Relative performance of future altimeter systems and tide gauges in constraining a model of North Sea high-frequency barotropic dynamics |
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| Authors: | Baptiste Mourre Pierre De Mey Yves Ménard Florent Lyard Christian Le Provost |
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| Institution: | (1) LEGOS, 14, Av. Edouard Belin, 31400 Toulouse, France;(2) Institut de Ciències del Mar, Physical Oceanography Group, Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain |
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| Abstract: | We evaluate in this paper the ability of several altimeter systems, considered separately as well as together with tide gauges,
to control the time evolution of a barotropic model of the North Sea shelf. This evaluation is performed in the framework
of the particular model errors due to uncertainties in bathymetry. An Ensemble Kalman Filter (EnKF) data assimilation approach
is adopted, and observing-systems simulation experiments (OSSEs) are carried out using ensemble spread statistics. The skill
criterion for the comparison of observing networks is, therefore, not based on the misfit between two simulations, as done
in classic twin experiments, but on the reduction of ensemble variance occurring as a consequence of the assimilation. Future
altimeter systems, such as the Wide Swath Ocean Altimeter (WSOA) and satellite constellations, are considered in this work.
A single WSOA exhibits, for instance, similar performance as two-nadir satellites in terms of sea-level correction, and is
better than three satellites in terms of model velocity control. Generally speaking, the temporal resolution of observations
is shown to be of major importance for controlling the model error in these experiments. This result is clearly related to
the focus adopted in this study on the specific high-frequency response of the ocean to meteorological forcing. Altimeter
systems lack adequate temporal sampling for properly correcting the major part of model error in this context, whereas tide
gauges, which provide a much finer time resolution, lead to better global statistical performance. When looking into further
detail, tide gauges and altimetry are demonstrated to exhibit an interesting complementary character over the whole shelf,
as tide gauge networks make it possible to properly control model error in a ∼100-km coastal band, while high-resolution altimeter
systems are more efficient farther from the coast. |
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| Keywords: | North Sea Barotropic dynamic Wide swath ocean altimeter Altimeter constellations Tide gauges Ensemble Kalman Filter |
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