NE Atlantic and NW European Continental Shelf

Sea level; Bathymetry and Elevation

Inapplicable

Objective To generate a long-term data set of model sea levels and analyse this to understand aspects of sea-level change and variability. Components: 1. Model runs A unique gridded model data set has been created and is periodically updated providing long-term (1955 to date) sea level, tide and surge elevations and depth-averaged currents over an extensive area. Two-dimensional tide-surge models have been run with 35km resolution. The first (CSX) covers the NW European continental shelf and the second (NEAC) also covers the shelf but extends into the NE Atlantic. The models have been forced by a meteorological data set provided by the Norwegian Meteorological Institute (DNMI). This comprises gridded ( approx 75km resolution) 6-hourly MSLP and derived wind components from the routine meteorological analyses. For each year, two model runs have been done; one for tide only and the other for tide plus meteorological forcing, which allows the calculations of surge residuals including tide-surge interaction , an important process in shallow water. The model data set is extended whenever the meteorological data becomes available from DNMI. Surge elevations from the model have been compared to historical data sets of observed surges for validation. Statistical analysis shows an accuracy of order 10cm (RMS) in surge elevations, which is comparable to that obtained by the Operational Storm Surge Model. Depth-averaged currents have also been compared with observations. 2. Application of the data Analysis of these runs has been undertaken in various research projects. Some examples are given below: Extreme value analysis has been performed on the entire data set. This provides a statistical probability distribution of surge excedence levels, which defines the present day surge climate - an important reference for climate change studies. Analysis of seasonal sea-level variability has included the calculation of the long-period tidal components, Sa and Ssa, which have significant inter-annual variability - important e.g., for interpreting surge forecasts. Long-term means have been calculated in some studies, e.g., surge and sea level; and mean volume fluxes have also been calculated for strategic transects of the shelf. The data set has also been analysed for some longer-term components of sea level. For example, the anomalous Pole Tide, which is caused by Chandler Wobble and has a period of approx 14 months, was shown to be forced by the meteorology in the North Sea. Data are available from POL Applications Group. Funding Funding for the model runs and analyses was provided by: EU (STOWASUS-2100; WASA; NOWESP) MAFF (Climex; CDV2075; Seasonal Variations) POL Principal Investigators Dr Roger Flather Jane Williams POL's and BODC's roles BODC provide observed surge data from the National Tide Gauge Network each month for model validation; POL tidal analysis experts provide tidal analysis/predictions and observed turning point values when necessary.

Proudman Oceanographic Laboratory
Joseph Proudman Building 6 Brownlow Street
Liverpool
Merseyside
L3 5DA
United Kingdom