Impact of geoid definition on the simulated strength of the equatorial undercurrent in a global data assimilation system.
Dr Femke Vossepoel(1), Dr Johannes Bouman(2)
, Dr Radboud Koop(2)
, Marc Naeije(3)
, and Dr Peter Jan Van Leeuwen(4)
3584 CC Utrecht,
(2) SRON, Sorbonnelaan 2, 3584 CA Utrecht, Netherlands
(3) DEOS, Kluyverweg 1, 2629 HS Delft, Netherlands
(4) IMAU, Princetonplein 5, 3584 CC Utrecht, Netherlands
The availability of gravity data from recent satellite missions (CHAMP, GRACE)
and the future GOCE mission will improve our current knowledge of the Earth's
geoid. An accurate description of the geoid is essential for a proper
interpretation of altimetric sea level data, which can help us to better understand
the ocean circulation. This study evaluates the sensitivity of an estimated ocean
circulation to the definition of the geoid, using a global ocean circulation model
(OGCM) and an advanced data assimilation technique.
In the analysis system, Topex/Poseidon altimetric sea level heights are related
to modeled sea level. Instead of using sea level anomalies with respect to a
long-term mean, which is the most common usage of altimetry, the absolute sea
level minus the geoid estimate is assimilated. In the current study, we adopt
TOPEX/Poseidon altimetry and incorporate the most recent geoid solutions
based on satellite data (GRIM5-S1, EIGEN-2, GRACE).
The analysis system consists of the OPA OGCM, in which observations are
being assimilated. The assimilation technique, the sequential importance
resampling (SIR), is an ensemble-based method, that determines the optimal
model trajectory by statistical evaluation of a number of perturbed model
simulations. The implementation of this technique is especially efficient in a
parallel computing environment.
Specific attention is being paid to the equatorial undercurrent in the Atlantic,
Indian and Pacific Oceans. We evaluate the impact of the geoid definition on its
strength and its variability, and discuss the implications of improving geoid
accuracies for the estimation of ocean circulation.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,