Time-dependent ventilated thermocline
type: CreativeWork
description: In this thesis, I study the time-varying behavior of a ventila ted thermocline with basin scales at annual and decadal time scales. The variability is forced by three external forcings: the wind stress (chapter 3), the surface heat flux (chapter 4) and the upwelling along the eastern boundary (chapter 5). It is found that the thermocline variability is forced mainly by wind in a shadow zone while m~inly by surface buoyancy flux in a ventilated zone. A two-layer planetary geostrophic model is developed (chapter 2) to simulate a thermocline. The model includes some novel physical mechanisms. Most importantly, it captures the essential feature of subduction; it also is able to account for a time-varying surface temperature. The equation for the interface is a quasi-linear equation, which can be solved analytically by the method of characteristics. The effect of a varying Ekman pumping is investigated. In a shadow zone, it is found that the driving due to the Ekman pumping is mainly balanced by the propagation of planetary waves. However, in a ventilated zone, the cold advection of subducted water plays the essential role in opposing the Ekman pumping. The different dynamics also results in different thermocline variability between the two zones. After a change of Ekman pumping, in the shadow zone, since the baroclinic Ross by wave responds to a changing Ekman pumping slowly (in years to decades), an imbalance arises between the Rossby wave and the Ekman pumping, which then excites thermocline variability. However, in the ventilated zone, both the advection and the Ekman pumping vary rapidly after a barotropic process (about one week) to reach a new steady balance, leaving little thermocline variability. In addition, the evolution of the thermocline and circulation are also discussed. Furthermore, with a periodic Ekman pumping, it is found that linear solutions are approximate the fully nonlinear solution well, particularly for annual forcings. However, the linear distu…
abstract: In this thesis, I study the time-varying behavior of a ventila ted thermocline with basin scales at annual and decadal time scales. The variability is forced by three external forcings: the wind stress (chapter 3), the surface heat flux (chapter 4) and the upwelling along the eastern boundary (chapter 5). It is found that the thermocline variability is forced mainly by wind in a shadow zone while m~inly by surface buoyancy flux in a ventilated zone. A two-layer planetary geostrophic model is developed (chapter 2) to simulate a thermocline. The model includes some novel physical mechanisms. Most importantly, it captures the essential feature of subduction; it also is able to account for a time-varying surface temperature. The equation for the interface is a quasi-linear equation, which can be solved analytically by the method of characteristics. The effect of a varying Ekman pumping is investigated. In a shadow zone, it is found that the driving due to the Ekman pumping is mainly balanced by the propagation of planetary waves. However, in a ventilated zone, the cold advection of subducted water plays the essential role in opposing the Ekman pumping. The different dynamics also results in different thermocline variability between the two zones. After a change of Ekman pumping, in the shadow zone, since the baroclinic Ross by wave responds to a changing Ekman pumping slowly (in years to decades), an imbalance arises between the Rossby wave and the Ekman pumping, which then excites thermocline variability. However, in the ventilated zone, both the advection and the Ekman pumping vary rapidly after a barotropic process (about one week) to reach a new steady balance, leaving little thermocline variability. In addition, the evolution of the thermocline and circulation are also discussed. Furthermore, with a periodic Ekman pumping, it is found that linear solutions are approximate the fully nonlinear solution well, particularly for annual forcings. However, the linear distu…
author: Liu, Zhengyu
language: en_US
keywords: Thermoclines, Ocean-atmosphere interaction
date published: 1991-09
date modified: 2026-07-27T22:05:08Z
provider: Woods Hole Oceanographic Institute
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution

PropertyValue
property ID: Handle
value: https://hdl.handle.net/1912/5492

PropertyValue
property ID: DOI
value: 10.1575/1912/5492