North Sea - Baltic Sea ocean model
HBM
Dansk version

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.

Model code
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.

Input
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
  • nutrient from the same rivers (optional)
Open boundary data are:
  • tidal sea surface elevation
  • monthly climatological hydrography

Data-assimilation
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.

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

Output
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.

Model set-up
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

Jacob Woge Nielsen - Mar. 29th 2022