Seminar Announcement “On The Origins, Dynamics, And Predictive Power Of Large-Scale, Low-Frequency Variations In North Atlantic Circulation” By Steve Yeager

There is an upcoming seminar at The University of Colorado which provides further information on what is currently achievable in terms of long term climate system forecasts; see also

Guest Post Titled “Decadal Prediction Skill In A Multi-Model Ensemble” By Geert Jan van Oldenborgh, Francisco J. Doblas-Reyes, Bert Wouters, Wilco Hazeleger

The seminar is the Comprehensive Eaxm of Steve Yaeger [highlight added]. We need more such studies.

COMPREHENSIVE EXAM II – Steve Yeager

DATE and TIME: Monday, March 19, 2012 at 9:00am LOCATION: ATOC Conference Room, Folsom Stadium 255-12 (see directions below)

TITLE:  “On the origins, dynamics, and predictive power of large-scale, low-frequency variations in North Atlantic circulation”

ABSTRACT:

An ensemble of initialized decadal prediction (DP) experiments using the Community Climate System Model, version 4 (CCSM4) shows significant skill at forecasting changes in North Atlantic upper ocean heat content and surface temperature up to a decade in advance.  Coupled model ensembles integrated forward from 10 different start dates spanning 1961 to 2006 with ocean and sea-ice initial conditions obtained from a forced historical experiment (CORE-IA) are found to exhibit a good correspondence with late 20th century ocean observations from the North Atlantic subpolar gyre (SPG) region.   A budget of SPG heat content from the CORE-IA experiment demonstrates the extent to which low-frequency changes in ocean heat advection related to the Atlantic meridional overturning circulation (AMOC) dominated temperature tendencies in this region over the latter half of the 20th century.  Heat budgets computed from the DP ensembles reveal that large advective heat flux anomalies from the  south are highly correlated with those from CORE-IA, and thus the skill of the CCSM4 decadal prediction system in the SPG region is attributable to correct initialization of large-scale ocean circulation anomalies.  These results lend support to the hypothesis that improved AMOC prediction could greatly extend the lead time for skillful prediction of North Atlantic SST and associated climate variations.

However, advances in decadal prediction will require a deeper understanding of the mechanisms which drive low-frequency AMOC variations in general circulation models; the sensitivity of these mechanisms to the model mean state and to sub-gridscale processes which may or may not be parameterized; and the overall fidelity of model-simulated behavior to that found in nature.  Towards that end, a vorticity diagnostics tool has been developed to facilitate the analysis of CCSM4 ocean model output.  The tool is applied here to the CORE-IAsolution, as well as to two companion hindcasts which isolate the buoyancy- and wind-driven components of surface forcing, in order to elucidate the  ocean dynamical response to historical forcings. The mean vorticity balance of the CORE-IA control reveals the key role played by flow-bathymetry interactions in setting the strengths of the Atlantic MOC and subpolar gyre circulation and the location of the North Atlantic current, in the POP model.

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