HR: 17:45h
AN: A14B-07    [Abstracts]
TI: Two-way Feedback Interaction Between the Thermohaline and Wind-driven Circulations
AU: * MacMynowski, D G
EM: macmardg@cds.caltech.edu
AF: Control and Dynamical Systems, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Tziperman, E
EM: eli@eps.harvard.edu
AF: Earth and Planetary Sciences Harvard University, 20 Oxford St, Cambridge, MA 02138 United States
AB: The thermohaline circulation (THC) affects the meridional atmospheric temperature gradient and therefore the atmospheric wind and the wind driven ocean circulation. The wind driven circulation (WDC), in turn, affects the THC by the advection of salinity anomalies into deep water formation sites. This paper considers this two way coupling between the WDC and THC, using tools from engineering feedback control. The coupled system is modeled using an enhanced version of the model of Pasquero and Tziperman (2004). For this model, the two way feedback can have a significant effect on the dynamics of the coupled system. For a reasonable choice of parameters, the feedback destabilizes the THC equilibrium for low fresh-water forcing. The dependence of stability on feedback parameters can be rapidly explored using root locus tools, which we introduce and explain. At higher fresh-water forcing, the model exhibits limit cycle behaviour, and describing function analysis is used with partial success to predict the dependence of limit cycle amplitude on feedback parameters. As the fresh water forcing is increased further, the feedback results in a new stable equilibrium instead of the large amplitude limit cycle that develops without feedback. It is expected that the analysis approaches used here may be broadly applicable to the study of feedback interconnections of other climate systems as well.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3220 Nonlinear dynamics
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting