The thermocline and current structure in subtropical/subpolar basins
Citable URI
http://hdl.handle.net/1912/3100Location
Labrador CurrentNorth Atlantic Current
DOI
10.1575/1912/ 3100Keyword
Thermoclines; Ocean currentsAbstract
Part one of this thesis discusses the structure of the thermocline and the
current pattern within a twolayer model. The corresponding flow field is
explored as the amount of water in the upper layer is gradually reduced (or as
the wind stress is gradually increased).
In the model, when the amount of water in the upper layer is less than a
first critical value, the lower layer outcrops near the middle of the western
boundary. A dynamically consistent picture includes a whole loop of boundary
currents, which surround the outcropping zone completely and have quite
different structures. In addition to the boundary currents found in previous
models, there is an isolated western boundary current (i.e. bounded on one
side by the wall and on the other by a streamline along which the upper layer
thickness vanishes), an internal boundary current and possibly isolated
northern/southern boundary currents. Within the limitations of the twolayer
model, the isolated western boundary current appears to represent the Labrador
Current while the internal boundary current may represent the North Atlantic
Current. A first baroclinic mode of water mass exchange occurs across the ZWCL
(zerowindcurlline).
When the amount of water in the upper layer is less than a second critical
value, the upper layer separates from the eastern wall and becomes a warm
water pool in the southwest corner of the basin. Under this warm water pool
is the ventilated lower layer.
The sea surface density distribution is not specified; it is determined
from a consistent dynamical and mass balance. Implicit in this model is the
assumption that advection dominates in the mixed layer.
The subtropical gyre and the subpolar gyre combine asymmetrically with
respect to the ZWCL.
Chapter I discusses the case when the lower layer depth is infinite.
Chapter II discusses the case when the lower layer depth is finite. In the
Addendum the climatological meaning of this twolayer model is discussed.
Part two of this thesis concerns the use of a continuously stratified
model to represent the thermocline and current structures in
subtropical/subpolar basins. The ideal fluid thermocline equation system Is a
nonlinear, nonstrict hyperbolic system. In an Addendum to Chapter III the
mathematical properties of this equation system are studied and a proper way
of formulating boundary value problems is discussed. Although the equations
are not of standard type, so that no firm conclusions about the existence and
uniqueness of solutions have been drawn, some possible approaches to properly
posed boundary value problem are suggested. Chapter III presents some simple
numerical solutions of the ideal fluid thermocline equation for a subtropical
gyre and a subtropical/subpolar basin using one of these approaches. Our model
predicts the continuous three dimensional thermocline and current structures
in a continuously stratified winddriven ocean. The upper surface density and
Ekman pumping velocity are specified as input data; in addition, the
functional form of the potential vorticity is specified.
The present model emphasizes the idea that the ideal fluid thermocline
model is incomplete. The potential vorticity distribution can not be
determined within this idealized model. This suggests that the diffusion and
upwelling/downwelling within the western boundary current and the outcropping
zone in the northwest corner are important parts of the entire circulation
system.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1984
Collections
Related items
Showing items related by title, author, creator and subject.

Dynamics of the equatorial undercurrent and its termination
Wacongne, Sophie H. C. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 198801)This study focuses on the zonal weakening, eastern termination and seasonal variations of the Atlantic equatorial undercurrent (EUC). The main and most original contribution of the dissertation is a detailed analysis ... 
Shear of small vertical scale observed in the permanent oceanic thermocline
Van Leer, John Cloud (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 197101)Two shear experiments performed in the permanent thermocline are described and analyzed in this thesis. The first employed dye streak techniques to gain fractional meter vertical resolution. Shears with small vertical ... 
Rotating convection driven by differential bottom heating and its application
Park, YoungGyu (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 199609)A convection experiment was done with a rotating rectangular tank as a model of oceanic meridional overturning circulation. Heat flux was fixed at one bottom end of the tank using an electrical heater. Temperature was ...