The effect of SST variability on the midlatitude atmospheric circulation

• Main Authors: Ramesh, H., Li, C., Nummelin, A., Bethke, I.
• Format: Conference Object
• Language: English
• Published: 2023
• Subjects: Pacific; North Atlantic
• Online Access: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5019527

Extratropical SST variability associated with ocean dynamics has well-documented effects on the atmospheric boundary layer, but it is still unclear to what degree and through which mechanisms it influences the free troposphere. The mesoscale features of this SST variability (eddies, fronts) are not captured using typical climate model resolutions, making their large-scale effects difficult to study. We use the Norwegian Earth System Model version 2 (NorESM2) with two ocean setups - standard 1° resolution (MM) and eddy-permitting 0.125° resolution (MX) - both coupled to a 1° atmosphere. With a higher resolution ocean, MX is overall warmer and has different large-scale SST patterns compared to MM. MX exhibits stronger surface turbulent heat fluxes from the ocean to the atmosphere in regions where it is warmer than MM (notably, the western boundary currents, eastern tropical Pacific, and South Atlantic), indicating that SST differences drive the heat flux anomalies. In the extratropical free atmosphere, MX exhibits more energetic storm tracks and a poleward shift of the eddy-driven jets and storm tracks in all sectors and seasons except the North Atlantic during winter. These analyses, together with atmosphere-only experiments forced by SSTs from MX and MM, suggest that the large-scale SST patterns and fine-scale ocean features in an eddy-permitting ocean play a role in setting the jets and storm tracks. Future work will use SST pacemaker experiments to isolate and investigate the underlying coupled mechanisms for how mesoscale ocean variability affects the extratropical atmospheric circulation.