Geoscience Reference
In-Depth Information
NASA MODIS and SeaWiFS data. These products have been averaged at the SMOS L3
product 0.25 resolution, with a 10-day running mean.
2.5 In Situ Data
Salinity measurements from Argo floats are provided by the Coriolis data center (
http://
www.coriolis.eu.org/
)
. The upper ocean salinity values recorded between 4- and 10-m
depth will be referred to as Argo SSS following Boutin et al. (
2012b
).
Global SSS maps are derived from delayed time quality checked in situ measurements
(Argo and ship) by IFREMER/LPO, Laboratoire de Physique des Oceans, using the In Situ
Analysis System (ISAS) optimal interpolation (D7CA2S0 re-analysis product) (see a
method description on
http://wwz.ifremer.fr/lpo/SO-Argo-France/Products/Global-Ocean-
T-S/Monthly-fields-2004-2010
and in (Gaillard et al.
2009
)). The choice for the time and
space scales used in that method results from a compromise between what is known
of ocean time and space scales and what can actually be resolved with the Argo array
(3, 10 days); two length scales are considered: the first one is isotropic and equal to
300 km, the second one is set equal to 4 times the average Rossby radius of deformation of
the area. As a result, we expect these maps being smoother, especially in tropical areas,
than SMOS SSS maps averaged over 0.25 9 0.25 or 1 9 1.
3 SMOS Monitoring of the Major Tropical Atlantic River Plumes
Rivers are important variables in oceanography as their freshwater affects SSS and the
buoyancy of the surface layer, and they represent a source of materials exotic to the ocean
and important to biological activity. Obviously, they are key hydrologic components of the
freshwater exchanges between land and ocean. Despite this importance, tracing major
tropical river water (e.g., Amazon, Congo, and Ganges) over large distances has not been
straightforward previously principally because of a lack of SSS observations. Tracing those
very large rivers over great distances now become an important endeavor, as sufficient data
are available from surface salinity sensors placed aboard satellites.
Occurrence of patches of low surface salinity (\35 practical salinity scales) in the
tropical Atlantic Ocean is closely related to the presence of the mouths of the world's
largest rivers in terms of freshwater discharge (e.g., Amazon, Congo, and Orinoco) and
their subsequent spreading of freshwater by the upper ocean circulation. Another key
freshwater source here is the Inter Tropical Convergence Zone (ITCZ), associated with
relatively intense precipitation that migrates latitudinally over the tropical Atlantic
throughout the year (Binet and Marchal
1993
). One of these major low-salinity pools is
formed by the Amazon and Orinoco river plumes spreading offshore from the South
America northeastern coasts, and influencing a large fraction of the western tropical North
Atlantic (Neumann
1969
; Lentz
1995
; Muller-Karger et al.
1988
; Dessier and Donguy
1994
). The Gulf of Guinea situated in the northeastern equatorial Atlantic is also an
important location for the freshwater budget in the tropical Atlantic. It is a region of intense
precipitation with as much as 30 cm of rain falling per month during the rainy season (Yoo
and Carton
1988
). Furthermore, into this area flows the Congo River, the largest freshwater
input to any eastern ocean boundary. These large-scale low-salinity ''lenses'' at the tropical
Atlantic surface can be traced over distances ranging from several hundred up to thousands
of kilometers in the upper ocean. They are characterized by very distinct and in general
strong seasonally varying spatial extents.
