Geoscience Reference
In-Depth Information
3.2.4.4.
Export of particles
Finally, the ocean's surface layers are also the source of primary
aerosols during the evaporation of sea spray, or from the bursting of
bubbles at the surface. They mediate the export of different salts,
which often contribute to the condensation nuclei of clouds, thus
modifying their radiative properties and concentration in the regions
concerned. These primary aerosols can also lead to secondary reactions
in clouds and have impacts on the atmosphere's oxidizing properties.
Finally, they contain the organic compounds of the surface films,
whose chemistry and interactions with atmospheric properties are still
a vast area of study.
3.2.5.
Flux measurement
To quantify surface fluxes, it is necessary to estimate their
magnitude, directly (by measurements) or indirectly. The principal
approaches used and contested issues are presented in this section.
3.2.5.1.
Radiative fluxes
The measurement of radiative fluxes is made locally with specific
instruments: the radiometer (for solar radiation), pyranometer (IR
radiation) and pyrgeometer. These sensors are made up of materials
that transform the input into an electric current inside a transparent
cell. For example, in the pyrgeometer, the sensitive element that is
exposed to infrared radiation is a thermopile, the solar radiation being
eliminated by a non-reflective black paint. The thermopile delivers an
electric potential difference proportionate to the difference between
the received radiative flux and that emitted by the sensitive surface of
the thermopile.
Radiation profiles in the ocean are measured by different sensors
that can be operated from ships, or in automatic versions, installed on
moored buoys or profiling floats: sensors for solar radiation or
multifrequency radiative measurements, chlorophyll-A fluorescence
or dissolved colored matter, as well as absorption profiles (by
transmissiometry).
