Chapter 7: APPLICATIONS
molecular sublayers at the free ocean surface and at a rigid wall may not be
complete. Here, we explore only the application of the surface renewal
approach for modeling the interfacial component of gas exchange.
The renewal of the ocean surface water can occur because of convective,
shear or surface wave instabilities. Portions of fluid are ejected from the
molecular boundary layers into deeper layers, thus providing the renewal of
the surface water. The renewal rate therefore determines the interfacial
fluxes. Csanady (1990) linked the surface renewal with the presence of flow
convergences. The surface convergence zones are usually relatively narrow
and quasi-periodic in space and/or time. The so-called “rollers” (or microscale wave breakings) provide maximum flow convergence.
Modeling surface renewal is based on the relationships connecting the
renewal rate to the environmental parameters such as friction velocity, heat
fluxes etc. Surface films can influence the surface renewal process,
especially under low wind speed conditions (Frew, 1997).
The thermal molecular sublayer of the ocean (cool skin) does not
substantially influence the heat exchange between ocean and atmosphere
except in some extreme conditions (Paulson and Simpson, 1981). At the
same time, air-sea gas transport does substantially depend on parameters of
the oceanic diffusion sublayer. Due to low gas diffusivity in water compared
to the rather high gas diffusivity in air, the diffusion sublayer provides the
main resistance to the interfacial atmosphere-ocean gas transport (Bolin,
1960).
Despite different roles in the heat and gas exchange at the air-sea
interface, the thermal and diffusion sublayers are governed by similar laws.
Soloviev and
(1994) proposed relating the temperature difference
across the thermal sublayer (cool skin of the ocean), 'T, to the interfacial
(direct) gas transfer velocity (K t ) (Section 2.3). The more readily available
cool skin data are then used for an adjustment of the gas transfer
parameterization. A further extension of the renewal model includes the
effects of solar radiation and rainfall on the molecular boundary layers
(Sections 2.4 and 2.5).
Jaehne et al. (1987) proposed the controlled heat flux method for
estimating the gas transfer velocity. However, according to the laboratory
test of Richardson et al. (2000), this method exhibited significant differences
between the heat and gas exchange data for large upward net-flux
conditions. The version of this method recently developed by the same team
of investigators but employing the properties of the “natural” cool skin on
the ocean surface, which is basically the Soloviev and
(1994)
approach, performs very well (Garbe et al., 2002).
483
Schl ssel
ü
Schl ssel
ü
molecular sublayers at the free ocean surface and at a rigid wall may not be
complete. Here, we explore only the application of the surface renewal
approach for modeling the interfacial component of gas exchange.
The renewal of the ocean surface water can occur because of convective,
shear or surface wave instabilities. Portions of fluid are ejected from the
molecular boundary layers into deeper layers, thus providing the renewal of
the surface water. The renewal rate therefore determines the interfacial
fluxes. Csanady (1990) linked the surface renewal with the presence of flow
convergences. The surface convergence zones are usually relatively narrow
and quasi-periodic in space and/or time. The so-called “rollers” (or microscale wave breakings) provide maximum flow convergence.
Modeling surface renewal is based on the relationships connecting the
renewal rate to the environmental parameters such as friction velocity, heat
fluxes etc. Surface films can influence the surface renewal process,
especially under low wind speed conditions (Frew, 1997).
The thermal molecular sublayer of the ocean (cool skin) does not
substantially influence the heat exchange between ocean and atmosphere
except in some extreme conditions (Paulson and Simpson, 1981). At the
same time, air-sea gas transport does substantially depend on parameters of
the oceanic diffusion sublayer. Due to low gas diffusivity in water compared
to the rather high gas diffusivity in air, the diffusion sublayer provides the
main resistance to the interfacial atmosphere-ocean gas transport (Bolin,
1960).
Despite different roles in the heat and gas exchange at the air-sea
interface, the thermal and diffusion sublayers are governed by similar laws.
Soloviev and
(1994) proposed relating the temperature difference
across the thermal sublayer (cool skin of the ocean), 'T, to the interfacial
(direct) gas transfer velocity (K t ) (Section 2.3). The more readily available
cool skin data are then used for an adjustment of the gas transfer
parameterization. A further extension of the renewal model includes the
effects of solar radiation and rainfall on the molecular boundary layers
(Sections 2.4 and 2.5).
Jaehne et al. (1987) proposed the controlled heat flux method for
estimating the gas transfer velocity. However, according to the laboratory
test of Richardson et al. (2000), this method exhibited significant differences
between the heat and gas exchange data for large upward net-flux
conditions. The version of this method recently developed by the same team
of investigators but employing the properties of the “natural” cool skin on
the ocean surface, which is basically the Soloviev and
(1994)
approach, performs very well (Garbe et al., 2002).
483
Schl ssel
ü
Schl ssel
ü