measurements; both give information about the broad outlines of
the thermohaline circulation. The thermohaline circulation is
characterized by extremely small velocities (especially vertical
velocity), so direct measurement of the THC is impossible.
Analytic and numerical models have therefore played a major role
in our approach to understanding the THC. In particular, simple
three-dimensional coarse-resolution sector models of the
dynamics of the THC forced by steady mixed-boundary conditions
(pioneered by F. Bryan, 1986a, 1986b) have begun to contribute a
great deal to our understanding of the mean and variable THC.
Sector models contain the rudimentary dynamics needed to model
the THC and its variability in a simplified context that allows
many numerical experiments to be performed. On the other hand,
the applicability of these simplified-model results to the real
ocean will always be in question until they have been confirmed
by experiments using more complex models with higher resolution,
realistic geogr