At this point we must introduce the concept of * bulk* or
* profile* models
(the latter are also called * diffusive* or * differential*),
depending
on whether the above equations are vertically integrated through
the layer, or left in their differential form (as above). Bulk
models always presuppose the existence of a mixed layer and
consider the changes of its momentum and heat content due to
entrainment of heat and momentum at the surface and at the bottom
of the mixed-layer. Examples of bulk models are the Niiler Model
[47,7],
and the Garwood model
[21].
The profile-type model
considered here is the Mellor--Yamada model
[43]
with various
degrees of turbulence closure, known as the ``Level 2, 2.5, etc.''
model. For a thorough examination and comparison of several models
of each type the reader is referred to the work of Martin
[40]
and
Kantha and Clayson
[34],
who used meteorological data and
hydrography at several locations around the globe to assess the
performance of each model.