首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 500 毫秒
1.
The mean sea level along the coasts of the Skagerrak, the Kattegat, and the Danish Straits—i.e., the transition area between the North Sea and the Baltic Sea—has been computed geodetically. The basis consists of mean sea level data from Denmark, Norway, and Sweden in various more or less inappropriate height systems. These are transformed and unified into a common height system relevant for oceanographic purposes to show the deviation of the mean sea level (1960) from the mean geoid, with Normaal Amsterdams Peil (NAP) as zero. The geodetically determined mean sea surface is compared with oceanographic model results for parts of the area. Among other findings, the outflow of low‐salinity water from the Baltic Sea, as well as its separation from high‐salinity North Sea water along the Kattegat‐Skagerrak front are clearly revealed.  相似文献   

2.
Editorial     
Karl Rinner 《Marine Geodesy》2013,36(3):203-205
The long‐term mean sea level in the Baltic Sea is investigated using the coupled three‐basin model constructed by Carlsson (1997). The model is forced by the observed sea level in the Kattegat, the freshwater supply, horizontal air pressure and density gradients, and the wind stress. Both the seasonal variations and the slope of the mean sea level are investigated and compared with the results of another oceanographic model (Lisitzin, 1962) and a geodetic model (Ekman &; Mäkinen, 1996). In the geodetic model an unofficial height system, NH60, is used, and one part of the investigation is to find out whether this height system is useful for oceanographers. The estimated mean sea level difference between the northern and the southern parts of the Baltic Sea are: 17.1 cm (the present model), 26 cm (Lisitzin's model), and 18.3 cm (the geodetic model). It is concluded that the mean sea level difference between the northern and southern parts of the Baltic Sea is due mainly to horizontal variations of density and air pressure, and that the height system NH60 is suitable for oceanographie applications.  相似文献   

3.
Long-term hourly data from 35 tide gauge stations, including 15 stations in the Gulf of Finland, were used to examine tidal sea level oscillations of the Baltic Sea. High-resolution spectral analysis revealed the well-defined fine structure of tidal peaks with diurnal peaks at most stations being higher than semidiurnal. At some stations (e.g., Narva, Daugava, and Wladyslawowo), high frequency radiational tidal peaks with periods multiple of the solar day (3, 4, 5, 6, and 8 cpd) were detected; the respective oscillations are supposed to be caused by seabreeze winds. Harmonic analysis of tides for individual yearly sea level series followed by vector averaging over the entire observational period was used to estimate the amplitudes and phases of 16 tidal constituents. The maximum tidal oscillations of 17–19 cm were found to be observed in the Gulf of Finland and, first of all, in Neva Bay (in the head of the gulf). Diurnal or mixed diurnal tides are predominant in almost the entire Baltic Sea. The comparison of the observed tides with those theoretically computed showed that the existing numerical models of the main tidal harmonics generally quite accurately reproduce the structure of the tides in the Baltic Sea except for some regions of the Gulf of Bothnia.  相似文献   

4.
The mean sea surface topography in the Baltic Sea and adjacent waters is reliably known in the Nordic height system NH 60. Using this knowledge we estimate differences between NH 60, based on the Amsterdam zero point, and Russian, Polish, and German height systems along the southeastern coast of the Baltic Sea, based on the Kronstadt zero point. The differences agree within a few centimeters. We also make a simple study of the mean sea level difference between Kronstadt and Amsterdam (which is found to have been approximately 25 cm when sea level was still to be seen there).  相似文献   

5.
Accessible high-quality observation datasets and proper modeling process are critically required to accurately predict sea level rise in coastal areas. This study focuses on developing and validating a combined least squares-neural network approach applicable to the short-term prediction of sea level variations in the Yellow Sea, where the periodic terms and linear trend of sea level change are fitted and extrapolated using the least squares model, while the prediction of the residual terms is performed by several different types of artificial neural networks. The input and output data used are the sea level anomalies (SLA) time series in the Yellow Sea from 1993 to 2016 derived from ERS-1/2, Topex/Poseidon, Jason-1/2, and Envisat satellite altimetry missions. Tests of different neural network architectures and learning algorithms are performed to assess their applicability for predicting the residuals of SLA time series. Different neural networks satisfactorily provide reliable results and the root mean square errors of the predictions from the proposed combined approach are less than 2?cm and correlation coefficients between the observed and predicted SLA are up to 0.87. Results prove the reliability of the combined least squares-neural network approach on the short-term prediction of sea level variability close to the coast.  相似文献   

