S2: Improved Parameterizations and Numerics in Climate Models

Principal investigators: Prof. Ulrich Achatz (Goethe University Frankfurt), Dr. Nils Brüggemann (Universität Hamburg), Dr. Sergey Danilov (Alfred Wegener Institute for Polar and Marine Research), Prof. Carsten Eden (Universität Hamburg), Dr. Johann Jungclaus (Max Planck Institute for Meteorology), Dr. Peter Korn (Max Planck Institute for Meteorology)

Based on the work of the first phase of S2 and other subprojects, we will continue in S2 to implement the new and consistent parameterizations and numerical algorithms into the two national climate models: ICON-a/ICON-o and OpenIFS/FESOM2. Together with E3SM (Golaz et al., 2019), the two models developed in Germany are currently the only climate models based on modern, unstructured meshes with the possibility to local refinements, an option which will be used in this CRC as well. We target in this CRC on these two coupled model – both participating in CMIP6 (Eyring et al., 2016a) and other international projects – since they are at the forefront of model development both on global and European scale. As part of the German national climate model development strategy, it is envisioned to push the cooperative development of both models, which is strongly supported by this CRC. Together with subproject S1, where metrics for model performance and energy consistency are developed, S2 will provide an assessment of the effects of improved energetically consistent methods in applications of the coupled ocean and atmosphere models. Three main areas are the focus of S2:

  • ocean parameterizations, atmosphere parameterizations, and numerics.

We will implement extended versions of the gravity wave effect closure IDEMIX in the ocean models FESOMand ICON-o, and we will implement a framework of energy-based parameterizations for submesoscale ocean turbulence. For the atmosphere, we will implement two similar, but complementary gravity wave parameterizations (IDEMIX-a and MS-GWaM) into ICON-a. For the numerics, we will continue the implementation of a generalized vertical coordinate framework (ALE) in FESOM and ICON-o, and continue the work on higher-order advection schemes. The implementation of the new energy-based closures in the atmosphere and ocean models represents an important step towards our goal of energetically consistent coupled climate models.

Schematic of processes assessed in S2.

The project aims to implement new parameterisations and numerical algorithms designed to improve the energetic consistency, and elaborated in the framework of this CRC, in the ocean components of the new generation of Earth System Models that are presently developed in Germany. It will also support the development and implementation of new atmospheric parameterisations. The project will interact with other projects of this CRC providing a framework for the synthesis of the collaborative efforts and serve, together with S1, as a metric for its success.

The AWI climate model

The model consists of the FESOM ocean model coupled to the ECHAM6.3 atmosphere model. Coupled configurations with various ocean grids are available.

  • FESOM offers multi-resolution functionality
  • FESOM works on arbitrary triangular meshes and allows refinements without nesting in the areas of interest
  • ECHAM6-FESOM allows climate studies with a multi-scale ocean

Advanced FESOM configurations allow grids to be locally eddy resolving to simulate variability adequately where it is observed.

Resolution in CORE-II-forced locally eddy-resolving FESOM run.
Simulated velocities (log |u| @ 50m) in CORE-II-forced locally eddy-resolving FESOM run.

The ICON model system

The system consists of newly developed sub-systems for the atmosphere (ICON-a) and the ocean (ICON-o).

  • ICON-a features non-hydrostatic dynamical core in grid point space.
  • ICON-a implemented at the German Weather Service for regional and global weather forecasting.
  • ICON-a applied at MPI-M using different physics packages at resolutions from 2.5 to 160 km.
  • ICON-a LES simulations at 150m resolution in HD(CP)² project
  • ICON-o based on similar grid structure using mimetic discretisation
  • ICON-o applied at MPI-M at resolutions from 10 to 160 km

ICON-o and ICON-a are coupled by the YAC coupler to form the new Max Planck Earth System Model MPI-ESM-2.

Velocities (log |u| @ 200m) in OMIP-forced ICON-o simulations at 10km resolution.
Streamlines and velocities in the Alps from an HD(CP)² ICON-LES simulation.

Implementing new parameterizations and algorithms

A new vertical coordinate frame for our ocean model has the potential to reduce unwanted spurious mixing effects.

Patrick Scholz, Postdoc in S2

I’m Patrick Scholz, Post Doc at Alfred Wegener Institute and work together with Sergey Danilov at Research area S2: “Improved parameterizations and numerics in climate models”. Aim of this project part is to implement new parameterizations and algorithms to improve the energetic consistency in the ocean component of climate models. In particular I will work with the new Finite Volume Sea Ice Ocean Model (FESOM2.0) and start there to implement a new vertical coordinate frame (Arbitrary Lagrangian Eulerian, ALE), based on vertical mesh motion, that has the potential to reduce unwanted spurious mixing effects in the ocean. ALE also allows to combine different versions of vertical coordinates in a single ocean setup, which will also help to broaden the functionality of the model. Further, we will implement new parameterizations of overflows, improved numerical transport algorithms and an energetically consistent parameterization of vertical mixing.

Working with IDEMIX

We will develop a library that simulates the vertical part of IDEMIX independently from general circulation models.

Hannah Kleppin, Former Postdoc in S2

I'm Hannah Kleppin, I recently finished my PhD at the University of Copenhagen under the supervision of Markus Jochum. Until the end of this year I work in the TRR181 in subproject S2 “Improved parameterizations and numerics in climate models”, together with Johann Jungclaus and Carsten Eden. The main goal of subproject S – Synthesis with climate models as metric – is to test parameterizations that are developed in the other subprojects. I will work on implementing IDEMIX – a closure for internal gravity wave mixing in the ocean -  into ICON (MPI) and FESOM (AWI). We will develop a library that simulates the vertical part of IDEMIX independently from the calling GCM (in this case ICON or FESOM). In the long run other vertical mixing parameterizations will be implemented in this library, so that the effects of the different parameterizations on  e.g. biases in the different GCMs can be readily tested and compared.