Coupled Ocean-Atmosphere Modes in the Pacific and Atlantic
Shang-Ping Xie*1, Hideyuki Noguchi*2 and Taroh Matsuno*2
*1 Graduate School of Environmental Earth Science, Hokkaido University
*2 Institute for Global Change Research, Frontier Research System for Global Change
How to characterize the tropical Atlantic sea surface temperature (SST) variability has been highly controversial. Now Tanimoto presents by far the strongest observational evidence in favor of a dipole-and-monopole decomposition (this volume). Here we provide physical basis for such an empirical decomposition and address an important question of why such a latitudinally anti-symmetric dipole mode is not observed in the Pacific.
For this purpose we develop a coupled ocean-atmosphere model that includes both the feedbacks by ocean dynamics and by surface heat flux. Consistent with observations, an interannual equatorial and a decadal dipole modes emerge from the model and are supported by the Bjerknes and a wind-evaporation-SST feedbacks, respectively. The equatorial and dipole modes exhibit distinctive growth curves, with the former peaking at the size of the Pacific Ocean while the latter decreasing monotonically with wavenumber. It thus follows that the equatorial mode will dominate the Pacific whereas it will co-exist with a zonally symmetric dipole mode, a theoretical outcome that explains observations. Such an insight is possible due to our selfconsistent dynamic formulation, in contrast to other ad hoc semi-empirical approaches.
Having emphasized the difference between the oceans in the tropical climate variability, we will present evidence for interaction between extratropical North Atlantic and North Pacific, an inter-oceanic linkage that is particularly pronounced on the decadal time scale.