6.
The pole tide, which is driven by the Chandler Wobble, has a period of about 14 months and typical amplitudes in the World Ocean of ～0.5 cm. However, in the Baltic Sea the pole tide is anomalously high. To examine this effect we used long-term hourly sea level records from 23 tide gauges and monthly records from 64 stations. The lengths of the series were up to 123 years for hourly records and 211 years for monthly records. High-resolution spectra revealed a cluster of neighboring peaks with periods from 410 to 440 days. The results of spectral analysis were applied to estimate the integral amplitudes of pole tides from all available tide gauges along the coast of the Baltic Sea. The height of the pole tide was found to gradually increase from the entrance (Danish Straits, 1.5–2 cm) to the northeast end of the sea. The largest amplitudes—up to 4.5–7 cm—were observed in the heads of the Gulf of Finland and the Gulf of Bothnia. Significant temporal fluctuations in amplitudes and periods of the pole tide were observed during the 19th and 20th centuries.  相似文献   

7.
使用ROMS(regional oceanic modeling system)模式模拟了40年的渤黄东海温盐流,数据包括三维的温度、盐度、流速、流向和海表高度,同时包含了逐小时的潮汐信息。将模拟结果与观测资料和卫星反演数据进行对比,检验了模式准确性。整体上,模式模拟的水位与近岸观测值基本一致,能够准确再现风产生的增水;模式较为准确的再现了渤黄东海的温度分布,在深水区模拟的温盐剖面与观测值基本一致;模式模拟渤黄东海区域的海表高度和海表流与卫星反演结果相比偏小,但分布趋势相近。模式结果可以为研究气候变化对水位的影响和黄海暖舌的扩散过程等现象提供数据支持。  相似文献   

8.
The dynamics controlling the response of the Baltic Sea to changed atmospheric and hydrologic forcing are reviewed and demonstrated using simple models. The response time for salt is 30 times longer than for heat in the Baltic Sea. In the course of a year, the Baltic Sea renews most of its heat but only about 3% of its salt. On the seasonal scale, surface temperature and ice-coverage are controlled by the atmospheric conditions over the Baltic Sea as demonstrated by e.g. the strong inter-annual variations in winter temperature and ice-coverage due to variations in dominating wind directions causing alternating mild and cold winters. The response of surface temperature and ice-coverage in the Baltic Sea to modest climate change may therefore be predicted using existing statistics. Due to the long response time in combination with complicated dynamics, the response of the salinity of the Baltic Sea cannot be predicted using existing statistics but has to be computed from mechanistic models. Salinity changes primarily through changes in the two major forcing factors: the supply of freshwater and the low-frequency sea level fluctuations in the Kattegat. The sensitivity of Baltic Sea salinity to changed freshwater supply is investigated using a simple mechanistic steady-state model that includes baroclinic geostrophic outflow from the Kattegat, the major dynamical factor controlling the freshwater content in the Kattegat and thereby the salinity of water flowing into the Baltic Sea. The computed sensitivity of Baltic Sea surface salinity to changes of freshwater supply is similar to earlier published estimates from time-dependent dynamical models with higher resolution. According to the model, the Baltic Sea would become fresh at a mean freshwater supply of about 60 000 m3 s−1, i.e. a 300% increase of the contemporary supply. If the freshwater supply in the different basins increased in proportion to the present-day supply, the Bothnian Bay would become fresh already at a freshwater supply of about 37 000 m3 s−1 and the Bothnian Sea at a supply of about 45 000 m3 s−1. The assumption of baroclinic geostrophic outflow from the Kattegat, crucial for the salinity response of the Baltic Sea to changed freshwater supply, is validated using daily salinity profiles for the period 1931–1977 from lightship Läsö Nord.  相似文献   

9.
东海沿海季节性海平面异常成因   总被引：1，自引：0，他引：1  
Based on the analysis of sea level, air temperature, sea surface temperature(SST), air pressure and wind data during 1980–2013, the causes of seasonal sea level anomalies in the coastal region of the East China Sea(ECS) are investigated. The research results show:(1) sea level along the coastal region of the ECS takes on strong seasonal variation. The annual range is 30–45 cm, larger in the north than in the south. From north to south, the phase of sea level changes from 140° to 231°, with a difference of nearly 3 months.(2) Monthly mean sea level(MSL)anomalies often occur from August to next February along the coast region of the ECS. The number of sea level anomalies is at most from January to February and from August to October, showing a growing trend in recent years.(3) Anomalous wind field is an important factor to affect the sea level variation in the coastal region of the ECS. Monthly MSL anomaly is closely related to wind field anomaly and air pressure field anomaly. Wind-driven current is essentially consistent with sea surface height. In August 2012, the sea surface heights at the coastal stations driven by wind field have contributed 50%–80% of MSL anomalies.(4) The annual variations for sea level,SST and air temperature along the coastal region of the ECS are mainly caused by solar radiation with a period of12 months. But the correlation coefficients of sea level anomalies with SST anomalies and air temperature anomalies are all less than 0.1.(5) Seasonal sea level variations contain the long-term trends and all kinds of periodic changes. Sea level oscillations vary in different seasons in the coastal region of the ECS. In winter and spring, the oscillation of 4–7 a related to El Ni?o is stronger and its amplitude exceeds 2 cm. In summer and autumn, the oscillations of 2–3 a and quasi 9 a are most significant, and their amplitudes also exceed 2 cm. The height of sea level is lifted up when the different oscillations superposed. On the other hand, the height of sea level is fallen down.  相似文献   

