Dynamical Self-Organization Processes for NAO
Hongli Ren, University of Hawaii, Honolulu, HI; and F. F. Jin and J. S. Kug
The dynamic self-organizing processes of month-to-seasonal climatic variability of the North Atlantic Oscillation (NAO) are investigated in this study. It is demonstrated that NAO anomalies emerge as the leading climate mode in the northern Atlantic region because the anomalous flow of NAO gain strong self-reinforcement by organizing synoptic eddies in the Atlantic storm track region. Observational evidences show clearly that anomalous flows associated with NAO tend to systematically slant and stretch ubiquitous transient synoptic eddies to generate anomalies in time-mean eddy-vorticity- and eddy energy- fluxes. All these eddy fluxes are preferentially directed to the left-hand side of anomalous flow associated with NAO. Therefore, the eddy vorticity fluxes, for instance, converge into the center of the cyclonic flow, and diverge from the center of the anticyclonic flow of the NAO. The leading mode of eddy-induced time-mean flow tendency resembles NAO mode over the North Atlantic area, providing a significant positive eddy-induced feedback to NAO. This self-organization mechanism for NAO reflects the essential internal dynamic interactions between weather-storm activity and climate variability. The implications of this eddy feedback mechanism in understanding the excitation of NAO by external forcing as well in understanding the air-sea interaction in the Gulf-stream region will be also addressed.
Session 7A, Global dynamics and processes - II
Tuesday, 13 January 2009, 3:30 PM-5:45 PM, Room 129A
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