Tidal Aggregation for Global Ocean Circulation Models

EDS Newsletter #3: Tidal Aggregation for Global Ocean Circulation Models. The RPS Environmental Data Service (EDS) includes several global ocean circulation models, such as HYCOM, BlueLink and Copernicus. These global operational forecast products provide critical inputs required for our rapid response modeling tools for search and rescue and oil or chemical spills. Although these data products provide global coverage in 1- or 3-hourly timesteps, they lack the tidal forcing and the resolution required to simulate complex coastal zones.

Eric Comerma, Director, International Services
Nathan Benfer, Principal Consultant - Metocean

How to simulate complex coastal zones

For example, a large spill from an offshore platform starts in the open ocean where ocean circulations dominate the movement of oil in the water. However, as the oil slick moves towards the coast, the tidal circulation may influence the oil’s trajectory, potentially driving the oil into estuaries and ports. In some regions in the world, tidal forcing is a key component in the coastal circulation, so it is important to account for it when generating forecasts. Otherwise, it may generate incorrect results and badly impact the decision making process.

There are no operational global ocean circulation models that include tidal currents at higher enough temporal or spatial resolutions to be useful for oil, chemical or search and rescue response modeling for incidents covering both open ocean and coastal zones.

Accordingly, RPS addressed this issue by aggregating on-the-fly, on-demand global circulation models with our own tidal models.

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Figure 1: Example of hydrodynamic grid in the North Sea with zoom in at the Orkney Islands (Scotland).

Advanced modeling solutions

RPS oceanographers implemented a seamless global tidal model generated using our own advanced ocean/coastal hydrodynamic model, HYDROMAP. The model domain is sub-gridded to a resolution of ~500 m for shallow and coastal regions, starting from an offshore (or deep water) resolution of ~1/12°.  The finer grid cells are allocated in a stepwise fashion to resolve flows more accurately along the coastline, around islands and over regions with a complex bathymetry.

The resulting aggregated product covers both the global scale in open ocean and the high resolution for tidal flows in coastal/estuarine environments.

This RPS hybrid product provides the ultimate flexibility to rapidly model oil or chemical spills, or conduct search and rescue modeling in any part of the world. Testing has shown that this product has increased forecast skill compared with global ocean currents or tidal currents used separately.

This hybrid product is operationally available in RPS MAP Apps (SARMAP, OILMAP, CHEMMAP) and a variety of web-based platforms, and it is also used by our in-house 24/7 emergency response modeling services.

For further information about this, or any other of the products and services provided by RPS, please contact EDSSupport@rpsgroup.com

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Figure 2: Example of the Aggregated Global Copernicus current layer in OILMAP. The query is generating a current timeseries for a particular point that shows how tidally dominated the area is at the Orkney Islands (Scotland).

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