THE NEAR-SURFACE LAYER OF THE OCEAN
a simple power law fit to an aerosol mode located at ~1 µm D p , which might
be too simple to reproduce the observed properties.
The underestimation in the 0.07–0.9 µm D p range and the overestimation
in the D p < 0.07 µm range partly cancel each other when the total number
flux is determined. However, the differences below 0.9 µm D p may have
serious implications concerning the contribution of the primary marine
aerosol source to the cloud condensation nuclei (CCN) population.
Consequently, these two parameterizations are likely to result in different
cloud properties and radiative forcing. The parameterization of Mårtensson
et al. (2003) in the D p < 0.9 µm range is probably more realistic, because this
range is outside the range of the experimental data on which Monahan et al.
(1986) based their parameterization.
For D p = 0.9–3.0 µm, both Mårtensson et al. (2003) and Monahan et al.,
(1986) predict almost the same aerosol generation rates.
Spray droplets that eventually become the main component of the marine
aerosol are typically smaller than those that most influence air-sea heat and
moisture transfer. The latter are in the range r 0 = 2–500 Pm (remember that
r 0 is the radius of droplets, while D p is the diameter of dry aerosol particles).
6.3 Air-Sea Exchange During High Wind Speeds
6.3.1 Effect of spray on air-sea exchanges
Spume droplets, which are relatively large, are particularly important for
the fluxes carried by sea spray. Andreas (1998) and Andreas and Emanuel
(2001) made an estimate of the effect of the sea spray on heat, moisture, and
momentum transfer involving the sea spray generation function that was
extended into the range of spume droplet sizes. These authors employed a
sea spray generation function valid in the droplet radius range from 2 Pm to
500 Pm based on the Andreas (1992) and modified Smith et al. (1993)
parameterizations.
Figure 6-13 shows estimates of the magnitude of the sensible and latent
heat fluxes based on the Andreas (1992) spray model and two formulations
for the spray generation function—the one developed in Andreas (1992) and
the modified parameterization of Smith et al. (1993). Differences between
these generation functions are observed only for U 10 < 15–16 m s
-1 , when the
contributions of sea spray to air-sea fluxes of heat and moisture are small.
Figure 6-13 suggests the possibility of extremely large contributions of sea
spray to heat and moisture transfer during storms.
Sea spray represents a volume source of heat and humidity in the marine
boundary layer. The temperature and humidity profiles can be so strongly
modified near the surface by the effects of evaporating spray that additional
feedbacks may occur (Katsaros and de Leeuw, 1994). The contribution of
424
a simple power law fit to an aerosol mode located at ~1 µm D p , which might
be too simple to reproduce the observed properties.
The underestimation in the 0.07–0.9 µm D p range and the overestimation
in the D p < 0.07 µm range partly cancel each other when the total number
flux is determined. However, the differences below 0.9 µm D p may have
serious implications concerning the contribution of the primary marine
aerosol source to the cloud condensation nuclei (CCN) population.
Consequently, these two parameterizations are likely to result in different
cloud properties and radiative forcing. The parameterization of Mårtensson
et al. (2003) in the D p < 0.9 µm range is probably more realistic, because this
range is outside the range of the experimental data on which Monahan et al.
(1986) based their parameterization.
For D p = 0.9–3.0 µm, both Mårtensson et al. (2003) and Monahan et al.,
(1986) predict almost the same aerosol generation rates.
Spray droplets that eventually become the main component of the marine
aerosol are typically smaller than those that most influence air-sea heat and
moisture transfer. The latter are in the range r 0 = 2–500 Pm (remember that
r 0 is the radius of droplets, while D p is the diameter of dry aerosol particles).
6.3 Air-Sea Exchange During High Wind Speeds
6.3.1 Effect of spray on air-sea exchanges
Spume droplets, which are relatively large, are particularly important for
the fluxes carried by sea spray. Andreas (1998) and Andreas and Emanuel
(2001) made an estimate of the effect of the sea spray on heat, moisture, and
momentum transfer involving the sea spray generation function that was
extended into the range of spume droplet sizes. These authors employed a
sea spray generation function valid in the droplet radius range from 2 Pm to
500 Pm based on the Andreas (1992) and modified Smith et al. (1993)
parameterizations.
Figure 6-13 shows estimates of the magnitude of the sensible and latent
heat fluxes based on the Andreas (1992) spray model and two formulations
for the spray generation function—the one developed in Andreas (1992) and
the modified parameterization of Smith et al. (1993). Differences between
these generation functions are observed only for U 10 < 15–16 m s
-1 , when the
contributions of sea spray to air-sea fluxes of heat and moisture are small.
Figure 6-13 suggests the possibility of extremely large contributions of sea
spray to heat and moisture transfer during storms.
Sea spray represents a volume source of heat and humidity in the marine
boundary layer. The temperature and humidity profiles can be so strongly
modified near the surface by the effects of evaporating spray that additional
feedbacks may occur (Katsaros and de Leeuw, 1994). The contribution of
424