DMI operates a regional 3D ocean model HBM for the North Sea - Baltic, in order to provide information about the physical state of the Danish and nearby waters in the near future. The Figure to the right shows model domain and water depth for the 3D grid.

Calculations are carried out at a number of fixed depths, from surface to sea bed. Sea ice is described by extent,m concentration and thickness. A marine ecology module may be coupled.

The HBM code was developed in the early 1990'ies at Bundesamt für Seeschifffahrt und Hydrographie (BSH) in Hamburg, Germany. At the time the model was known as BSHcmod. It has undergone extensive revision in the DMI implementation, in co-operation between DMI and BSH. Basically the same code is used in the Baltic HIROMB co-operation.

Three types of input is applied: surface fields, point sources, and open boundary conditions. Heat flux through the sea bed is parameterized. HBM is forced by DMI's numerical weather prediction (nwp) model Harmonie. Any nwp model capable of providing the same parametre may in priciple be used. The following parameters are used:

• 10 metre wind speed and direction
• mean sea level atmospheric pressure
• surface (2 metre) air temperature
• surface air (2 metre) humidity
• cloud cover

HBM calculates surface energy fluxes (mechanical, radiative, thermodynamic) using bulk parameterisation formulae. NWP fluxes are thus not used, even if provided, but recalculated ny HBM.
Point source data are

• freshwater fluxes from 846 rivers and diffusive coastal sources
  • obtained from a swedish hydrological model
  • climatology for each calendar day
  • annual climatology
• nutrient from the same rivers (optional)

Open boundary data are:

• tidal sea surface elevation
• monthly climatological hydrography

HBM optionally assimilates one or more types of observered or modelled data:

• sea surface temperature from satellite
• vertical profiles of hydrography
• daily open boundary hydrography data

This facility has not been put in operational use as of yet.

HBM runs every 6 hours, i.e. 4x/day. A run produces a 5 day forecast of the 3-dimensionelle state of the ocean.

HBM calculates, at 15 min.intervals

• sea level
• water temperature
• salinity
• ocean currents
• ice thickness and concentration

Temperature, salt and current is calculated for the entire water column, top to bottom, at ~ 50 fixed depth levels. Sea level at selected, coastal points is calculated in 10 minute time resolution.

Output in high time resolution is intended for internal use. For external use, hourly data is provided.

Output parameter table.

The HBM model set-up consists of 7 model domains:

• NOAMOD - 2-dimensional mesocale model, that calculates sea level as a function of wind speed and air pressure. Generates boundary data (external surge) for the regional 3-dimensionan model
• North Sea - Baltic Sea - 3-dimensional regional model with subdomains
• Transition Area - high resolution model of the waters south of Skagen and west of Bornholm
• Wadden Sea - high resolution model of the German Bight
• Roskilde/Isefjord - high resolution fjord model (nested since 2019)
• Limfjord - high resolution fjord model (nested since 2021)
• Lillebælt - high resolution Little Belt model (nested since 2021)

Model	NOAMOD	HBM North Sea - Baltic Sea	HBM Transition Area	HBM Wadden Sea	HBM Roskilde/Isefjord	HBM Limfjord	HBM Lillebælt
Spatial resolution	6' lat 10' lon (6 n.m.)	3' lat 5' lon (3 n.m.)	30" lat 50" lon (0.5 n.m.)	1' lat 1'24" lon (1 n.m.)	10" lat 10" lon (0.15 n.m.)	6" lat 10" lon (0.1 n.m.)	10" lat 10" lon (0.2 n.m.)
Vertical layers	1	50	52	24	10	21	42
Max. top layers thickness	900m	8m	2m	8m	2m	2m	2m
Time step: Barotropic Baroclinic: Ice	15s - -	20s 90s 900s	10s 90s 900s	20s 90s 900s	5s 15s 900s	2.5s 20s 900s	5s 20s 900s
Atm. forcing	ECMWF GLM	Harmonie NEA ECMWF GLM	Harmonie NEA ECMWF GLM	Harmonie NEA ECMWF GLM	Harmonie NEA ECMWF GLM	Harmonie NEA ECMWF GLM	Harmonie NEA ECMWF GLM
Area: longitude	21W-13E	4.1W-30.3E	9.3E-14.8E	6.2E-10.5E	11.6E-12.1E	8.2E-10.3E	9.5E-10.1E
Area: latitude	48N-66N	Baltic Sea: 48.5N-65.9N North Sea: 48.5N-59N	53.6N-57.6N	53.2N-55.7N	55.6N-56N	56.5N-57.1N	55.2N-55.7N
Open boundaries	Radiation condition	1. Surge contribution from NOAMOD 2. Tidal sea level based on 17 constituents 3. Monthly climatology fields for T and S via a sponge layer	nested with regional model	nested with regional model	nested with transition area model	nested with regional and transition area model	nested with transition area model