HR: 1340h
AN: A23B-0781    [Abstracts]
TI: Non-normal Amplification of the Thermohaline Circulation
AU: * Zanna, L
EM: zanna@fas.harvard.edu
AF: Dept of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Tziperman, E
EM: eli@eps.harvard.edu
AF: Dept of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Tziperman, E
EM: eli@eps.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford Street , Cambridge, MA 02138 United States
AB: A simple coupled ocean-atmosphere model, continuous in the meridional direction, is used to examine physical mechanisms leading to transient amplification of thermohaline circulation (THC) anomalies. It is found that in a stable regime, in which small perturbations eventually decay, there are optimal initial conditions leading to a dramatic amplification of initial temperature and salinity anomalies in addition to the THC amplification. The maximum amplification is found after about forty years, and the eventual decay is on a centennial time scale. The initial temperature and salinity anomalies are considerably amplified by factors of a few hundreds and twenty, respectively. The initial conditions leading to this amplification are characterized by mutually canceling initial contributions of temperature and salinity anomalies, such that the initial THC anomaly vanishes. The mechanism of amplification is analyzed and found to be the result of an interaction between a few damped (oscillatory and non-oscillatory) modes with decay time scales of twenty to eight hundred years. The amplification mechanism is also found to be distinct from the advective feedback leading to THC instabilities for large fresh water forcing.
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting