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Ocean State Estimation |
| Physical Oceanography |
Ocean data assimilation is directed at the combined use of ocean data and models to determine the general circulation of the ocean, on a global continuous basis. The central element for this activity is a numerical circulation model that is constrained by (combined with) ocean data. Accordingly ocean state estimation deals with a rich variety of problems including computers and networks, numerical formulation of partial differential equations, statistical analyses and descriptions of the ocean, and the interpretation of ocean data.
The goal of ocean state estimation (data assimilation) is to obtain the best possible estimate of the changing ocean. This has much in common with modern numerical weather forecasting. But because observations are much sparser in the ocean and the memory of the ocean is much longer than that of the atmosphere, challenges for ocean estimation and prediction are substantially greater that those in the atmosphere.
Results are being used to study the ocean, its dynamics and kinematics,
transport properties, and interaction with the atmosphere.
Everything that is difficult to observe directly will
be addressed by the outcome of models. Our present focus
is on the time evolving global
circulation as it emerges from global hydrography and current
data and from the TOPEX/POSEIDON
altimeter observations globally and in regional higher resolution models.
Results will be used to
understand, in particular, the oceanic heat and fresh water fluxes,
their divergences, their dynamical
causes and effects, as well as a variety of related issues connecting
the oceanic circulation to
climate variability. An example of the resulting circulation is shown
in the figure. All major
currents are estimated, but due to the low spatial resolution,
results are very smooth as compared to
the real world.
Figure: The ocean circulation and overlaying atmospheric surface
forcing fields: The upper part
shows monthly mean fields of the net sea surface heat flux (positive
into the ocean) and the surface
wind stress (white vector field, in N/m2) as provided by the National
Center for Environmental Prediction
(NCEP) re-analysis for January 1993. The contour increment for the
heat flux is 30 W/m2 and the range
covers -670 W/m2 over the Kuroshio and about 215 W/m2 in the southern
hemisphere.
The lower panel shows the circulation of the Pacific Ocean at 63
m depth (blue vector field) as it results
for 1993 by combining an ocean circulation model with one year of
absolute TOPEX/POSEIDON sea surface
height data relative to a geoid model, (2) the time dependent T/P
sea surface height component, (3) the
time-varying NCEP wind stress and surface fluxes of heat and fresh
water over the full year, and
(4) the annual mean theta, S climatology. Also shown is the sea
surface height field which is associated
with the interior ocean flow field. The contour increment is 20
cm and the range extends from -180 cm in
the southern part to 95 cm off Japan. See text for details.
Ocean state estimation is gaining increasing national and international attention and will be an essential element in future large-scale and climate experiments. Its role in SIO teaching and education is therefore increasing, and this field offers exciting research topics for students with interests in technical issues, theory, or data analysis. Applications range from the global scale down to regional high-resolution approaches. And in the near future coastal applications will gain importance as well.
Scripps faculty involved in ocean state estimation include:
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Physical Oceanography at Scripps