Dynamics of the semi-diurnal and quarter-diurnal internal tides
in the Bay of Biscay. Part 1: Barotropic tides
- Modelling the global ocean tides: modern insights from FES2004
The AMANDES tidal model for the Amazon estuary and shelf.
of the semi-diurnal and quarter-diurnal internal tides in the
Bay of Biscay. Part 1: Barotropic tides
Pairaud I. L., Lyard F., Auclair
F., Letellier T., Marsaleix P.
generation of internal tides in the ocean is due to the interaction
of strong barotropic tidal currents with variable topography
in stratified waters, transferring energy from the external
to the deep ocean. The internal tides feed later the ocean mixing,
playing a major role for the maintenance of the stratification
of the global ocean. A remarkable region in terms of tidal energy
is the European continental shelf. As a first step toward the
study of internal tides in the Bay of Biscay, this paper aims
at understanding the barotropic tides and associated energy
budgets. On continental shelves and in coastal seas the use
of regional models with fine grid resolution is preferred to
the use of global tidal atlases derived from altimetry. The
unstructured grid T-UGOm model is used to compute the NEA-2004
tidal solutions in the North-East Atlantic ocean, with errors
greatly reduced in coastal areas compared with global models.
Energy budgets are discussed based on the inclusion of nonlinearities
in the tidal solutions. The sea surface height and depth averaged
currents are used to compute the tidal energy conversion from
barotropic to baroclinic tides, tidal dissipation and energy
flux. A total amount of energy of 250 GW is found for the M2
tide. The path of M4 energy from the Southern Atlantic ocean
toward the Bay of Biscay is highlighted, advocating for non-zero
boundary conditions in regional models. The 3-dimensional coastal
ocean SYMPHONIE model has been implemented to simulate the surface
tides in the Bay of Biscay. Solutions are validated by comparison
with the NEA-2004 solutions and observations
Modelling the global
ocean tides: modern insights from FES2004
the 1990s, a large number of new tidal atlases were developed,
primarily to provide accurate tidal corrections for satellite
altimetry applications. During this decade, the French tidal
group (FTG), led by C. Le Provost, produced a series of finite
element solutions (FES) tidal atlases, among which FES2004 is
the latest release, computed from the tidal hydrodynamic equations
and data assimilation. The aim of this paper is to review the
state of the art of tidal modelling and the progress achieved
during this past decade. The first sections summarise the general
FTG approach to modelling the global tides. In the following
sections, we introduce the FES2004 tidal atlas and validate
the model against in situ and satellite data. We demonstrate
the higher accuracy of the FES2004 release compared to earlier
FES tidal atlases, and we recommend its use in tidal applications.
The final section focuses on the new dissipation term added
to the equations, which aims to account for the conversion of
barotropic energy into internal tidal energy. There is a huge
improvement in the hydrodynamic tidal solution and energy budget
obtained when this term is taken into account.
Lefevre F., Letellier
T., Francis O.
the global ocean tides: modern insights from FES2004 Ocean
AMANDES tidal model for the Amazon estuary and shelf
AMANDES project aims to study transports from the Andean mountains
to the Atlantic Ocean through the Amazon system. This requires
realistic estuarine modelling in this area strongly forced by
tides and river discharge. As none of the existing models for
this region would fit the actual needs of the project, a specific
new generation model has been implemented. The
model is based on the hydrodynamic finite element model T-UGOm.
In a first step, we limit our investigations to tidal dynamics.
As the Amazon estuary is a very shallow macro-tidal area, it
is necessary to improve the available bathymetries and to develop
a precise bottom friction parametrisation. In this paper, we
discuss the implementation of a high resolution regional model.
This allows us to develop a precise and accurate tidal model:
for instance, the overall root mean square error on complex
differences is reduced from 54 cm in a standard model to 27
cm in our best model. Such precise and accurate tidal modelling
is a prerequisite for modelling particle transport.
More details in: Le
Bars Y., Lyard F., Jeandel
C., Dardengo L., (Ocean Modelling 2010)