Our group use a wide range of numerical models of atmosphere, from regional models to large eddy simulations and single column models.

The Dutch Atmospheric Large-Eddy Simulation (DALES) model is the main LES code employed at InScAPE. A library of prototype cases is used for research and for further code development, including convective cases as well as cases of stratiform clouds. Many of these have been developed within the context of international model intercomparison projects, such as the GCSS boundary layer cloud working group. The library of cases also includes realistic cases at our Testbed locations that are based on a blend of observations and analyses obtained from weather forecast models. The testbed part of our case library spans multiple years at multiple locations of interest.

The current version of DALES ¹⁾ does not incliude a mixed-phase microphysics scheme. To this purpose we are currently working on implementing a full 3-phase microphysics scheme of Seifert-Beheng ²⁾. This code developmen work is supported by the (AC)³ project.

We use the ICON (Icosahedral non-hydrostatic) model in two different version - the LES version ICON-LEM developed during the HDCP2 project and the general circulation model developed by the Max-Planck-Insitute for Meteorology (MPI) and the Germany Weather Service (DWD).

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 ideal opportunities for research of scale-adaptive parameterizations. The setup allows to simulate various synoptic situations at different places and a reasonable comparison to observational data - with this the testbed-situations for parameterization development is growing and getting more variable. For the LES simulations forcing by the COSMO-DE or IFS model is used, which brings the information about the synoptic situation to the outer domain and coarsest resolution. Then the resolution is refined within several nests to actually reach a resolution that is able to resolve large eddies. For simulations around supersites we use at the moment a starting domain of 110km diameter and ca. 600m resolution, then three more nests are included ending with a resolution of ca. 75m (see Figure 1 for a setup around Ny Ålesund).

Figure 1. An impression on the ICON-LEM simulations around the Ny Ålesund meteorological site on Spitsbergen performed by the InScAPE group. The left panels shows the set of nested simulations, while the right panel shows a visualization of clouds and the included topography.

The general circulation model version is used for developing and testing parameterizations. At the moment our focus is on the development and implementation of a PDF cloud scheme. For more information on our development of the PDF cloud scheme, see here; more information about the GCM version of ICON can be found at the MPI website (ICON).

Single Column Modeling (SCM) is a technique in which only a single vertical column from the grid of a GCM is integrated forward in time. The boundary conditions and larger-scale forcings are prescribed, usually obtained from a larger-scale model and/or observations. The suite of subgrid-scale parameterizations of the GCM is free to act, and can create their own unique model state. This can give insight into the behavior of parameterization at process level, and can help in understanding model biases as diagnosed in a GCM.

While the highly reduced cost and enhanced transparency of SCM simulation are clear benefits, one should always be aware of its limitations. For example, the interaction with the larger-scale flow is exclusively one-way (down-scale). However, new techniques are being developed to allow the larger-scale flow to respond to the subgrid physics in SCM simulation. One of these makes use of the Weak Temperature Gradient (WTG) approximation in the tropics.

The InScAPE working group makes use of two SCM codes. One is the ICON-SCM, while the other is the SCM code of the EC-EARTH climate model.