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| Titel |
Coupling of WRF meteorological model to WAM spectral wave model through sea surface roughness at the Balearic Sea: impact on wind and wave forecasts |
| VerfasserIn |
R. Tolosana-Delgado, A. Soret, O. Jorba, J. M. Baldasano, A. Sánchez-Arcilla |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065542
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| Zusammenfassung |
| Meteorological models, like WRF, usually describe the earth surface characteristics by
tables that are function of land-use. The roughness length (z0) is an example of
such approach. However, over sea z0 is modeled by the Charnock (1955) relation,
linking the surface friction velocity u*2 with the roughness length z0 of turbulent air
flow,
z0 = α-u2*
g The
Charnock coefficient α may be considered a measure of roughness. For the sea surface, WRF
considers a constant roughness α = 0.0185. However, there is evidence that sea surface
roughness should depend on wave energy (Donelan, 1982). Spectral wave models
like WAM, model the evolution and propagation of wave energy as a function of
wind, and include a richer sea surface roughness description. Coupling WRF and
WAM is thus a common way to improve the sea surface roughness description of
WRF. WAM is a third generation wave model, solving the equation of advection
of wave energy subject to input/output terms of: wind growth, energy dissipation
and resonant non-linear wave-wave interactions. Third generation models work on
the spectral domain. WAM considers the Charnock coefficient α a complex yet
known function of the total wind input term, which depends on the wind velocity
and on the Charnock coefficient again. This is solved iteratively (Janssen et al.,
1990).
Coupling of meteorological and wave models through a common Charnock coefficient is
operationally done in medium-range met forecasting systems (e.g., at ECMWF) though the
impact of coupling for smaller domains is not yet clearly assessed (Warner et al, 2010). It is
unclear to which extent the additional effort of coupling improves the local wind and wave
fields, in comparison to the effects of other factors, like e.g. a better bathymetry and relief
resolution, or a better circulation information which might have its influence on local-scale
meteorological processes (local wind jets, local convection, daily marine wind regimes,
etc.).
This work, within the scope of the 7th EU FP Project FIELD_AC, assesses the impact of
coupling WAM and WRF on wind and wave forecasts on the Balearic Sea, and compares it
with other possible improvements, like using available high-resolution circulation
information from MyOcean GMES core services, or assimilating altimeter data on the
Western Mediterranean. This is done in an ordered fashion following statistical design rules,
which allows to extract main effects of each of the factors considered (coupling, better
circulation information, data assimilation following Lionello et al., 1992) as well as
two-factor interactions. Moreover, the statistical significance of these improvements can be
tested in the future, though this requires maximum likelihood ratio tests with correlated
data.
Charnock, H. (1955) Wind stress on a water surface. Quart.J. Row. Met. Soc. 81:
639-640
Donelan, M. (1982) The dependence of aerodynamic drag coefficient on wave
parameters. Proc. 1st Int. Conf. on Meteorology and Air-Sea Interactions of teh
Coastal Zone. The Hague (Netherlands). AMS. 381-387
Janssen, P.A.E.M., Doyle, J., Bidlot, J., Hansen, B., Isaksen, L. and Viterbo, P. (1990)
The impact of oean waves on the atmosphere. Seminars of the ECMWF.
Lionello, P., Günther, H., and Janssen P.A.E.M. (1992) Assimilation of altimeter data
in a global third-generation wave model. Journal of Geophysical Research 97
(C9): 453–474.
Warner, J., Armstrong, B., He, R. and Zambon, J.B. (2010) Development of a Coupled
Ocean-Atmosphere–Wave–Sediment Transport (COAWST) Modeling System.
Ocean Modelling 35: 230–244. |
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