Nemo-Nordic 2.0: Operational marine forecast model for the Baltic Sea

• Main Authors: Kärnä, Tuomas, Ljungemyr, Patrik, Falahat, Saeed, Ringgaard, Ida, Axell, Lars, Korabel, Vasily, Murawski, Jens, Maljutenko, Ilja, Lindenthal, Anja, Jandt-Scheelke, Simon, Verjovkina, Svetlana, Lorkowski, Ina, Lagemaa, Priidik, She, Jun, Tuomi, Laura, Nord, Adam, Huess, Vibeke
• Format: Text
• Language: English
• Published: 2021
• Subjects: Sea ice
• Online Access: https://doi.org/10.5194/gmd-2021-101; https://gmd.copernicus.org/preprints/gmd-2021-101/

This paper describes Nemo-Nordic 2.0, an operational marine forecast model for the Baltic Sea. The model is based on the NEMO (Nucleus for European Modelling of the Ocean) circulation model and the previous Nemo-Nordic 1.0 configuration by Hordoir et al. [Geosci. Model Dev., 12, 363–386, 2019]. The most notable updates include the switch from NEMO version 3.6 to 4.0, updated model bathymetry and revised bottom friction formulation. The model domain covers the Baltic and the North Seas with approximately 1 nautical mile resolution. Vertical grid resolution has been increased from 3 to 1 m in the surface layer. In addition, the numerical solver configuration has been revised to reduce artificial mixing to improve the representation of inflow events. Sea-ice is modeled with the SI3 model instead of LIM3. The model is validated against sea level, water temperature and salinity observations, as well as Baltic Sea ice chart data for a two-year hindcast simulation. Sea level root mean square deviation (RMSD) is typically within 10 cm throughout the Baltic basin. Seasonal sea surface temperature variation is well captured, although the model exhibits a negative bias of approximately −0.5 °C. Salinity RMSD is typically below 1.5 g/kg. The model captures the 2014 Major Baltic Inflow event and its propagation to the Gotland Deep. The skill analysis demonstrates that Nemo-Nordic 2.0 can reproduce the hydrographic features of the Baltic Sea.