10.
This is a review of sea level data performed at three selected stations (Québec-Lauzon, Harrington Harbour,and Halifax) in eastern Canada in order to investigate the seasonal trends and other long-term and short-term changes which occurred since the beginning of the 20th century. Stations situated in riverine or estuarine regions (e.g., Québec-Lauzon) are significantly affected by freshwater flow in their annual cycle of sea level changes and exhibit a definite maximum in spring and minimum in autumn-winter. Other stations situated in the eastern half of the Gulf of St. Lawrence (e.g., Harrington Harbour) or near the open Atlantic coast (Halifax) mainly follow the general cycle of subarctic regions, with lows in spring-summer and highs in autumn-winter. Such seasonal variations appear to be related to the atmospheric pressure and baroclinic current variations. Secular trends in mean sea level in eastern Canadian waterbodies show a mean rise of about 2.56 mm/yr -1 due to tectonic motions, that is, land subsidence. At several stations in eastern Canada, evidence is found for the influence of the nodal tide (18.6 years), the sunspot cycle (10.8 years), the lunar perigee (8.47 years), the pole tide (14.5 months), the annual cycle (12 months), and semiannual tidal cycle (6 months) in sea level records. Beside long-term oscillations with periods of more than one year, evidence is found for high energetic semidiurnal and diurnal tides where they contribute largely (from 90-95%) to short term variability of sea level. In the residual signal (variations of sea level--tidal variations), short-term variations between 2 to 30 days can be attributed to meterological forcing (atmospheric pressure and winds), longitudinal seiches (2-10 h), atmospheric tides (12 h and 24 h) and inertial oscillations (16-18 h). A regressive model showed that the water discharge from the St. Lawrence River contributes 29% to the monthly residual sea level at Québec-Lauzon. The atmospheric pressure and winds contribute respectively 8.1% and 8.9% at this station. They contribute 52.1% and 7.7% at Harrington Harbour and 41.8% and 14.3% at Halifax. The regression coefficients of residual sea level on atmospheric pressure are respectively estimated to be -1.507 cm. ( hPa ) -1 ( - 0.345 cm. ( hPa ) -1 ), -0.776 cm. ( hPa ) -1 ( - 0.112 cm. ( hPa ) -1 ) and -0.825 cm. ( hPa ) -1 ( - 0.008 cm. ( hPa ) -1 ) at the three stations. Compared to the coefficient of the inverted barometer, estimated to be -1 cm. ( hPa ) -1 , these effects of the atmospheric pressure on sea level variations seem to be amplified at Que´bec-Lauzon by the wind effects (and water discharge) while they are reduced at Harrington Harbour and Halifax.  相似文献   

11.
The sensitivity of the Baltic Sea mean salinity to climatic changes of the freshwater supply is analyzed. The average salinity of the Baltic Sea is about 6‰. The low salinity is an effect of a large net freshwater supply and narrow and shallow connections with the North Sea. As a result of mixing in the entrance area, a large portion of the outflowing Baltic Sea water returns with the inflowing salty water and thus lowers the salinity of the Baltic Sea deep-water considerably. This recycling of the Baltic Sea water is a key process determining the salinity of today's Baltic Sea. The sensitivity of this recycling, and thus of the Baltic Sea salinity, to climatic changes in the freshwater supply is analyzed. A simple model is formulated for the variations of the Baltic Sea freshwater content. Historical data of the freshwater supply and the salinity in the Baltic Sea are used in the model to achieve an empirical expression relating variations of the recycling of Baltic Sea water to the variations of the freshwater supply. The recycling is found to be very sensitive to the freshwater supply. We find that an increase of freshwater supply of 30% is the level above which the Baltic Sea would turn into a lake. Recent climate modeling results suggest that river runoff to the Baltic Sea may increase dramatically in the future and thus possibly put the Baltic Sea into a new state.  相似文献   

12.
1 .IntroductionTheglobalairtemperatureroseabout 0 .5～ 0 .6°Coverthepast 2 0thcentury ,andtheglobalmeansealevelincreasedbyabout2 0cmduringtheperiod .Theregionalmeansealevelriseswiththerisingglobalmeansealevel.Zuoetal.( 1 997)indicatedthatthemeanrisingrateofabsolutemeansealevelalongtheChinacoastontheassumptionofunifiedisostaticdatumis 2mm a .Woodworth( 1 999)analyzedsealevelspanning 1 76 8tothepresentinLiverpool,andobtainedaseculartrendforheperiodupto 1 880of0 .39± 0 .1 7mm a ,andatrendfort…  相似文献   

