Assessment and development of a sediment model within an operational system

The Medium Resolution Continental Shelf (MRCS) modeling system is a coupled hydrodynamic plus sediment (POLCOMS) and ecosystem (ERSEM) model covering the UK shelf region. It is run operationally at the Met Office providing daily analyses and 5-day forecasts for a variety of fields. The output of the sediment model within the MRCS system has been assessed against CEFAS SmartBuoy turbidity data and satellite-retrieved surface sediment concentration for the period 2008 to 2009. The results of the assessment showed poor variability throughout the year highlighted by low correlations and large differences in standard deviations between the model and observations. In light of these results, the sediment model parameterizations for the mechanisms of erosion, deposition and settling were modified and the model was further developed by incorporating an aggregation/disaggregation scheme. The initialization method was also reviewed and updated. Assessment of this collection of developments showed significant improvements in variability as well as improvements in the quantitative match to the observations. Improvements were seen in correlations, mean values, standard deviations and percent differences throughout the assessment period. As a result of sensitivity studies it was found that each of the model developments had different impacts on improving the model predictions. All the model developments had a quantitative impact on the predicted surface sediment concentration with the aggregation acting to constrain the increase in sediment brought about by the erosion and settling. The changes in erosion and settling predominantly accounted for the improvement in correlation between the model and satellite observations.