National Oceanography Centre Liverpool national capability POLCOMS 1964 - 2004 simulations information document
Background
The Natural Environment Research Council (NERC) funds National capability (NC) to enable the UK to deliver world-leading environmental science, support national strategic needs, and respond to emergencies. This includes the research and development activities which keeps this capability at the cutting edge. The National Oceanography Centre (NOC) is responsible, on behalf of NERC, for managing marine science national capability to support the marine science base long-term.
As part of work on NERC national capability, the NOC Shelf and Coastal Impacts team in the Marine Systems Modelling Group used the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) to derive potential temperature, salinity, sea surface height and both baroclinic and barotropic currents for the Atlantic margin of the northwest European shelf, from 1960 to 2004. These data were generated as part of research looking at multi-decadal trends and variability in temperature over the northwest European continental shelf (Holt et al. , 2012).
The dataset consists of
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25 hour average east and northward velocity components (m s -1 ), depth averaged, and for each model depth level across the model domain
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25 hour average potential temperature (°C) and salinity for each model depth and sea surface height (m) across the model domain
The model simulation started at 00:00 UTC 01 January 1960 and finished at 24:00 UTC 31 December 2004.
Simulation details
The information presented here is compiled from sections of Holt et al. (2012) and Wakelin (2013, pers. comm ) and has been confirmed by the Data Originator.
The Atlantic Margin application (AMM) of POLCOMS has been run operationally by the UK Meteorological Office since 2002, using a 1/9° latitude by 1/6° longitude grid with 40 s-coordinate levels in the vertical. This results in cell resolutions varying from 7.860 km to 14.177 km in the x-axis and 12.348 km in the y-axis. The geographic coverage of the AMM simulations are longitude 19.9167°W to 13°E, and latitude 40.0556°N to 64.8889°N. For this NC study, AMM is run for 1960 as a spin-up (from rest with initial temperature and salinity fields from the global ocean model used for boundary conditions, described below), followed by a 45-year integration for the period 1960 to 2004. Years 1960 to 1963 are not included in the dataset as AMM was continuing to spin up from the initial state. The AMM application was run on HECToR, the UK National Supercomputing Service.
The implementation of POLCOMS is described by Wakelin et al. (2009), except for details of the forcing. This was provided by the European Centre for Medium Range Weather Forecasts (ECMWF) 40 year Re-analysis (ERA40) meteorological data for surface fluxes calculated from Coupled Ocean Atmosphere Response Experiment (COARE) v3 bulk formulae (Fairall et al. , 2003). Data were available at 6 hourly intervals, except for precipitation and short-wave radiation, which were daily (the latter modulated by the diurnal cycle). The ERA40 re-analysis ran until September 2001 and in a similar fashion to Brodeau et al. (2010), operational ECMWF data were used to extend the series to 2004.
Open ocean boundary conditions were taken from a run of the global ORCA1 application of the Nucleus for a European Model of the Ocean (NEMO) run from 1958 to 2004 (Smith and Haines, 2009). This forcing model included temperature and salinity profile assimilation and imposed the limit on the simulation period (to finish in 2004). Tidal forcing was provided by 15 tidal constituents from a northeast Atlantic tidal model (Flather, 1981), and tide generating forces were applied across the model domain. Sea surface elevation and depth mean currents (tides at the model timestep and 5-day mean non-tidal currents from ORCA1) were applied using a flux/radiation scheme. Temperature and salinity profiles were relaxed to 5-day mean values from the ORCA1 global model in a four grid cell wide boundary relaxation zone (a baroclinic radiation scheme was not used in this model).
For freshwater fluxes, daily discharge data for 322 rivers were used from the Global River Discharge Data Base (Vörösmarty et al. , 2000) and from data prepared by the Centre for Ecology and Hydrology as used by Young and Holt (2007). In this simulation, gauged discharge data (with UK discharges corrected for ungauged flows (Marsh and Sanderson, 2003)) was used where available; the gaps being filled by a mean annual cycle for each river. A mean annual cycle of volume flow and salinity taken from Danish Hydrographic Institute DYNOCS experiment was used to describe the flow of low salinity water from the Baltic.
The simulation timesteps were 20 seconds for the barotropic currents and 300 seconds for the baroclinic currents. Hourly snapshots were averaged into 25 hour means, in order to remove tidal effects.
Comments
Please be aware that the data are stored by BODC in the state they were supplied by the Data Originator. No quality control or assessments of the data have been undertaken and any interested parties should use the data at their own risk.
References
Brodeau, L., Barnier, B., Treguier, A-M., Penduff, T., Gulev, S., 2010. An ERA40-based atmospheric forcing for global ocean circulation models. Ocean Modelling, 31 (3 - 4), 88- 104.
Fairall, C.W., Bradley, E.F., Hare, J.E., Grachev, A.A., J.B. Edson, J.B., 2003. Bulk parameterization of air-sea fluxes: updates and verification for the COARE algorithm. Journal of Climate, 16, 571 - 591.
Flather, R.A., 1981. Results from a model of the northeast Atlantic relating to the Norwegian Coastal Current. In: Saetre, R., Mork, M. (Eds.), The Norwegian Coastal Current, vol. 2, pp. 427 - 458.
Holt, J., Hughes, S., Hopkins, S., Wakelin, S.L., Holliday, N.P., Dyed, S., González-Polae, C., Saetre Hjøllof, S., Arne Mork, K., Nolan, G., Proctor, R., Read, J., Shammon, T., Sherwin, T., Smyth, T., Tattersall, G., Ward, B., Helen Wiltshire, K.H., 2012. Multi-decadal variability and trends in the temperature of the northwest European continental shelf: A model-data synthesis. Progress in Oceanography, 106, 96-117, http://dx.doi.org/10.1016/j.pocean.2012.08.001.
Marsh, T., Sanderson, F., 2003. Derivation of daily outflows from Hydrometric Areas. National River Flow Archive. Unpublished manuscript.
Smith, G., Haines, K., 2009. Evaluation of the S(T) assimilation method with the Argo dataset. Quarterly Journal of the Royal Meteorological Society, 135, 739 - 756.
Vörösmarty, C.J., Fekete, B.M., Meybeck, M., Lammers, R., 2000. A simulated topological network representing the global system of rivers at 30-minute spatial resolution (STN-30). Global Biogeochemical Cycles, 14, 599 - 621.
Wakelin, S.L., 2013. Personal communication to BODC on grid resolution of AMM simulations.
Wakelin, S.L., Holt., J.T., Proctor, R., 2009. The influence of initial conditions and open boundary conditions on shelf circulation in a 3D ocean-shelf model of the North East Atlantic. Ocean Dynamics, 59, 67 - 81, http://dx.doi.org/10.1007/s10236-008-0164-3.
Young, E.F., Holt, J.T., 2007. Prediction and analysis of long-term variability of temperature and salinity in the Irish Sea. Journal of Geophysical Research, 112, C1, http://dx.doi.org/10.1029/2005JC003386.
