Geoscience Reference
In-Depth Information
This absorption (and therefore emission, according to the law “any
body in thermodynamic equilibrium that absorbs radiation re-emits the
same quantity”) by the atmospheric components is responsible for the
greenhouse effect: the presence of some cloud types, and above all of
water vapor and
CO
2
, prevents the cooling of the lower atmosphere
and surface. For example, on a clear, dry night, the atmosphere
contributes very little to warming the Earth's surface, which thus
cools by emitting infrared radiation.
3.2.1.3.
The radiation penetrating the ocean
The radiation penetrating the ocean is partly used up through
phytoplanktonic activity and
through absorption in phytoplanktonic
cells, enabling photosynthesis produced by certain pigments, but in
particular chlorophyll pigments. In compensation, these cells, along
with particular organic matter called colored matter (often in a
dissolved state), re-emit the radiation in less energetic wavelengths (by
fluorescence). However, the proportion stored in the form of chemical
energy is weak, and the energy absorbed is rapidly transformed into
heat, leading to a warming of the layers. These cells, just like other
marine particles of biological or mineral origin and numerous
dissolved substances, also refract part of the light received. From these
interactions results a greater vertical “thermal”
stratification of the
surface layers. Moreover, light penetrates less deeply when these
particles are present, which inhibits photosynthetic production in the
deepest layers. Because of the surface warming, the long wave fluxes
emitted at the surface of the ocean are significantly increased.
Furthermore, the presence of organic and inorganic particles and
dissolved colored matter in the surface layers slightly modifies the
short wave radiation re-emitted by the surface (an albedo effect); these
two effects have an impact on the planet's radiative balance.
3.2.2.
Turbulent fluxes
While the surface radiative fluxes depend on numerous “players”
outside the interface (notably, sunshine and clouds), the turbulent
