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- Omstedt, Anders, 1949, et al.
(författare)
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Baltic Sea climate: 200 yr of data on air temperature, sea level variation, ice cover, and atmospheric circulation
- 2004
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Ingår i: Climate Research. - 0936-577X. ; 25:3, s. 205-216
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Tidskriftsartikel (refereegranskat)abstract
- Relevant observed time series for the Baltic Sea region from the last 2 centuries were used to investigate climate variations and trends. These time series were: Stockholm air temperature and magnitude of seasonal temperature cycle, Stockholm sea level data, Baltic Sea maximum ice cover, and circulation types based on regional air pressure data. The definition of climate was analysed by considering how each parameter varies with the time scale. We found that 90 % of the variance was for time scales shorter than 15 yr, the period then used as the climate-averaging time for all studied parameters. The results indicate positive trends for air temperature, sea level, and frequencies of anti-cyclonic circulation and westerly wind types over the last 200 yr. Negative trends were found for the magnitude of seasonal temperature cycle, sea-ice cover, and frequency of southwesterly wind. The major climate changes of the late 19 th century were probably associated with the end of the 'Little Ice Age' and characterized by an unusual high frequency of cyclonic circulation. In the 20 th century, pronounced positive trends were observed in sea level variation and anti-cyclonic circulation. In the most recent studied climate period (1985-2000), air temperature and sea level climate anomalies were positive and lay outside the range of last 200 yr normal variations. The study indicates that increased frequencies of anti-cyclonic circulation and westerly winds have resulted in a slightly warmer climate with reduced seasonal amplitude and reduced ice cover. Thereby, we support the hypothesis that the long-term climate change in the Baltic Sea region is at least partly related to changes in the atmospheric circulation.
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- Omstedt, Anders, 1949, et al.
(författare)
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Calculating the water and heat balances of the Baltic Sea using ocean modelling and available meteorological, hydrological and ocean data
- 2004
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Ingår i: Tellus Series a-Dynamic Meteorology and Oceanography. - : Stockholm University Press. - 0280-6495. ; 56:4, s. 400-414
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we aim to analyse Baltic Sea water and heat balances for the BALTEX/BRIDGE study period and to put these into a climatic perspective. The study period-the three years starting October 1999-was a time of enhanced observational and modelling activities in the Baltic Sea region and of the major field activity of BALTEX Phase I programme. The present study follows the example of earlier work, where Baltic Sea modelling was used as a tool for synthesizing available data and closing the water and heat balances. The modelling approach was validated with independent data sets of observations from salinity and temperature. The model simulation was also compared with the coupled atmosphere-Baltic Sea model system, HIRLAM-BALTEX, which was run in a delayed data assimilation mode. The results indicate that accurate long-term net water and net heat balances (mean errors over decadal time scales are about 600 m(3) s(-1) and 2 W m(-2) respectively) can be calculated using current Baltic Sea modelling and meteorological and hydrological data available from the BALTEX data centres. The accuracy of the individual terms in the water and heat balances is, however, still unknown. The study illustrated that negative net precipitation rates are possible, with the year 2002 standing out from the rest of the 30-yr study period. The calculated inter-annual variability of the net heat loss between atmosphere and Baltic Sea during the BALTEX/BRIDGE period indicated large variations ( 10 W m-2). It has also been shown that the Baltic Sea annual mean temperature has not increased during the studied period despite an atmospheric warming of I degreesC. The reason has been explained by the heat balance that indicated no trend in the Baltic Sea net heat loss.
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- Omstedt, Anders, 1949, et al.
(författare)
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Knowledge of the Baltic Sea physics gained during the BALTEX and related programmes
- 2004
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 63:1-2, s. 1-28
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Tidskriftsartikel (refereegranskat)abstract
- Review is given about the main results of the oceanographic component of the BALTEX research programme (one of the six continental scale experiments within GEWEX-WCRP to study water and energy cycles in the regional climate system) and related programmes/projects over the last 10 years. Working closely together with two other components regional meteorology and hydrology of the Baltic Sea drainage basin - oceanographic research has considerably improved the understanding of and ability to model the Baltic Sea marine system. In the Baltic Sea physics seven different broad topics are identified where knowledge has significantly improved. These are reviewed together with a discussion of gaps in knowledge. The focus is on the water and energy cycles of the Baltic Sea, but various aspects of forcing and validation data and modelling are also discussed. The major advances achieved through BALTEX and related programmes are: Meteorological, hydrological, ocean and ice data are now available for the research community. 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 introduced into Baltic Sea water and energy studies. Development of turbulence models and 3D ocean circulation models for application to the Baltic Sea. Improved Baltic Sea ice modelling and increased understanding of the need for coupled atmosphere-ice-ocean-land models. (C) 2004 Elsevier Ltd. All rights reserved.
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