Sea salt particles are an important part of the atmospheric sulfur cycle
(Chamides and Stelson, 1992). According to O'Dowd et al. (1999), natural
and anthropogenic sulfate aerosols influence the climate. The
Intergovernmental Panel on Climate Change (2001) estimated the direct and
indirect radiative forcing of sulfate aerosols to be in the range -0.2 to -0.8 W
m
-2 and 0 to -1.5 W m
-2 , respectively. This is comparable in magnitude to the
radiative forcing of anthropogenic greenhouse gases. It is important that
sulfate aerosols produce a radiative effect that is opposite in sign to that of
anthropogenic greenhouse gases.
In addition to affecting climate, marine spray and aerosols transfer
pollutants from the ocean to the atmosphere, serve as a tracer in the climate
record of Arctic and Antarctic snow and ice cores, play a role for corrosion,
and cause vegetation stress in coastal regions. The optical properties of the
marine boundary layer depend substantially on the type and concentration of
aerosols.
Note here that some studies cited below, like that of Andreas (1998), use
the diameter of wet particles (i.e., of droplets), while others like that of
Mårtensson et al. (2003) use the diameters of dry particles. This can be
attributed to different applications of marine aerosol results. Air-sea
interaction scientists are interested in the influence of marine aerosols on the
air-sea fluxes, while climatologists are mostly concerned with the presence
of dry aerosol particles in the atmosphere. Respectively, different definitions
for the sea spray and aerosol generation functions can be found in the
literature. In particular, Mårtensson et al. (2003) uses the marine aerosol
generation function defined via the dry diameter of aerosol particle; while,
Monahans’s sea spray generation function operates with the radius of a
droplet at its formation r 0 .
6.2.2 Mechanisms of sea spray production
There are basically three varieties of spray droplets: film droplets, jet
droplets, and spume droplets. First consider film and jet droplets.
Bursting air-bubbles create film and jet droplets. Bubbles are primarily
generated through entrainment by breaking waves (Thorpe, 1986). After
being carried to some depth by a plunging wave jet, a bubble then rises to
the surface where it bursts. The process of bursting is schematically
illustrated in Figure 6-7. As the bubble emerges from the water, a thin film
forms at the upper surface of the bubble; the film thins by drainage and
eventually ruptures. When the bubble film opens, the rim of the receding
film cap ejects tens to hundreds of film droplets with radii ranging roughly
from 0.5 to 5 Pm (Spiel, 1998). The collapsing bubble cavity shoots up a jet
of water from its bottom. Due to velocity differences along this jet, it soon
Chapter 6: HIGH WIND SPEED REGIME
411
(Chamides and Stelson, 1992). According to O'Dowd et al. (1999), natural
and anthropogenic sulfate aerosols influence the climate. The
Intergovernmental Panel on Climate Change (2001) estimated the direct and
indirect radiative forcing of sulfate aerosols to be in the range -0.2 to -0.8 W
m
-2 and 0 to -1.5 W m
-2 , respectively. This is comparable in magnitude to the
radiative forcing of anthropogenic greenhouse gases. It is important that
sulfate aerosols produce a radiative effect that is opposite in sign to that of
anthropogenic greenhouse gases.
In addition to affecting climate, marine spray and aerosols transfer
pollutants from the ocean to the atmosphere, serve as a tracer in the climate
record of Arctic and Antarctic snow and ice cores, play a role for corrosion,
and cause vegetation stress in coastal regions. The optical properties of the
marine boundary layer depend substantially on the type and concentration of
aerosols.
Note here that some studies cited below, like that of Andreas (1998), use
the diameter of wet particles (i.e., of droplets), while others like that of
Mårtensson et al. (2003) use the diameters of dry particles. This can be
attributed to different applications of marine aerosol results. Air-sea
interaction scientists are interested in the influence of marine aerosols on the
air-sea fluxes, while climatologists are mostly concerned with the presence
of dry aerosol particles in the atmosphere. Respectively, different definitions
for the sea spray and aerosol generation functions can be found in the
literature. In particular, Mårtensson et al. (2003) uses the marine aerosol
generation function defined via the dry diameter of aerosol particle; while,
Monahans’s sea spray generation function operates with the radius of a
droplet at its formation r 0 .
6.2.2 Mechanisms of sea spray production
There are basically three varieties of spray droplets: film droplets, jet
droplets, and spume droplets. First consider film and jet droplets.
Bursting air-bubbles create film and jet droplets. Bubbles are primarily
generated through entrainment by breaking waves (Thorpe, 1986). After
being carried to some depth by a plunging wave jet, a bubble then rises to
the surface where it bursts. The process of bursting is schematically
illustrated in Figure 6-7. As the bubble emerges from the water, a thin film
forms at the upper surface of the bubble; the film thins by drainage and
eventually ruptures. When the bubble film opens, the rim of the receding
film cap ejects tens to hundreds of film droplets with radii ranging roughly
from 0.5 to 5 Pm (Spiel, 1998). The collapsing bubble cavity shoots up a jet
of water from its bottom. Due to velocity differences along this jet, it soon
Chapter 6: HIGH WIND SPEED REGIME
411