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A Wind-Induced Thermohaline Circulation Hysteresis and Millennial Variability Regimes
 

Summary: A Wind-Induced Thermohaline Circulation Hysteresis and Millennial
Variability Regimes
YOSEF ASHKENAZY
Solar Energy and Environmental Physics, BIDR, Ben-Gurion University, Midreshet Ben-Gurion, Israel
ELI TZIPERMAN
Department of Earth and Planetary Sciences, and Division of Engineering and Applied Sciences, Harvard University, Cambridge,
Massachusetts
(Manuscript received 29 August 2006, in final form 12 December 2006)
ABSTRACT
The multiple equilibria of the thermohaline circulation (THC: used here in the sense of the meridional
overturning circulation) as function of the surface freshwater flux has been studied intensively following a
Stommel paper from 1961. It is shown here that multistability and hysteresis of the THC also exist when the
wind stress amplitude is varied as a control parameter. Both the Massachusetts Institute of Technology
ocean general circulation model (MITgcm) and a simple three-box model are used to study and explain
different dynamical regimes of the THC and THC variability as a function of the wind stress amplitude.
Starting with active winds and a thermally dominant thermohaline circulation state, the wind stress ampli-
tude is slowly reduced to zero over a time period of 40 000 yr (40 kyr) and then increased again to its initial
value over another 40 kyr. It is found that during the decreasing wind stress phase, the THC remains
thermally dominant until very low wind stress amplitude at which pronounced Dansgaard­Oeschger-like
THC relaxation oscillations are initiated. However, while the wind stress amplitude is increased, these

  

Source: Ashkenazy, Yossi "Yosef" - Department of Solar Energy and Environmental Physics, Jacob Blaustein Institutes for Desert Research,Ben-Gurion University of the Negev
Tziperman, Eli - Departments of Earth and Planetary Sciences & School of Engineering and Applied Sciences, Harvard University

 

Collections: Environmental Management and Restoration Technologies; Environmental Sciences and Ecology; Geosciences; Physics