the Western English Channel model

The Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) is a finite difference hydrodynamic model developed particularly for the simulation of small scale coastal-ocean processes (e.g. Holt and Proctor, 2003), but has been applied from estuaries to deep ocean domains. It is fully described by Holt and James (2001). It includes an advection scheme (James, 1996) with excellent feature preserving, stability and conservation properties; a sophisticated vertical turbulence model (GOTM, Buchard et al., 1999); and accurate calculations of horizontal pressure gradients. The POLCOMS model has recently been upgraded to the latest version, including a second order dynamic equation of the κ-ε type with a dynamic dissipation rate equation as described in Holt and Umlauf (2008).

Currently, use of high performance computers increases the model speed to about 1000 times that of a desk top machine, which allows high-resolution, long term simulations and the coupling to an ecosystem model as sophisticated as ERSEM (Allen et al., 2001). This coupling is made at the same temporal and spatial resolution as the physics model so the complex 3D interactions between the ecosystem and the hydrodynamics can be directly investigated (Holt et al., 2003). The ERSEM code is a component of the main time stepping loop of the physics code and as such takes the hydrodynamics of temperature, salinity and diffusivity from the physical model.

The WEC1 domain has 254×145 grid points covering the region 50.9 48.48°N / -7.60 -1.25°W, with 32s-levels in the vertical. The horizontal resolution equates to 1/60° in longitude, and 1/60° in latitude. The model has 82 biological state variables; 44 of which are pelagic and the remainder benthic. Phytoplankton is split into four functional sub-groups: diatoms, flagellates, picophytoplankton and dinoflagellates, and each of these are defined in terms of their constituent carbon, nitrogen, phosphate, and silicate where relevant. Similarly, zooplankton is divided into heterotrophic nanoflagellates, microzooplankton and omnivorous mesozooplankton. The model also considers bacteria, dissolved and particulate organic matter and nutrients. Full details of the pelagic submodels can be found in Blackford et al. (2004) and references therein. The benthic model is described in Blackford (1997) and Ruardji and van Raaphorst (1995).

Western English Channel – 7.5875 E to -1.2875 E, 48.4752 N to 50.8752 N

Bathymetry of the Western English Channel domain at 1km resolution

POLCOMS

Hourly

Arakawa B-grid; 1nm x 1nm, 254x145x32 grid points covering the region 50.9 48.48°N / -7.60 -1.25°W

32 s-coordinate vertical levels

NOOS

- Hourly 10m wind and atmospheric pressure from North Atlantic European atmos.Met Office NWP model

- 3-hourly heat and freshwater from Met Office Mesoscale NWP NWP model.

The model is forced at the lateral boundaries with data extracted from an ERSEM-POLCOMS model simulation of the north-west European continental shelf domain (MRCS, 7km resolution), run operationally at the U.K. Met Office. The Met Office MRCS model obtains daily boundary conditions of temperature, salinity, barotropic velocity and sea-surface height from the Met Office Atlantic Margin Model (AMM). Surface forcing is provided from the Met Office’s Mesoscale Numerical Weather Prediction model via three-hourly average fields of penetrating and non-penetrating heat fluxes (corrected for intra-model SST differences by a flux correction term), moisture fluxes, and hourly instantaneous fields of wind speed and surface pressure. The required boundary forcing is daily for the 44 pelagic state variables and the temperature and salinity, for all vertical levels, and hourly for the depth integrated baroclinic u velocity (ub), baroclinic v velocity (vb) and zeta, the change in sea surface height. Boundary data is transferred to PML automatically every day by ftp. The data is further manipulated via automatic scripts for input into the WEC model domain. The original 7km is interpolated to 1nm with spline functions.

Free-slip

Quadratic ‘law of the wall’

No explicit

Piecewise parabolic method

Mellor-Yamada 2.5 with Galperin

Yes

The Functional Group Model (FGM) (ERSEM, Baretta et al., 1995) divides the ecosystem into aggregated groups representing basic functional roles (production, consumption and decomposition) for both the pelagic and benthic systems. These are subdivided into size classes to create a foodweb with five phytoplankton groups, three zooplankton and one bacteria group including a dissolved and particulate detritus pool (Blakford et al., 2004). Physiological processes and population dynamics are described by fluxes of carbon or nutrients between functional groups. ERSEM features include de-coupled Carbon-Nutrient dynamics following a Droop type quota model which allows for luxury storage; a simple relaxation scheme simulates phytoplankton photoacclimatation; and a benthic module describes the recycling of nutrients in a layered benthic substrate and the exchange of nutrients with the pelagic system.

The new version of ERSEM in V1 has a new light formulation that includes three spectral bands; namely blue (400-500nm), green (500-600nm) and red (600-700nm). For the new version, a more accurate description of the downwelling irradiance ( ) was used. To model the approach of Gregg and Carder (1990) modified to include the effects of clouds (Reed, 1977) was used. Irradiances were resolved at each λ in the PAR range and later integrated into the three blue, green and red bands. Diffuse attenuation coefficients for each bands were estimated following Lee et al., (2005). Specific absorptions and backscatter coefficients were obtained from tank experiments carried out in PML with single phytoplankton species cultures.

82 state variables, including: - 4 phytoplankton groups,

- 3 zooplankton groups,

- pelagic bacteria,

- 5 benthic organisms,

- 2 benthic decomposers,

- 2 DOM groups,

- 3 POM groups,

- 5 nutrients,

- oxygen and carbon dioxide.

Simulation of both pelagic and benthic nutrient-phytoplankton-zooplankton-decomposer dynamics using carbon as its basic unit of currency although the cycling of oxygen and the nutrients, nitrogen, phosphorous and silicate are also calculated.

New light formulation includes 3 spectral bands (blue – 400-500nm; green – 500-600nm; and red – 600-700nm) with a more accurate description of the downwelling irradiance.

Met Office MRSC POLCOMS-ERSEM resume writer