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BALTEX - The Baltic Sea experiment

Summary information

Funding:Project in the framework of the Regional Hydroclimate Project (RHP) of the Coordinated Energy and Water Cycle Observations Project (CEOP) within the Global Energy and Water Cycle Experiment (GEWEX) of the World Climate Research Programme (WCRP). Since January 2002, GKSS (now Helmholtz-Zentrum Geesthacht, HZG) has been the only sponsor of the International BALTEX Secretariat (IBS), covering salaries for the IBS staff members, infrastructure and travel support.
Start date:1993-01-01
End date:2012-01-01
Duration: months
Coordinator:Helmholtz-Zentrum Geesthacht – Germany
Project name:BALTEX - The Baltic Sea experiment
Project summary:Abstract
BALTEX (the Baltic Sea Experiment) is a Regional Hydroclimate Project (RHP) of the Coordinated Energy and Water Cycle Observations Project (CEOP) within the Global Energy and Water Cycle Experiment (GEWEX) of the World Climate Research Programme (WCRP).

The research focus of BALTEX Phase I (1993-2002) was primarily on the hydrological cycle and the exchange of energy between the atmosphere and the surface of the Earth, as they control and regulate the climate in a fundamental manner. BALTEX Phase II (2003-2012) has extended the scope of research to regional climate change, water management and biogeochemical cycles and transport processes in the regional Earth system. The study region of BALTEX is the Baltic Sea and its hydrological drainage basin, which constitutes a unique European water basin, creating specific demands on models and scientific concepts

The numerous scientific achievements of BALTEX Phase I have called for application in other areas where knowledge on and modelling capabilities of the water and energy cycles in the climate system are fundamental. A Science Plan for BALTEX Phase II has therefore been published in early 2004, which defines 6 major objectives including several specific goals with the overall strategy to enlarge the scientific scope of the programme and also to contribute to generating environmental policy- and stakeholder relevant information.

An important aspect of BALTEX Phase II will be a more holistic approach towards observing, understanding and modelling major environmental and socio-economic aspects relevant for the entire Baltic Sea basin. Parts of the BALTEX Phase II research activities will thus contribute to the build-up of a high resolution integrated modelling capability for Northern Europe, embedded in an Earth System Model.


BALTEX Phase I Objectives, formulated in 1995:
• To explore and model the various mechanisms determining the space and time variability of energy and water budgets of the BALTEX region and this region’s interactions with surrounding regions
• To relate these mechanisms to the large-scale circulation systems in the atmosphere and oceans over the globe
• To develop transportable methodologies in order to contribute to basic needs of climate, climate impact, and environmental research

BALTEX comprises both meteorological and hydrological research. Additionally, it has a strong oceanographic research component, at present a unique feature among the GEWEX regional-scale projects. BALTEX is designed as a cage experiment to assess the total heat and water flux divergence of the BALTEX area. The basic BALTEX programme elements include numerical modelling, data assimilation, experimental and numerical process studies, re-analysis of existing data sets, and application of remote sensing.

BALTEX Phase II (2003-2012) exceeds the scope of BALTEX to more applied and environmental research areas such as:
• Climate change and extreme events
• Improving tools for water management
• Air and water quality
• Involvement of stakeholders and decision makers
• Education and outreach

Basic research in the field of water and energy cycles remains the backbone of the programme. The vision is to create a common platform for scientists from all environmental disciplines, striving towards an integrative description of the Baltic Sea basin, including a retrospective modelling of the past and the simulation of the Baltic Sea basin environment in the future. An important aspect of BALTEX Phase II is the holistic approach towards observing, understanding and modelling major environmental and socio-economic aspects relevant for the entire Baltic Sea basin. BALTEX Phase II research thus contributes to the build-up of a high resolution integrated modelling capability for Northern Europe, embedded in an Earth System Model.
Project outputs:Achievements of BALTEX Phase I
BALTEX Phase I has generated active research covering the whole field of advanced modelling and data studies in meteorology, hydrology and oceanography. Major research elements of BALTEX include the collection of in situ and remote sensing data, re-analysis of existing data sets, data assimilation, numerical experiments and coupled modelling and process studies including field experiments. It has brought major results both in scientific knowledge and research infrastructure at the European level.
In the following, a short overview over major achievements of BALTEX Phase I is given for the major compartments of the water and energy cycle of the Baltic Sea basin:

