How Long is the Memory of Tropical Ocean Dynamics

Details How Long is the Memory of Tropical Ocean Dynamics How Long is the Memory of Tropical Ocean Dynamics

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmos21c..08l&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #OS21C-08

Physics

1620 Climate Dynamics (3309), 1635 Oceans (4203), 4215 Climate And Interannual Variability (3309), 4231 Equatorial Oceanography

Scientific paper

Combining classical equatorial wave dynamics and mid-latitude wave dynamics, a unified view is proposed to account for the memory of tropical ocean dynamics in terms of oceanic basin modes. It is shown that the dynamic memory of the ocean is determined by the gravest extratropical planetary wave basin (PB) mode that has the cross-basin time of planetary waves along the poleward basin boundary. For realistic ocean basins, this memory originates from the mid- and high latitude processes and is usually at interdecadal time scales. Because of the important role of the PB modes in the oceanic interdecadal variability, we studied the formation mechanism of the PB modes in a tropical-extratropical basin. These modes are identified numerically by solving an eigenvalue problem of a linear shallow water system. They are the least damped modes in a sense that damping rates are much smaller than eigenfrequencies, suggesting that these modes could easily become sustained under external forcing or air-sea coupling. However, numerically the PB modes can be shut off by applying sponge boundary (the region with extra-heavy damping coefficient) on any side of western, eastern and equatorial boundaries. If the western or eastern boundary is only partially sponged, the gravest PB mode has the time scale determined by the transit time of the planetary wave on the effective latitude (defined as the latitude of the southern tip of the sponge region) instead of the poleward basin boundary, and it exhibits a basin-scale structure with the largest amplitude in the northwest corner of effective basin (defined as the basin between the effective latitude and the equatorward basin boundary) instead of geographic basin. We also found that the Kelvin waves (except those on the northern boundary) are vital to the formation of the periodically oscillating PB modes.

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