Ocean forecast models
Dansk version


DMI ocean forecast models
The DMI ocean models calculate:

Ocean models are forced by the weather forecast, as produced by a



Model domains
DMI ocean model are regional: they cover a limited body of water. Global metocean models are run at ECMWF, Reading, England.

Focus areas are:

  • North Sea - Baltic Sea
  • Danish Waters
  • Greenland Waters

In addition, DMI produces ocean forecasts for the Arctic, the Mediterranean, the Yellow Sea, the Red Sea, the Irish Sea, the Norwegian Coast and the North Atlantic.

DMI sets up local (small-scale) and regional models as required.

Forecasts
Ocean forecasts are valid for the upcoming 2½-10 days, depending on model type and domain.

Publicised at DMI web sites (most in danish):

You will find hourly maps of ocean conditions. The data is valid on grid points, separated by some kilometers. 2-dimensional parameters (sea level, sea ice, waves) are shown as surface maps. 3-dimensional parameters are mapped at a number of depth levels. Locations with some kind of recording equipment will have time series displayed.

Model output is stored on tape in GRIB (GRid In Binary) format. Table

Atmospheric model
The backbone of all ocean forecasting is a numerical weather prediction (nwp) model. The nwp provides the surface forcing - mechanic, thermodynamic and radiative - that sets the ocean in motion and changes its physical and chemical state.

DMI-Hirlam forecasts range 2½ days ahead. DMI-Hirlam covers the North Sea - Baltic Sea in 3km resolution, and a large part of the North Atlantic, including the Arctic Sea and the Mediterranean, in 15 km resolution. Other sub-domains cover the Caspian Sea, the Red Sea, and the Yellow Sea.

Global ECMWF forecast are valid 10 days ahead. They are produced at the european center in Reading, England. ECMWF forecasts supplement DMI-Hirlam where required, but the time/space resolution is coarser.

No weather forecast is perfect, and the errors are carried over into the ocean forecast. Given an ocean model, the best possible forecast is produced using analysed weather maps, where observed weather and weather model are combined to minimise the error. All weather forecasts start out with an analysis. Hirlam is re-analysed every 6 hours, ECMWF every 12 hours.

Circulation/hydro-dynamical models
A hydro-dynamical model describes the motion of water bodies, represented by sea current and sea level. A complete hydrographic description include sea temperature, salinity, and sea ice.

HBM is a nested 3-dimensional ocean model developed at the Bundesamt für Seeschiffahrt und Hydrographie, Hamburg, Germany. It was earlier designated BSHcmod. It has been used in Germany since 1995, at DMI since 2001. Originally constructed specifically for the North Sea - Baltic Sea, HBM is today a general model, in principle applicable to any model region. Until now it has only been used in shallow-water, regional areas, e.g. the Northwest European Shelf Seas.

HYCOM-CICE is a 3-dimensional ocean model coupled with a sea-ice model. Both models are developed in Miami/Los Alamos, USA. DMI has set up HYCOM-CICE for the the North Atlantic north of 20°N, including the Arctic Sea and the Mediterranean. Hycom is well suited for large-scale modelling, with the possibility to zoom in on small domains.

Storm surge models
DMI uses the 3-dimensional model HBM for sea level / storm surge predictions. A storm surge model calculates the sea level. This can be done with a 3-dimensional hydro-dynamic model, or with a more simple 2-dimensional model. A 2-d model has only one vertical layer, so that the current velocity has no vertical structure. In some regions, e.g. the North Sea, this is close to reality. In strafied regions, e.g. the Transition Area, surface and bottom current may be very different. In such regions, a 3-d model gives better sea level predictions.

The DMI storm surge model covers the entire North Sea - Baltic Sea. It calculates sea level variations along the Danish coast, with a durance up to about a week. These depend on the weather (strong wind events), and the Atlantic tide.

Wave model
DMI-WAM is based on the spectral 3rd generation wave model WAM Cycle 4.5 developed in the late 1980'ies by the SWAMP modelling group. WAM calculates wind-generated waves in open waters, outside the breaker zone. It has been used at DMI since 1999. DMI-WAM covers the North Atlantic north of 30°N, with bordering seas

Drift model
BSHdmod calculates drifting objects, spreading of dissolved substances, and oil drift and weathering. BSHdmod is an add-on module to the hydro-dynamical model HBM, and was also developed at the Bundesamt für Seeschiffahrt und Hydrographie, Hamburg, Germany, specifically for the North Sea - Baltic Sea. DMI has generalised BSHdmod, to it may be combined with other ocean models, and used in other regions.

Hycom also comes with a drift module. It is used to calculate drift of fry in Greenland waters, icebergs, .. .

Ecological model
A coupled ERGOM/HBM model is under development, in collaboration with the National Environmental Research Institute (NERI) and the Danish Fisheries Research Institute (DFRI). ERGOM is developed at Institut für Ostseeforschung in Warnemünde. It calculates the content of oxygen, nutrient and a number of plankton/algae types in sea water.

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Jacob Woge Nielsen - December 17th 2012