The effect of improved turbulence parametrization in ICON simulations of Arctic boundary layers

During Arctic winter conditions, turbulent fluxes play a major role in coupling the sea-ice surface with the atmosphere aloft. Since climate models often struggle to accurately model this turbulent exchange in the predominantly stably stratified Arctic boundary layer (BL) it is still a major source of model uncertainty [1]. Therefore, we implemented a new turbulent flux parametrization [2] into ICON-NWP based on observations from the SHEBA campaign in 1997 and evaluate the simulations with observations from the MOSAiC expedition [3]. Results are shown for Pan-Arctic simulations displaying both local and regional effects on the BL.  The new parameterization improves fluxes in very stable situations by strongly reducing turbulent heat fluxes. However, tuning of the diffusion scheme to reduce the flux bias in weakly-stable regime contribute most to the overall model improvement. The reduction of the turbulent heat fluxes led to more realistic BL temperature profiles and stronger sea-ice thickness growth during the winter season. Finally, we assess the impact of the improved turbulence representation in coarser-resolution pan-Arctic ICON simulations over climatological timescales to investigate its relevance for climate applications.

 

This work was supported by the DFG funded Transregio-project TRR 172 “Arctic Amplification (AC)³“.

 

References

 

[1]   A. Solomon, M. Shupe, G. Svensson, N.P.Barton, Y.Batrak: „The winter central Arctic surface energy budget: A model evaluation using observations from the MOSAiC campaign” Elementa – Science of the Anthropocene, Vol.11, 1, (2023), DOI 10.1525/elementa.2022.00104.

[2]   V. Gryanik u. C.Lüpkes, „New Modified and Extended Stability Functions for the Stable Boundary Layer Based on SHEBA and Parametrizations of Bulk Transfer Coefficients for Climate Models“, Journal of Atmospheric Science Vol.77, 8, (2020), DOI 10.1175/JAS-D-19-0255.1.

[3]   Cox J. et al., „Continuous Observations of the Surface Energy Budget and Meteorology over the Arctic Sea Ice during MOSAiC“.