Laboratory Experiments With Abrupt Thermohaline Transitions and Oscillations - Modeling Atmospheric and Oceanic Flows - page 256

and numerical simulations. Hysteresis appears to occupy
a smaller range in experiments that allow more layers of
stratified water in the interior [ Whitehead , 2009]. In the
cavity experiment the hysteresis range is less than the 1%
range of resolution. The experiments uncovered nonlin-
ear self-sustained oscillations that are not reported by box
models and numerical simulations. These new oscillations
exist in the hysteresis range of the layered experiment. The
oscillations represent an excursion back and forth between
layer formation and destruction by mixing so that the tem-
perature, salinity, and flow patterns lie in two different
”climates.”
Double-diffusion processes include salt fingering, layer
formation and flux between layers of two compo-
nents. The two components affect buoyancy and have
different diffusivities such as temperature and salinity
[ Turner , 1973, Schmitt , 1994]. The experiments described
here most strongly indicate that double diffusive heat
and salinity flux is clearly important during layer evo-
lution in a number of the experiments. However, a
close link between abrupt thermohaline changes and
double-diffusion processes is almost completely unex-
plored, even though double diffusion can produce abrupt
transitions ( Veronis , 1965, Whitehead 2002). Experiments
that are designed to clarify the role of double diffusion in
conjunction with abrupt transitions or oscillations would
be valuable. They would form a more complete under-
standing of two-component fluid mechanics.
We are not aware of any existing numerical experiments
that possess no hysteresis with abrupt transitions as in the
cavity experiment. Thus, this issue remains an open area
of research. It is also clear that the manner in which ther-
mohaline flows either oscillate or jump back and forth
between different states as abrupt transitions is still poorly
understood. All these are surprising since both nonlin-
ear oscillations and abrupt transitions are understood
mathematically.

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