Stephen Yeager:
Steve has worked in the Oceanography Section of NCAR's Climate and Global Dynamics Laboratory since 1998. He currently co-leads CGD's Earth System Prediction theme, the Earth System Prediction working group of the Community Earth System Model (CESM) project, the World Climate Research Programme's Decadal Climate Prediction Project (DCPP), and the International Laboratory for High Resolution Earth System Prediction (iHESP).
Abstract:
The fundamental mechanisms that explain high subpolar North Atlantic (SPNA) decadal predictability within a particular modeling framework are described. The focus is on the Community Earth System Model (CESM), run in both a historical forced-ocean configuration as well as in a fully coupled configuration initialized from the former. The initialized prediction experiments comprise the CESM Decadal Prediction Large Ensemble (CESM-DPLE)—a 40-member set of retrospective hindcasts documented in Yeager et al. (2018; doi:10.1175/bams-d-17-0098.1). Heat budget analysis confirms the driving role of advective heat convergence in skillful prediction of SPNA upper ocean heat content out to decadal lead times. The key ocean dynamics are topographically-coupled overturning/gyre fluctuations that are geographically centered over the mid-Atlantic ridge (MAR). Long-lasting predictive skill for ocean heat transport can be related to predictable barotropic gyre and sigma-coordinate AMOC circulations, but depth-coordinate AMOC is far less predictable except in the deepest layers. The foundation of ocean memory (and circulation predictive skill) in CESM-DPLE is Labrador Sea Water thickness, which propagates predictably through interior pathways towards the MAR where large anomalies accumulate and persist. Abyssal thickness anomalies drive predictable decadal changes inthe gyre circulation, including changes in sea level gradient and near surface flow, that account for the high predictability of SPNA upper ocean heat content.
Arranged date for the seminar talk: April 19, 2021 at 15:00.