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Baltic Earth

7th Study Conference
Öland, Sweden
10 - 14 June 2013

Conference on Climate Change in the Southern Baltic region
Szczecin, 12-15 May 2014

21st Century Challenges in Regional Climate Modelling
Lund, 16-19 June 2014


BRIDGE - The Main BALTEX Experiment

A bridge connects separated matters and surmounts obstacles

BRIDGE is the Main Baltic Sea Experiment. It took place from March 1999 to March 2001, the first six months being the pilot phase and the remaining 18 months being the basic research phase. This page presents a summary description of BRIDGE as it was presented in 1997. For a comprehensive and detailed description of BRIDGE, the "Strategic Plan" from October 1997can be downloaded here. The processing and analysis of BRIDGE results is still ongoing. One major motivation of BALTIC GRID is the synthesis of BRIDGE.

BRIDGE is expected to

  • fill gaps in our knowledge on water and energy cycles in the Baltic Sea catchment region,
  • bridge existing gaps between meteorology, hydrology and oceanography,
  • build bridges between modellers and experimentalists,
  • join research institutions and national Services in more than 10 countries around the Baltic Sea,
  • foster research co-operation across the Baltic Sea,
  • link basic research and operational applications.


The two outstanding aspects of the experiment are the effective use of all relevant observational material and the use of meteorological, oceanographic and hydrological models. The purpose of the experiment is to aid access to all observations made in the study area and to enhance the use of new experimental data. Observational networks are encouraged to perform at their maximum capacity which will require additional resources from participating institutions. Another purpose is to develop the performance of the meteorological, oceanographic and hydrological models. This will take place especially through concentrating on better coupling of these models, which is a new desired aspect. Important parameters at the interfaces of the model domains are such as soil moisture, snow cover, sea surface temperature, sea ice, surface fluxes, precipitation and river runoff. The correct treatment of the processes involved with these parameters is seen to be very important and yielding a better usability of all models considered here. This is one the major highlights of the experiment. Another basic benefit from the experiment will be the enhancement of the scientific research as a remarkable amount of good quality analysed and assimilated data will be available together with the up-to-date models.



  • to generate comprehensive data sets for process understanding and budget studies to meet BALTEX objectives
  • to concentrate on one unique time period
  • to effectively use relevant observations (planning beforehand !)
  • to use latest versions of coupled models with emphasis on the interfaces of model domains



To generate independent 4-dimensional data sets for the BALTEX region based on

  • delayed-mode 4DDA runs
  • coupled models
  • in situ and remote sensing data from operational and speci-fic networks
  • monitoring activities at specific sites
  • field experiments and process studies


Activities during BRIDGE will be divided into

  • base-line observational and modelling programs to be conducted continuously during the entire 27 months period, and
  • specific enhanced observational and modelling programs confined to limited periods (EOPs) of typically a few weeks or months.

Base-line activities during BRIDGE :

  • 4DDA runs, three different independent systems at different institutions,
  • continuous model runs (both coupled and stand alone modes),
  • operational networks and distribution activities (e.g. GTS),
  • special efforts to collect supplementary relevant data from existing networks in order to increase observational densities in the entire BALTEX region as exemplified during the PIDCAP period,
  • special observational activities which are conducted regularly, either permanently or at special observing dates (e.g. hydrographic measurements on research vessel cruises to be done regularly several times per year, or continuous monitoring activities at specific sites such as Östergarnsholm, Lindenberg, Sodankylä).

Existing networks are suggested to be enhanced for the BRIDGE period. Examples include additional rawinsonde and radar stations.

Enhanced time-limited actions during BRIDGE (EOPs)

  • high-resolution, non-hydrostatic atmospheric model runs for the entire BALTEX region, or specific sub-basins,
  • coupled model runs which are too time-consuming for continuous applications during the base-line period,
  • specific field campaigns of limited duration (such as LITFASS, PEP, DIAMIX or RV cruises) to provide high-quality observational data, which are needed in process-oriented studies,
  • special efforts to enhance observational data densities for the entire BALTEX region (e.g. to increase the density of radiosonde observations).


Observational Requirements

  • Six-hourly radio soundings from stations immediately bordering the Baltic Sea.
  • Additional radiosonde stations on Gotland, Åland and Bornholm during BRIDGE.
  • Collection of all available hydrological information from the whole study area in a timely way.
  • Continuous measurement of temperature, salinity and ocean currents at the Darss and Drodgen Sills, and in the straits connecting the deep basins of the Baltic Sea.
  • Production and archiving of well-calibrated composite radar-based precipitation maps in near-real time from the existing international radar network in the Baltic Sea catchment region.
  • Two new weather radar installations at the eastern/south-eastern coast of the Baltic Sea.
  • Designated data centres to carry out the observational data storage functions.
  • Encourage field experiments and monitoring activities both in land and sea areas for a timely coordination with BRIDGE.

Modelling Requirements

  • Development of advanced coupled high-resolution atmosphere-hydrological-oceanographic models.
  • Two data assimilation centres to run independent delayed-mode data assimilation systems.
  • Intercomparison of model results, and comparison of the latter with observations, with special emphasis on surface processes.


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Last update of this page: 14 March 2007