Thermohaline circulation stability : a box model

A thorough analysis of the stability of uncoupled and coupled versions of an inter-hemispheric 3-box model of Thermohaline Circulation (THC) is presented. The model consists of a northern high latitudes box, a tropical box, and a southern high latitudes box, which respectively can be thought as corresponding to the northern, tropical and southern Atlantic ocean. We study how the strength of THC changes when the system undergoes forcings that are analogous to those of global warming conditions. In each class of experiments, we determine, using suitably defined metrics, the boundary dividing the set of forcing scenarios that lead the system to equilibria characterized by a THC pattern similar to the present one, from those that drive the system to equilibria where the THC is reversed. In the case of the uncoupled model, we apply to the equilibrium state perturbations to the moisture and heat fluxes into the three boxes. High rates of increase in the moisture flux into the northern high-latitude box lead to a THC breakdown at smaller total final increases in the moisture flux than low rates, while the presence of moisture flux increases into the southern high-latitude box strongly inhibit the breakdown and can prevent it, in the case of slow rates in the Northern Hemisphere. Similarly, a fast heat flux increases in the North Hemisphere destabilize the system more effectively than slow ones, and again the enhancement of the heat fluxes in the Southern Hemisphere tend to drive the system towards stability. In all cases analyzed slow forcings, if sufficiently weak in the Southern Hemisphere, lead to the reversal of the THC.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Lucarini, Valerio

Advisor dc:contributor.advisor

• Peter H. Stone.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30128

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30128