Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the
degree of Doctor of Science at the Massachusetts Institute of Technology
and the Woods Hole Oceanographic Institution March, 1980
Description:
The Southern Ocean as defined here is the body of water between the
Antarctic Continent and the Antarctic Polar Front, (APF). This ocean is
considered important in the global thermodynamic balance of the
ocean-atmosphere system because large planetary heat losses are believed
to occur at high latitudes. The ocean and atmosphere must transport
heat poleward to balance these losses. In the Southern Hemisphere, the
oceanic contribution to this flux involves a southward transport of heat
across the APF into the Southern Ocean where it is given up to the
atmosphere through air-sea interactions.
In Part I, the air-sea interactions and structure of the near
surface waters of the Southern Ocean are investigated with a three
dimensional time dependent numerical model. The surface waters in this
region in summer are characterized by a relatively warm surface mixed
layer with low salinity. Below this layer, a cold temperature extremum
is usually observed in vertical profiles which is believed to be the
remnant of a deep surface mixed layer produced in winter. The
characteristics of this layer, the surface mixed layer and the observed
distribution of wintertime sea ice are reproduced well by this model.
Unlike some other sea-ice models the air-sea heat exchange is a free
variable. Model estimates of the annual heat loss by the Southern Ocean
exhibit the observed meridional variation of heat gained by the ocean
along the APF with heat lost further south. The model's area average
heat loss is much smaller than that estimated with direct observations.
While several model parameterizations were made which could be in error,
the model results suggest that the Southern Ocean does give up vast
amounts of heat to the atmosphere away from the continental margins.
The model results and direct calculations of air-sea exchanges
suggest a southward heat flux must occur across the APF. The lateral
water mass transition across the front is not discontinuous but occurs
over a finite sized zone of fluid which is dominated by intrusive
finestructure. The characteristics and dynamics of these features are
investigated in Part II to try and assess their importance in the
meridional heat budget.
Observations made on two cruises to the APF are presented and the
space-time scales of the features and thermohaline characteristics are
discussed. It is suggested that double diffusive processes dominated by
salt fingering are active within the intrusions. An extension of
Stern's (1967) model of the stability of a thermohaline front to
intrusive finestructure driven by saltfingering where small scale
viscous processes are included, is presented to explain why intrusions
are observed in frontal zones. The model successfully predicts vertical
scales of intrusions observed in the ocean and the observed dependence
of the intrusions' slopes across density surfaces on the vertical
scale. Since the fastest growing intrusion is not strongly determined
by the model, though, it is likely that finite amplitude effects
determine the dominant scale of interleaving in the ocean.
The analysis predicts that intrusions transport heat, salt and
density down the mean gradients of the front. For the APF, this heat
flux is poleward which is the direction required by the global heat
budget. This model does not describe intrusions at finite amplitude or
in steady state and so cannot be used to estimate the magnitude of the
poleward heat flux due to intrusions in the APF.
Description:
The research reported on here, and my support as a graduate student was provided by the National Science Foundation through grants OCE 75 14056. OCE 76 82036 and OCE 77 28355.
Keywords:
Ocean-atmosphere interaction
;
Ocean temperature
;
Oceanic mixing
;
Heat budget
;
Sea ice
;
Convection
;
Fronts
;
Thomas G. Thompson (Ship) Cruise TN107
;
Knorr (Ship : 1970-) Cruise KN73
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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