En:parameterization tuning

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Parameterization tuning

The baseline to be improved on is the TEST441b parameterization as described in Ardhuin et al. (JPO 2010). Occasionally some reference will be made to “BAJ” (Bidlot et al. 2005) because it is used at ECMWF and elsewhere: BAJ is also know as WAM Cycle 4.5.

Filipot et al. (submitted to Ocean Modelling) have produced a TEST500 that has some important physical improvements on TEST441b : namely the “spontaneous breaking” is not purely local in frequency and it uses a wave breaking probability. Yet TEST500 still has some deficiencies (the relative dissipation Soc/E is isotropic in directions for the spontaneous part, contrary to TEST441b, and the breaking probabilities are underestimated from mature waves). We are now working on variants from TEST500 (TEST5xx) that will improve TEST500 to make it better than TEST441b for all conditions.

Tuning strategy

The reference runs include, in this order:

  • A 1-point uniform ocean run at 10 m/s to verify full development limit: the dissipation constant and gustiness parameter ZALP are tuned with this
  • the SHOWEX case hindcast (slanting fetch limited growth) to adjust the directional properties
  • a global 0.5° 1-year hindcast. At present we focus on year 2008 which is the more recent year (i.e. with the best available winds) for which we also have iceberg distributions.
  • The DUCK94 and Terscheling data for the surf zone to adjust the deep vs shallow dissipation rate transition

This global 0.5° run is analyzed in a variety of ways: