Chapter 1: INTRODUCTION
where 'C is the effective air-sea gas concentration difference, and K P is the
gas transfer (piston) velocity. Expressed in terms of the gas partial pressure
in water (p w ) and in air (p a ), and gas solubility S P , formula (1.44) reads as
follows:
0
(
)
w
a
G K S p
p
P P
.
(1.45).
Strictly speaking, partial pressure in equation (1.45) should be replaced
with gas fugacity (DOE, 1994). The fugacity of an ideal gas is simply its
partial pressure. In terms of fugacity, the thermodynamic relationships for
real (non-ideal) gases coincide with those established for ideal gases. An
example of non-ideal gas is CO 2 . For typical oceanic conditions, the
difference between the CO 2 partial pressure and CO 2 fugacity is, however,
only about 1 µatm, which is about 0.3% of the CO 2 fugacity in seawater.
The air-sea gas transfer velocity K P is determined by the properties of
the turbulent boundary layer and sea surface (Section 7.5.1), while simplified
parameterization formulas imply that K P is a function of wind speed only. A
complicating issue is the bubble-mediated gas transport because it is a
volume source, which depends on bubble dynamics (see Chapter 7).
Representation of the volume source term G V in equation (1.12) involves
such issues as gas solubility, bubble-mediated transport, and, in many cases,
bio- and photochemical reactions in the sea surface microlayer.
1.3.3 Long-wave radiation
In many instances, the longwave radiation emitted from the sea surface
(longwave exitance) is nearly balanced by the downward longwave radiation
(longwave irradiance) emitted primarily from moisture in the atmosphere. It
is possible, however, for the difference to be significant. To compute
longwave exitance it is assumed that the ocean radiates as a gray body. This
implies that the longwave exitance is proportional to the fourth power of the
absolute sea surface temperature when expressed in degrees Kelvin (K).
The net long wave radiation flux is parameterized as follows:
4
0
L
w
w a
I
T
E
H V
H
,
(1.46)
where
4
2
8
10
67
.
5
u
K
m
W
V
is the Stefan-Boltzmann constant, 0
T is
the sea surface temperature,
0.97
w
H |
is the infrared emissivity of water
(fraction of black-body radiation), and E a is the long wave irradiance from
the sky that can be measured with an Eppley Precision Infrared Radiometer
or calculated with an existing algorithm (see Katsaros (1990) for a review).
19
where 'C is the effective air-sea gas concentration difference, and K P is the
gas transfer (piston) velocity. Expressed in terms of the gas partial pressure
in water (p w ) and in air (p a ), and gas solubility S P , formula (1.44) reads as
follows:
0
(
)
w
a
G K S p
p
P P
.
(1.45).
Strictly speaking, partial pressure in equation (1.45) should be replaced
with gas fugacity (DOE, 1994). The fugacity of an ideal gas is simply its
partial pressure. In terms of fugacity, the thermodynamic relationships for
real (non-ideal) gases coincide with those established for ideal gases. An
example of non-ideal gas is CO 2 . For typical oceanic conditions, the
difference between the CO 2 partial pressure and CO 2 fugacity is, however,
only about 1 µatm, which is about 0.3% of the CO 2 fugacity in seawater.
The air-sea gas transfer velocity K P is determined by the properties of
the turbulent boundary layer and sea surface (Section 7.5.1), while simplified
parameterization formulas imply that K P is a function of wind speed only. A
complicating issue is the bubble-mediated gas transport because it is a
volume source, which depends on bubble dynamics (see Chapter 7).
Representation of the volume source term G V in equation (1.12) involves
such issues as gas solubility, bubble-mediated transport, and, in many cases,
bio- and photochemical reactions in the sea surface microlayer.
1.3.3 Long-wave radiation
In many instances, the longwave radiation emitted from the sea surface
(longwave exitance) is nearly balanced by the downward longwave radiation
(longwave irradiance) emitted primarily from moisture in the atmosphere. It
is possible, however, for the difference to be significant. To compute
longwave exitance it is assumed that the ocean radiates as a gray body. This
implies that the longwave exitance is proportional to the fourth power of the
absolute sea surface temperature when expressed in degrees Kelvin (K).
The net long wave radiation flux is parameterized as follows:
4
0
L
w
w a
I
T
E
H V
H
,
(1.46)
where
4
2
8
10
67
.
5
u
K
m
W
V
is the Stefan-Boltzmann constant, 0
T is
the sea surface temperature,
0.97
w
H |
is the infrared emissivity of water
(fraction of black-body radiation), and E a is the long wave irradiance from
the sky that can be measured with an Eppley Precision Infrared Radiometer
or calculated with an existing algorithm (see Katsaros (1990) for a review).
19