Phase I Achievements: Atmosphere
• Improved understanding of sea-atmosphere and land-atmosphere interaction in the BALTEX region through observational studies and offline model evaluation and through numerical studies with coupled models.
• Improved knowledge on precipitation and evaporation over the BALTEX region through new instruments, radar estimates and satellite sensors.
• Development of improved remote sensing techniques to determine e.g. precipitation rates by weather radar, precipitable water by GPS and cloud climatologies by AVHRR.
• Improvement of understanding and modelling of cloud physics, cloud-radiation interaction and precipitation initiation.
• Development of retrieval methods for cloud liquid water path from passive imagers and optimized estimates of the spatial distribution of liquid cloud water.
• Assessment of model liquid water path, cloud vertical structure and cloud overlap with microwave, lidar and cloud radar observations and the impact on radiation.
• Development of fully coupled atmosphere-land-ocean models of the Baltic Sea basin for present day and climate change applications.

Examples include the first coupled regional models for the entire Baltic Sea basin and improved water budget estimates through newly assimilated data sets. Also special observing periods, such as the Pilot Study for Intensive Data Collection and Analysis of Precipitation (PIDCAP) in 1995, and BRIDGE, the major enhanced observational period within BALTEX during 1999 to 2002 with dedicated additional observations, were conducted in the frame of BALTEX. BALTEX projects are still ongoing in different countries funded mainly by institutional and national sources.
Phase I Achievements: Hydrology and Runoff
• A database of monthly river flow has been compiled and made available through the BALTEX Hydrological Data Centre.
• Large-scale hydrological models of river flow to the Baltic Sea exist.
• Improved communication between meteorologists and hydrologists resulting in a better understanding of the water cycle and the modelling of it.
• Lateral water transport through runoff routing has been applied in climate models.
• Efforts to improve flood forecasting schemes with the help of regional atmospheric models for specific river basins have been made.
• Climate change scenarios of impacts to the water cycle in the Baltic Sea basin have been performed.

BALTEX Phase I has marked a significant advance in research on regional meteorology, hydrology of the Baltic Sea basin as well as oceanography of the Baltic Sea including sea ice. Results of BALTEX are documented in more than 250 peer-reviewed journal articles and numerous reports. Special journal volumes dedicated to the four BALTEX Study Conferences held in 1995, 1998, 2001 and 2004 provide comprehensive insight to BALTEX results. These include issues of Tellus (1996, Volume 48 A, No 5), Meteorologische Zeitschrift (2000, Volume 9, No 1 and 2), Meteorological and Atmospheric Physics (2001, Volume 77, No 1-4), Boreal Environmental Research (2002, Volume 7, No 3 and 4), and Nordic Hydrology (2005, Volume 36, Issues 4-5). Achievements of BALTEX Phase I have been compiled in a detailed state-of-the-art report (BALTEX, 2005). For a comprehensive overview over BALTEX publications, click here.
Phase I Achievements: Baltic Sea including sea-ice
- Meteorological, hydrological, ocean and ice data are now available for the research community through BALTEX data centres.
- Progress in understanding of the strong impact of large-scale atmospheric circulation on Baltic Sea circulation, water mass exchange, sea ice evolution, and changes in the ocean conditions of the Baltic Sea.
- Progress in understanding of the importance of strait flows in the exchange of water into and within the Baltic Sea.
- Progress in understanding of intra-basin processes.
- Ocean models are introduced to Baltic Sea water and energy studies.
- Development of turbulence models and 3D ocean circulation models for Baltic Sea.
- Advances of thermodynamic and dynamic coupling between the atmosphere, sea ice, and the sea; field experiments and modelling studies have yielded new results on local and regional surface fluxes and the interaction of the atmospheric boundary layer, sea ice, and open water.
- Progress in understanding the interaction between sea ice dynamics and thermodynamics.
- Advanced understanding of effects of river discharge and ice melt on the oceanic boundary layer below sea ice.
- Advanced understanding of the role of the large-scale atmospheric circulation for the ice conditions in the Baltic Sea.