Speaker: Sydney Kramer, Columbia/Lamont
Title: "Modeling the Global Atmospheric Response to Persistent Regional SST Anomalies in the North Atlantic Ocean"
Abstract:
Sea surface temperature (SST) trends in the midlatitudes drive ocean–atmosphere feedbacks with implications for regional and global climate variability. The North Atlantic Warming Hole (NAWH), a cooling trend in the subpolar North Atlantic observed since 1870 despite warming global oceans, forces an atmospheric response that may be important for impacts as well as feedbacks on the NAWH itself. Global atmospheric model experiments demonstrate that the NAWH enhances local wind speeds and surface heat fluxes through interaction with the jet stream, establishing a positive feedback that sustains cold SST anomalies. The latitude of the NAWH has a secondary influence, but proximity to the subpolar jet appears essential. A targeted model intercomparison project involving thirteen atmospheric general circulation model configurations confirms that resolution, vertical stability, and jet representation shape the atmospheric response. The experiments reveal strong sensitivity to model configuration, particularly in simulating NAO-related variability and downstream European hydroclimate, while showing agreement on extratropical SST forcing influencing the tropical Atlantic. A study of the marine heatwave (MHW) appearing since 2012 off the U.S. Mid-Atlantic Coast highlights how warm SST anomalies elicit a distinct and consistent atmospheric response. Similarly designed AGCM experiments show that the warm anomaly produces a low SLP response that produces cyclonic surface winds and associated stress driving changes in Ekman pumping, sea level, and geostrophic currents. Together, these studies identify the key mechanisms by which midlatitude SST anomalies, both warm and cold, interact with the atmosphere to modulate emergent climate signals and some of their impacts.
In person attendance at this seminar is only open to Columbia University affiliates.
