Abstract:
A state-of-the-art, high-resolution ocean general circulation model is used to estimate the time-dependent global ocean heat transport and investigate its dynamics.
The north-south heat transport is the prime manifestation of the ocean’s role in global
climate, but understanding of its variability has been fragmentary owing to uncertainties in observational analyses, limitations in models, and the lack of a convincing
mechanism. These issues are addressed in this thesis.
Technical problems associated with the forcing and sampling of the model, and
the impact of high-frequency motions are discussed. Numerical schemes are suggested
to remove the inertial energy to prevent aliasing when the model fields are stored for
later analysis.
Globally, the cross-equatorial, seasonal heat transport fluctuations are close to
+4.5 x 1015 watts, the same amplitude as the seasonal, cross-equatorial atmospheric
energy transport. The variability is concentrated within 200 of the equator and dominated by the annual cycle. The majority of it is due to wind-induced current fluctuations in which the time-varying wind drives Ekman layer mass transports that are
compensated by depth-independent return flows. The temperature difference between
the mass transports gives rise to the time-dependent heat transport.
The rectified eddy heat transport is calculated from the model. It is weak in the
central gyres, and strong in the western boundary currents, the Antarctic Circumpolar
Current, and the equatorial region. It is largely confined to the upper 1000 meters
of the ocean. The rotational component of the eddy heat transport is strong in the
oceanic jets, while the divergent component is strongest in the equatorial region and
Antarctic Circumpolar Current. The method of estimating the eddy heat transport
from an eddy diffusivity derived from mixing length arguments and altimetry data,
and the climatological temperature field, is tested and shown not to reproduce the
model’s directly evaluated eddy heat transport. Possible reasons for the discrepancy
are explored.
