SURFACE FLUXES
237
coast of Antarctica where offshore winds can keep significant portions of
the ocean surface ice-free.
2.3
Air-ice fluxes
Including a SIM within the GODAE system eliminates the need to
specify ice-ocean fluxes, though observed sea-ice fraction should probably be assimilated, but requires data sets for computing all the air-ice
fluxes. In general a sea-ice model has a number of ice categories. The
air-ice heat and water fluxes for a particular ice category, n, are given
by
Q
n
ai = Q
n
S + Q
n
L + Q
n
E + Q
n
H
F
n
ai = P
n + E
n
(12)
Ice models differentiate between snow and rain. The former becomes P n
in (12), which accumulates in the snow layer atop ice category, n, with
surface temperature, T n
S , while the rain is often passed directly to the
ocean below, as a contribution to F io in (4).
Given a shortwave insolation data set, ice models typically split this
radiation into four components; visible (wavelengths from 0.3 to 0.7µ)
direct, visible diffuse, near-infrared (0.7 to 3µ) direct and near-infrared
diffuse. An ice model then must provide the respective albedos; α n
V dr ,
α n
V df , α n
Ndr and α n
Ndf , for each ice category, n. In order to use Q I data
the respective fractions are needed, with .29, .24, .31, .16 an acceptable
partitioning:
Q
n
S = Q I [.29(1 − α
n
V dr ) + .31(1 − α
n
V df ) + .24(1 − α
n
Ndr ) + .16(1 − α
n
Ndf )].
(13)
It is simpler to utilize downwelling long-wave radiation, because there is
no need to do any partitioning. The net long-wave radiation becomes:
Q
n
L = i Q A − i σ(T
n
S )
4 ,
(14)
where i = 0.95, is the ice/snow emissivity. This emissivity is also used
in the first term on the right-hand-side of (14) as 1 minus a longwave
albedo.
2.4
Continental runoff
Very complex estuarine process govern runoff into the ocean, and may
be beyond the scope of GODAE. However, it is important to capture the
concentration near coastlines, especially at the mouths of large rivers.
There should also be a representation of seasonality, including the storage of snowfall. For example, extratropical runoff can be made to peak
237
coast of Antarctica where offshore winds can keep significant portions of
the ocean surface ice-free.
2.3
Air-ice fluxes
Including a SIM within the GODAE system eliminates the need to
specify ice-ocean fluxes, though observed sea-ice fraction should probably be assimilated, but requires data sets for computing all the air-ice
fluxes. In general a sea-ice model has a number of ice categories. The
air-ice heat and water fluxes for a particular ice category, n, are given
by
Q
n
ai = Q
n
S + Q
n
L + Q
n
E + Q
n
H
F
n
ai = P
n + E
n
(12)
Ice models differentiate between snow and rain. The former becomes P n
in (12), which accumulates in the snow layer atop ice category, n, with
surface temperature, T n
S , while the rain is often passed directly to the
ocean below, as a contribution to F io in (4).
Given a shortwave insolation data set, ice models typically split this
radiation into four components; visible (wavelengths from 0.3 to 0.7µ)
direct, visible diffuse, near-infrared (0.7 to 3µ) direct and near-infrared
diffuse. An ice model then must provide the respective albedos; α n
V dr ,
α n
V df , α n
Ndr and α n
Ndf , for each ice category, n. In order to use Q I data
the respective fractions are needed, with .29, .24, .31, .16 an acceptable
partitioning:
Q
n
S = Q I [.29(1 − α
n
V dr ) + .31(1 − α
n
V df ) + .24(1 − α
n
Ndr ) + .16(1 − α
n
Ndf )].
(13)
It is simpler to utilize downwelling long-wave radiation, because there is
no need to do any partitioning. The net long-wave radiation becomes:
Q
n
L = i Q A − i σ(T
n
S )
4 ,
(14)
where i = 0.95, is the ice/snow emissivity. This emissivity is also used
in the first term on the right-hand-side of (14) as 1 minus a longwave
albedo.
2.4
Continental runoff
Very complex estuarine process govern runoff into the ocean, and may
be beyond the scope of GODAE. However, it is important to capture the
concentration near coastlines, especially at the mouths of large rivers.
There should also be a representation of seasonality, including the storage of snowfall. For example, extratropical runoff can be made to peak