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| Gravity Waves | Modelling | Model Outputs Analysis | Coastal Altimetry | 3D Circulations | Sediment transport, Ecology | Data Assimilation |
Wavelet Analysis: Coastal
ocean numerical modeling is basically the representation
of the dynamics of the coastal ocean in a chosen range of length scales
and over an associated frequency band, including the modeling of both
coherent processes and associated transient processes. The ocean dynamical
features can be individually identified by combining wavelet analysis
for time and frequency localization and principal component analysis
to "decorrelate" physically consistent structures. In the
present study, the so-called WEof analysis is applied for the extraction
of external gravity waves and internal gravity wave lower modes in
a simple case of a flat bottom, constant Brunt-Väisälä
ocean. It is shown that, with some well known restrictive assumptions,
WEof analysis is an efficient candidate for the recognition of frequency
localized dynamical processes.More details in: Pairaud I., Auclair F., 2005. Combined wavelet and principal component analysis (WEof) of a scale oriented model of coastal ocean gravity waves Dynamics of Atmospheres and Ocean. 40, 254-282 doi:10.1016/j.dynatmoce.2005.06.001 |
Forecast Error Analysis: The
probability density function (pdf) of forecast errors due to several
possible error sources is investigated in a coastal ocean model driven
by the atmosphere and a larger-scale ocean solution using an Ensemble
(Monte Carlo) technique. An original method to generate dynamically
adjusted perturbation of the slope current is proposed. The model
is a high-resolution 3D primitive equation model resolving topographic
interactions, river runoff and wind forcing. The Monte Carlo approach
deals with model and observation errors in a natural way. It is particularly
well-adapted to coastal non-linear studies. Indeed higher-order moments
are implicitly retained in the covariance equation. Statistical assumptions
are made on the uncertainties related to the various forcings (wind
stress, open boundary conditions, etc.), to the initial state and
to other model parameters, and randomly perturbed forecasts are carried
out in accordance with the a priori error pdf. The evolution of these
errors is then traced in space and time and the a posteriori error
pdf can be explored. Third- and fourth-order moments of the pdf are computed to evaluate the normal or Gaussian behaviour of the distribution. The calculation of Central Empirical Orthogonal Functions (Ceofs) of the forecast Ensemble covariances eventually leads to a physical description of the model forecast error subspace in model state space. The time evolution of the projection of the Reference forecast onto the first Ceofs clearly shows the existence of specific model regimes associated to particular forcing conditions. The Ceofs basis is also an interesting candidate to define the Reduced Control Subspace for assimilation and in particular to explore transitions in model state space. We applied the above methodology to study the penetration of the Liguro-Provençal Catalan Current over the shelf of the Gulf of Lions in north-western Mediterranean together with the discharge of the Rhône river. This region is indeed well-known for its intense topographic and atmospheric forcings. More details in: Auclair F., Marsaleix P., and De Mey P., 2003. Space-time structure and dynamics of the forecast error in a coastal circulation model of the Gulf of Lions. Dynamics of Atmospheres and Oceans, 36, 309-346. doi:10.1016/S0377-0265(02)00068-4 |