Publication Date:
2022-05-25
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 September 1996
Description:
This thesis addresses the question of how a highly energetic eddy field could be generated
in the interior of the ocean away from the swift boundary currents. The energy
radiation due to the temporal growth of non-trapped (radiating) disturbances in such a
boundary current is thought to be one of the main sources for the described variability.
The problem of stability of an energetic current, such as the Gulf Stream, is formulated.
The study then focuses on the ability of the current to support radiating instabilities
capable of significant penetration into the far-field and their development with time.
The conventional model of the Gulf Stream as a zonal current is extended to allow
the jet axis to make an angle to a latitude circle. The linear stability of such a nonzonal
flow, uniform in the along-jet direction on a beta-plane, is first studied. The stability
computations are performed for piece-wise constant and continuous velocity profiles.
New stability properties of nonzonal jets are discussed. In particular, the destabilizing
effect of the meridional tilt of the jet axis is demonstrated. The radiating properties
of nonzonal currents are found to be very different from those of zonal currents. In
particular, purely zonal flows do not support radiating instabilities, whereas flows with
a meridional component are capable of radiating long and slowly growing waves.
The nonlinear terms are then included in the consideration and the effects of the
nonlinear interactions on the radiating properties of the solution are studied in detail.
For these purposes, the efficient numerical code for solving equation for the QG potential
vorticity with open boundary conditions of Orlanski's type is constructed. The results
show that even fast growing linear solutions, which are trapped during the linear stage of
developement, can radiate energy in the nonlinear regime if the basic current is nonzonal.
The radiation starts as soon as the initial fast exponential growth significantly slows.
The initial trapping of those solutions is caused by their fast temporal growth. The new
mechanism for radiation is related to the nonzonality of a current.
Description:
This work was supported by NSF Grant OCE 9301845.
Keywords:
Ocean currents
;
Ocean circulation
;
Rossby waves
;
Turbulence
;
Eddies
;
Electric conductivity
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
