aware of, and also adaptive to, the scale of both the process they are representing and the grid-spacing of the GCM. This new branch of atmospheric sciences is also known as "scale-adaptive parameterization".

The focus of the research by the InScAPE working group lies on the atmospheric boundary layer. In particular cumulus convection in all its aspects has our interest. The next generation of GCMs that can be expected to become operational within a decade or so all have resolutions at which boundary-layer cumulus becomes partially resolved. Our main goal is therefore to develop a scale-adaptive scheme for moist convective transport and clouds in the boundary layer, for use in such next-generation models. Topics of interest include the size statistics of cumulus cloud populations, cloud overlap, PDF-modelling, and the integration of parameterization of different processes.

The InScAPE group makes use of various research tools. A hierarchy of atmospheric models is used that can be run on platforms ranging from simple workstations to supercomputers (RRZK). The main working horse" model is the Large-Eddy Simulation (LES) model, which simulates the atmospheric flow in a limited domain (25x25x10km) at fine-scale, turbulence and cloud resolving resolutions (25x25x40m). Also included in the hierarchy are regional-domain models and global large-scale models. Although various codes are at our disposal, eventually the new Icosahedral Non-hydrostatic model (ICON) as developed by DWD and MPI-H will be the main model system used in our group. Apart from its innovative triangular grid, ICON has several advantages over existing models; in particular the combination of a non-hydrostatic core with the option of heterogeneous forcing and non-periodic boundaries creates opportunities for research of scale-adaptive paramterizations.

A key ingredient of our set of tools is the so-called "InScAPE Parameterization Testbed". This testbed is an interactiive web-environment in which modelled and observational datastreams come together and can be inter-compared. The aim is to facilitate the parameterization development process, by confronting models with data from idea-inception to finalization. The InScAPE testbed is centered around the Jülich ObservatorY for Cloud Evolution (JOYCE) that is located at the Research Centre Jülich, and is operated by the research group of Prof. Susanne Crewell.