Stockholm university
Department of Meteorology

Guest seminar, David S. Battisti, University of Washington Seattle, WA, USA

Seminar

Date: Tuesday 2 September 2025

Time: 11.15 – 12.15

Location: C609 Rossbysalen, MISU, Svante Arrhenius väg 16C, 6th floor

Title: Revisiting the large-scale atmospheric response to midlatitude SST anomalies in the North Atlantic: the impact of resolving mesoscale motions.

We investigate the large‐scale atmospheric circulation response to idealized Gulf Stream SST anomalies in Community Atmosphere Model (CAM6) simulations with 14‐km regional grid refinement over the North Atlantic, and compare it to the responses in simulations with 28‐km regional refinement and uniform 111‐km resolution. The highest resolution simulations show a large response of the wintertime North Atlantic Oscillation (NAO) to positive (2°C) SST anomalies in the Gulf Stream: a decrease in SLP of 4 hPa in the North Atlantic and an increase of 2 hPa over the western Mediterranean, representing a seasonal mean NAO shift of +0.4 standard deviations. The lower‐resolution simulations show a weaker response with a different spatial structure. The enhanced large‐scale circulation response results from an increase in resolved vertical motions at the mesoscale and the associated increase in vertical eddy heat and momentum transport in the free troposphere. In response to positive SST anomalies, these processes lead to a stronger and less variable North Atlantic jet, as is characteristic of positive NAO anomalies. Our results suggest that the atmosphere responds differently to midlatitude SST anomalies in high-resolution models than in the models that are typically used for climate studies (e.g., the CMIP6 models). Implications for midlatitude seasonal-to-decadal prediction are discussed. 

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Last updated: August 18, 2025

Source: MISU

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