Geoscience Reference
In-Depth Information
Similarly, a fine surface layer is also found in the ocean (of a depth
ranging from less than 1 m to several meters). It constitutes the top
of the oceanic mixed layer (OML), equivalent to the ABL, where
transfers occur between the surface, with its waves, bubbles and
turbulent structures, to the OML. The OML is the layer where water in
contact with the atmosphere mixes with the cooler layer below. As in
the atmosphere, a stratified transition zone called the thermocline
separates the OML from the deeper layers. This layer is described
more precisely in section 3.2.3.
The ABL is characterized by its temperature, humidity and wind
profiles. The OML is characterised by temperature, salinity and water
currents.
The exchanges between the atmospheric surface layer and upper
ocean (the first few centimeters) are governed by friction, due to the
wind and currents, and by the differences in temperature and the
humidity between them. The thermal conduction, density and thermal
inertia of the atmosphere and ocean are such that turbulent movements
of the atmosphere predominate in the calculation of the turbulent
fluxes: the atmosphere responds almost instantly to variations in
surface temperature, which drives the heat fluxes, and surface currents
are, on average, of an order of magnitude lower than the wind speed.
3.2.2.1. Surface fluxes: above all a problem of atmospheric turbulence
Turbulent fluxes are expressed as the product of the atmosphere
density (assumed to be locally constant), by the covariance of the
vertical speed fluctuations, w ' and of the horizontal wind u' ,
temperature T' , humidity q', depending on the calculated flux:
- momentum flux:
[3.2]
τρ
=
.' '
uw
- sensible heat flux ( C p is the air thermal capacity):
[3.3]
H
=
ρ
.
CwT
.
'
'
p
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