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DYNAMICAL OCEANOGRAPHY
In the chapters 5-10, basic theory of the midlatitude ocean circulation was
presented. The constant density case was considered in chapter 5 followed
by the case where the stratification was uniformly characterized by a typical profile of the buoyancy frequency N (chapter 7). In this chapter, we
relax the restriction of fixed N over the basin by allowing the density to
vary over the whole flow domain. Although these density differences arise
through gradients in temperature and salinity, here we will only consider
the density field itself. The effect of both quantities on the density and
its consequences for the stability of the large-scale flow will be discussed
in chapter 16. In section 13.1 some characteristics of the thermocline are
presented and the mathematical thermocline problem in section 13.2. The
planetary extension of the constant density theory in chapter 5 is subject
of section 13.3 and the planetary extension of two-layer model follows
in section 13.4. In the last section 13.5, the ventilation theory and the
internal boundary layer theory of the thermocline are presented.
13.1. Characteristics of the thermocline
Profiles of potential temperature ϑ, salinity S and potential density σ 0 (cf.
chapter 1) at a station (along the WOCE A16 section) in the North Atlantic near
(21 ◦ W, 26.5 ◦ N) are plotted in the Figs. 13.1a-c. The potential density increases at
depths between 500 and 1500 meter and then quickly approaches its deep sea
value. The region where the largest gradients occur is called the pycnocline
(Fig. 13.1c) and because there are also strong temperature gradients in this region
(Fig. 13.1a), it is also called the thermocline; we will use this terminology below.
The depth of the thermocline is large at midlatitudes and decreases towards the
equator and the poles. This can be seen in a plot of the potential density σ 0 along
the WOCE A16 section (Fig. 13.1d). For this section, potential temperature and
salinity profiles were plotted in Fig. 1.6 (chapter 1).
Horizontal density gradients influence the ocean circulation e.g., through the
thermal wind balance. These partly density driven flows, however, in turn determine the density distribution through advection of heat and salt. The existence
of the thermocline is the net result of the interaction between flow field and the
density field in the ocean and it is therefore a complicated nonlinear problem. It
maybe no surprise that this problem has not been satisfactorily solved up till now.
The central issue discussed in this chapter is the theory attempting to explain the
presence of the thermocline.
DYNAMICAL OCEANOGRAPHY
In the chapters 5-10, basic theory of the midlatitude ocean circulation was
presented. The constant density case was considered in chapter 5 followed
by the case where the stratification was uniformly characterized by a typical profile of the buoyancy frequency N (chapter 7). In this chapter, we
relax the restriction of fixed N over the basin by allowing the density to
vary over the whole flow domain. Although these density differences arise
through gradients in temperature and salinity, here we will only consider
the density field itself. The effect of both quantities on the density and
its consequences for the stability of the large-scale flow will be discussed
in chapter 16. In section 13.1 some characteristics of the thermocline are
presented and the mathematical thermocline problem in section 13.2. The
planetary extension of the constant density theory in chapter 5 is subject
of section 13.3 and the planetary extension of two-layer model follows
in section 13.4. In the last section 13.5, the ventilation theory and the
internal boundary layer theory of the thermocline are presented.
13.1. Characteristics of the thermocline
Profiles of potential temperature ϑ, salinity S and potential density σ 0 (cf.
chapter 1) at a station (along the WOCE A16 section) in the North Atlantic near
(21 ◦ W, 26.5 ◦ N) are plotted in the Figs. 13.1a-c. The potential density increases at
depths between 500 and 1500 meter and then quickly approaches its deep sea
value. The region where the largest gradients occur is called the pycnocline
(Fig. 13.1c) and because there are also strong temperature gradients in this region
(Fig. 13.1a), it is also called the thermocline; we will use this terminology below.
The depth of the thermocline is large at midlatitudes and decreases towards the
equator and the poles. This can be seen in a plot of the potential density σ 0 along
the WOCE A16 section (Fig. 13.1d). For this section, potential temperature and
salinity profiles were plotted in Fig. 1.6 (chapter 1).
Horizontal density gradients influence the ocean circulation e.g., through the
thermal wind balance. These partly density driven flows, however, in turn determine the density distribution through advection of heat and salt. The existence
of the thermocline is the net result of the interaction between flow field and the
density field in the ocean and it is therefore a complicated nonlinear problem. It
maybe no surprise that this problem has not been satisfactorily solved up till now.
The central issue discussed in this chapter is the theory attempting to explain the
presence of the thermocline.