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As our reliance upon numerical models for forecasting environmental conditions increases, so does our need to quantitatively analyse their performance. Often, a single metric approach is adopted, the choice of which is dependent upon the application for which the model output are to be used. Here we present a multi-metric verification approach to analyse the spatial and temporal performance of a hydrodynamic ecosystem model. The metrics allow us to investigate the model's ability to predict the inter- and intra-annual spatial variations and are used to evaluate surface chlorophyll-a estimates from the POLCOMS-ERSEM model, using satellite Earth observation data from NASA's MODIS-Aqua sensor. The study focuses on a region of the north east Atlantic which encompasses both open ocean and shelf seas, presenting a sizeable challenge for any model. The metrics reveal that the model is able to capture the mean annual chlorophyll-a signal (as exhibited in the Earth observational data) and has the capability to describe medium scale spatial variations. The seasonal signal exhibited in the Earth observation data is not apparent in the model fields. Possible reasons for the mis-match between the Earth observation and model data are discussed. Notwithstanding these issues, the model exhibits predictive skill during the northern hemisphere summer months for a range of chlorophyll-a concentrations. This multi-metric evaluation approach provides a method for the rigorous evaluation of the spatial and temporal accuracy of the hydrodynamic ecosystem model

We review mechanisms and studies of exchange between the north-east Atlantic and the adjacent shelf sea. Mechanisms include: well-developed summer upwelling and associated filaments off Portugal and north-west Spain giving exchange O(3 m**2/s per unit length of shelf); prevailing westerly winds further north driving exchange O(1 m**2/s); poleward flow along most of the upper slope with associated secondary circulation O(1 m**2/s); meanders and eddies in this poleward flow; eddies shed from slope waters into the Bay of Biscay; local exchanges at shelf spurs and depressions or canyons (e.g. dense-water cascading of order 1 m**2/s). Tidal transports are larger; their reversal every six hours makes exchange largely ineffective except where internal tides are large and non-linear, as in the Celtic Sea where solitons carry water with exchange O(1 m**2/s). These various physical exchanges amount to an estimated 2-3 m**2/s per unit length of shelf, between ocean and shelf; a numerical model estimate is comparable: 2.5 x 106 m**3/s onto and off the shelf from Brittany to Norway. Mixing controls the seasonal thermocline, affecting primary production and hence fluxes and fate of organic matter. Specifically, CO2 take-up by primary production, settling below the thermocline before respiration, and then off-shelf transport, make an effective shelf-sea “pump” (for CO2 from the atmosphere to the deep ocean). However, knowledge of biogeochemical fluxes is generally sparse; there is scope for more measurements, model validation and estimates from models.

The role of the North Atlantic Oscillation (NAO) in effecting changes in winter extreme high and low waters and storm surges in UK waters has been investigated with the use of a depth-averaged tide+surge numerical model. Spatial patterns of correlation of extreme high and low waters (extreme still water sea levels) with the NAO index are similar to those of median or mean sea level studied previously. Explanations for the similarities, and for differences where they occur, are proposed. Spatial patterns of correlations of extreme high and low and median surge with the NAO index are similar to the corresponding extreme sea-level patterns. Suggestions are made as to which properties of surges (frequency, duration, magnitude) are linked most closely to NAO variability. Several climate models suggest higher (more positive) average values of NAO index during the next 100 years. However, the impact on the UK coastline in terms of increased flood risk should be low (aside from other consequences of climate change such as a global sea-level rise) if the existing relationships between extreme high waters and NAO index are maintained

The Met Office has run a 3-D circulation model of the NW European shelf seas in the daily suite of operational forecast models since June 2000, using the POLCOMS system implemented on a ~12 km grid, providing a nowcast and 2-day forecast. Inside this model are nested regional models of the Irish Sea region, at one nautical mile resolution, and the NW European Shelf to the 200 m contour (Medium Resolution Continental Shelf, MRCS), at ~6 km resolution, that were introduced in 2003 and early 2005, respectively. The MRCS model includes a basic representation of sediment transport. In addition, a coupled physical-ecological model on the MRCS domain using the POLCOMS-ERSEM system is running pre-operationally in near real time and is coupled to a fuzzy-logic based system to estimate risk of harmful algal blooms (HAB). A constant-density relocatable model can be applied in high resolution to any region of the shelf seas. Data from the models are available either via the Met Office Data and Products Distribution Service for operational purposes, or on request via ftp for research collaborations, and have been provided to many international research groups and projects. Modelled surface currents and winds have been used to force the VISAR and SARIS Search and Rescue (SAR) and OSIS Oil drift packages. Sediment and biogeochemical parameters from the ecological model are used to provide estimates of visibility. We focus on model validation and highlight areas where the models could be improved. Comparison with SST observed by moored buoys, the daily GHRSST Ocean Surface Temperature and Ice analysis (OSTIA) product and monthly temperature climatology indicate good agreement for the annual cycle of sea surface temperature in the North Sea and Irish Sea. However, in the continental margin region to the west of the UK there is a significant temperature deficit in the NW European Shelf model. This appears to result from errors in the simulation of the along-slope current that can be