Transition of Operational Modelling of the North West European Shelf, From POLCOMS to NEMO, a Nucleus for European Modelling of the Ocean.

The European operational ocean modelling community is embarking on a collaborative project which aims to bring together expertise from European research institutions and operational centres alike, into a unified ocean modelling framework called the Nucleus for European Modelling of the Ocean (NEMO). NEMO is based on a deep ocean model thus the development of operational ocean basin scale models are at advanced stage and live. The Met Office is transitioning from a tried and tested 3D operational shelf seas model, the Proudman Oceanographic Laboratory Coastal-Ocean Modelling System (POLCOMS) to an operational implementation of NEMO for the North West European Shelf. POLCOMS replacement by NEMO at the Met Office allows for convergence of ocean model systems across the office from basin scale and coastal scale forecast modelling to climate scale modelling under a unified system. In order for NEMO to work as an effective shelf seas model a number of shelf specific modules needed to be added and modified, including a non linear free surface, tidal forcing at the open boundaries, sigma and s-coordinates, horizontal pressure gradient correction schemes, surface boundary forcing, riverine inputs, etc. The model is being validated against a dense array of in situ measurements on the North West European shelf, satellite derived measurements, hindcast runs of the present operational POLCOMS model and a highly tuned 2D surge specific model. Open boundary conditions for salinity, temperature, sea surface height, baroclinic and barotropic velocities are provided by a deep ocean version of NEMO for the North Atlantic Ocean. Surface fluxes are taken from the operational NWP model at the Met Office. It is envisaged that NEMO shall incorporate assimilation in the shelf seas model, assimilation is currently implemented using the Forecasting Ocean Assimilation Model (FOAM) in the open ocean versions of NEMO.