THE NEAR-SURFACE LAYER OF THE OCEAN
important role of waves in determining the momentum fluxes across the airsea interface motivated the inclusion of spectral wave submodels in
operational numerical weather prediction models at NOAA/NCEP and
ECMWF. For some applications, the wave fields are of direct utility.
Another example is the use of a biological submodel to predict turbidity for
an ocean GCM. However, the biogeochemical processes and their interaction
with physics near the air-sea interface represent a fundamental challenge for
modeling climate variability and change because the appropriate equations
are not yet fully developed.
Below, we discuss the representation of near-surface processes in the
context of surface boundary conditions and near-surface subgrid scale
parameterizations for numerical ocean models, and the possible roles of
these processes in ocean and climate simulation and prediction.
7.6.1 Air-Sea Fluxes
Air-sea fluxes depend not only on the conditions in the atmosphere, but
also on processes in the upper ocean boundary layer. Surface gravity waves
are only the most obvious example. Thus, there is a coupled nature to ocean
surface boundary conditions, and ocean models that are driven by specified
fluxes cannot take these feedbacks into account. Coupled ocean-atmosphere
models can, in principal, take them into account, but they generally do not
have the vertical resolution to do so. Thus, these effects must be
parameterized.
a) Wave-mediated momentum fluxes
At the present time, neither ocean general circulation models nor
coupled climate models include the effects of surface waves, except as
crudely parameterized by a wind-speed dependent drag coefficient. The flux
of momentum from the atmosphere to the ocean (or vice-versa under calm
winds) intimately involves the surface wave field, which depends on the
history of the wind locally and at remote locations. The surface wind stress
depends on the wave roughness, and the accurate partitioning of atmospheric
momentum into the wave field and into the surface currents is a challenging
problem. Properly accounting for these influences includes consideration of
the Stokes drift due to wave radiation stress, spray effects (see below), and
of the turbulence created when waves break.
498
important role of waves in determining the momentum fluxes across the airsea interface motivated the inclusion of spectral wave submodels in
operational numerical weather prediction models at NOAA/NCEP and
ECMWF. For some applications, the wave fields are of direct utility.
Another example is the use of a biological submodel to predict turbidity for
an ocean GCM. However, the biogeochemical processes and their interaction
with physics near the air-sea interface represent a fundamental challenge for
modeling climate variability and change because the appropriate equations
are not yet fully developed.
Below, we discuss the representation of near-surface processes in the
context of surface boundary conditions and near-surface subgrid scale
parameterizations for numerical ocean models, and the possible roles of
these processes in ocean and climate simulation and prediction.
7.6.1 Air-Sea Fluxes
Air-sea fluxes depend not only on the conditions in the atmosphere, but
also on processes in the upper ocean boundary layer. Surface gravity waves
are only the most obvious example. Thus, there is a coupled nature to ocean
surface boundary conditions, and ocean models that are driven by specified
fluxes cannot take these feedbacks into account. Coupled ocean-atmosphere
models can, in principal, take them into account, but they generally do not
have the vertical resolution to do so. Thus, these effects must be
parameterized.
a) Wave-mediated momentum fluxes
At the present time, neither ocean general circulation models nor
coupled climate models include the effects of surface waves, except as
crudely parameterized by a wind-speed dependent drag coefficient. The flux
of momentum from the atmosphere to the ocean (or vice-versa under calm
winds) intimately involves the surface wave field, which depends on the
history of the wind locally and at remote locations. The surface wind stress
depends on the wave roughness, and the accurate partitioning of atmospheric
momentum into the wave field and into the surface currents is a challenging
problem. Properly accounting for these influences includes consideration of
the Stokes drift due to wave radiation stress, spray effects (see below), and
of the turbulence created when waves break.
498