Climate Modelling

The ICON model (Zängl et al., 2015) is set up in limited area mode (LAM) over the Arctic region. Simulations are performed for the pan-Arctic at horizontal grid resolutions of 13 km, 6.58 km, and 3.29 km (respectively R3B7, R3B8, and R3B9, following ICON’s grid terminology). Simulation results show the ability of ICON-LAM to represent the observed spatio-temporal structure of the selected moisture intrusion event and its signature in the temperature, humidity, and wind profiles, and in the surface radiation (Bresson et al., 2022). Ongoing research is on MOSAiC-related modeling studies, specifically on atmospheric rivers and surface energy budget processes.

HIRHAM is an atmospheric regional climate model (Christensen et al., 2007), which we apply to the circum-Arctic domain for various studies, e.g. to test the sensitivity of simulations to a modified surface flux parameterization (Schneider et al., 2021) and to evaluate precipitation and snowfall simulations (Viceto et al., 2022; von Lerber et al., 2022). Recently, the model participated in two coordinated Arctic regional climate model evaluation studies (Sedlar et al., 2020; Inoue et al., 2021) as part of Polar CORDEX.

The original ECHAM5’s land-surface-soil scheme has been replaced in HIRHAM by the advanced land model CLM4.5 (Community Land Model version 4) (Matthes et al., 2017). This model is much more complex in its descriptions of vegetation and soil processes than ECHAM5’s inbuilt land component. CLM4.5 have been widely used in modelling permafrost-related processes. It significantly reduces the simulated bias in active layer thickness  and winter soil temperatures, which significantly feed back to the atmospheric circulation. Recently, an update with respect to CLM5 has been started.

HIRHAM-NAOSIM is a coupled regional climate model for the Arctic (Dorn et al., 2019), primarily designed for improving our understanding of key physical processes in atmosphere, sea ice, and ocean, which are involved in interactions that play a major role in the coupled Arctic climate system. On the one hand, we apply the coupled model to analyze regional feedback processes, e.g. between summer sea ice anomalies and atmosphere (Rinke et al., 2019); on the other hand, we use the coupled model as a test bed for adapted parameterizations and process-based evaluation under quasi realistic atmospheric boundary conditions (Jäkel et al., 2019; Yu et al., 2020). Ongoing research in this context is on improved parameterization of processes related to snow on sea ice, open-water leads, and the heat and momentum exchange at the air-ice and ice-ocean interfaces.

The earth system model AWI-CM has been developed at our institute in the framework of the project TORUS (TOwards Regionally focUsed modelling of decadal climate predictionS, funded by BMBF). The model consists in the Finite Element Sea-Ice Ocean Model (FESOM, developed at AWI) coupled to the atmospheric model ECHAM6 (developed at MPI Hamburg). A detailed description of the model is given by Sidorenko et al. (2015). The model has been applied to the study of climate variability in Rackow et al. (2016). By coupling the <link en science climate-sciences atmospheric-physics atmospheric-chemistry.html internal-link>SWIFT fast scheme for simulating the chemistry of stratospheric ozone depletion in polar winter (Wohltmann et al., 2017) to ECHAM6, the atmospheric component of AWI-CM, we obtained an Earth system model which enables the simulation of interactions between the ozone layer and climate. Currently, we are using ECHAM6 and ECHAM6-SWIFT for the study of the role of tropo-stratospheric interactions and of stratospheric ozone for Arctic-midlatitude linkages.

In addition to complex global Earth system models, we developed and applied a hierarchy of global atmospheric models with reduced complexity. These models are quasi-geostrophic three-level models with varying horizontal resolution (e.g., Sempf et al, 2007; Labsch et al., 2015) and simplified physical parameterizations. The models simulate the spatiotemporal evolution of the Northern Hemisphere large-scale atmospheric circulation very well and thus serve as an idealized tool for the study of low-frequency atmospheric variability and atmospheric circulation regime behavior. In a recent study we investigated the role of quasi-geostrophic dynamics for Arctic-mid-latitude circulation linkages, which remains obscure when using comprehensive Earth-system models (Handorf et al., 2017).