Geoscience Reference
In-Depth Information
In such actively unstable conditions,
with very strong currents and
strong winds, the air-sea fluxes are not well known: getting near
surface measurements is difficult, and the surface itself is not well-
defined, because of the widespread presence of sea spray in the air
and the penetration of air bubbles in the water. It is, therefore, mainly
a
posteriori,
by comparing different numerical simulations of the sea
surface temperature evolution, and through the means of heat
balances, that it has been possible to precisely estimate fluxes and air-
sea exchanges.
Moreover, the impact that an oceanic haline stratification can have
on cyclones should be noted. This stratification is present at least
seasonally in numerous regions where cyclones intensify. This is the
case, for example, in the region East of the Antilles Islands, in
summer and autumn, due to inputs of fresh water from the large
South-American rivers; it is the case, too, in the Bay of Bengal,
especially after the monsoon, when very large supplies of fresh water
from the rivers penetrate far from the coasts into the open ocean. In
these regions, haline stratification is often distinct from the thermal
stratification. Here, the pull into deeper layers and the turbulent
mixing at the base of the surface layer (whose thickness is restricted
by the salinity) do not cause any surface cooling. In this case, the
friction of the wind destroys the haline stratification but not the
thermal stratification. This was observed using the SMOS mission, on
several cyclones crossing the fresh water area in East of the Antilles
Islands in 2010 and 2011 (at around 50 and 60 W) [GRO 12].
Cyclones are also associated with heavy precipitation. The
Tropical Rainfall Microwave Mission (TRMM) space mission has
permitted an exceptional documentation of the structure of many
cyclones due to its precipitation radar (PR). The above-mentioned
regions with strong evaporation are not in general in the same areas as
the regions with heavy precipitation. Cyclones can thus be considered
as redistributors of fresh water, and contribute locally to a haline
stratification of the surface layers.