13.
Statistical analysis of the extreme values of the Baltic Sea level has been performed for a series of observations for 15–125 years at 13 tide gauge stations. It is shown that the empirical relation between value of extreme sea level rises or ebbs (caused by storm events) and its return period in the Baltic Sea can be well approximated by the Gumbel probability distribution. The maximum values of extreme floods/ebbs of the 100-year recurrence were observed in the Gulf of Finland and the Gulf of Riga. The two longest data series, observed in Stockholm and Vyborg over 125 years, have shown a significant deviation from the Gumbel distribution for the rarest events. Statistical analysis of the hourly sea level data series reveals some asymmetry in the variability of the Baltic Sea level. The probability of rises proved higher than that of ebbs. As for the magnitude of the 100-year recurrence surge, it considerably exceeded the magnitude of ebbs almost everywhere. This asymmetry effect can be attributed to the influence of low atmospheric pressure during storms. A statistical study of extreme values has also been applied to sea level series for Narva over the period of 1994–2000, which were simulated by the ROMS numerical model. Comparisons of the “simulated” and “observed” extreme sea level distributions show that the model reproduces quite satisfactorily extreme floods of “moderate” magnitude; however, it underestimates sea level changes for the most powerful storm surges.  相似文献   

14.
An analysis of the variations in the concentrations of 137Cs and 90Sr radionuclides in the Baltic Sea surface waters after the accident at the Chernobyl nuclear power plant was performed. An instability of the 137Cs concentration values during the short-term observations was found, when these values were differed 2-to 3-fold. The concentrations of 90Sr appeared to be more stable; meanwhile, their deviations sometimes exceeded the ranges of the experimental errors. By the variations in the monthly average values of the radionuclide concentrations in the surface waters of the Baltic Sea in 1989–1995, no trend of the water self-purification was observed. The theoretical results obtained confirmed the potential of the formation and propagation of patches with increased concentrations of 137Cs in the southeastern part of the Baltic Sea. The most reliable factor that controlled the process of self-purification of the Baltic Sea water appeared to be the mean annual value of the concentration of radionuclides. Pronounced divergences were obtained between the measured and calculated mean annual concentrations of 137Cs and 90Sr radionuclides in the surface waters of the Baltic Sea in 1989–2001. These divergences are explained by the potential influence of the waters from the Gulf of Bothnia and by other additional supplies of radionuclides to the marine environment, which were not included into the mathematical models.  相似文献   

15.
Abstract

We studied geoid validation using ship-borne global navigation satellite systems (GNSS) on the Baltic Sea. We obtained geoid heights by combining GNSS–inertial measurement unit observations, tide gauge data, and a physical sea model. We used two different geoid models available for the area. The ship route was divided into lines and the lines were processed separately. The GNSS results were reduced to the sea surface using attitude and draft parameters available from the vessel during the campaign. For these lines, the residual errors between ellipsoidal height versus geoid height and absolute dynamic topography varied between 0 and 15?cm, grand mean being 2?cm. The mean standard deviations of the original time series were approximately 11?cm and reduced to below 5?cm for the time series filtered with 10?min moving average. We showed that it is possible to recover geoid heights from the GNSS observations at sea and validate existing geoid models in a well-controlled area.  相似文献   

16.
The Baltic Sea Level Project is an international scientific observation program to unify the vertical datums of the countries of the Baltic Sea with GPS measurements. In total, 35 tide gauges on shores and islands of the Baltic were occupied with GPS in 1993. After computing a new gravimetric geoid over the Baltic Sea, it was possible to unify the datums as well as to calculate the orthometric heights and the sea surface topography values for the tide gauge stations. The results obtained are shown.  相似文献   

17.
The connection between variations in the North Atlantic Oscillation (NAO) index and the Baltic sea level has been investigated for the period 1825–1997. The association between the NAO and the strength of the zonal geostrophic wind stress over the Northwest Atlantic suggests an NAO impact on Baltic sea level variations, because the monthly mean sea level mainly is determined by externally driven variations caused by wind conditions over the North Sea. Several period bands were found to have high correlation between oscillations in the winter (JFM) NAO index and the Baltic Sea winter mean sea level. The correlation was, however, higher in the 20th century than in the 19th. During the last two decades, the correlation between the NAO index and the sea level has been exceptionally high. The winter mean of a regional atmospheric circulation index had a correlation with the Kattegat winter mean sea level of 0.93. With the Baltic sea level the correlation was 0.91, compared with the NAO index correlation for the same period of 0.74. The regional index also showed a high correlation with the mean summer and mean autumn sea levels, when the corresponding seasonal NAO indices showed a weak connection. The temporal variation of the connection with the NAO index implies a regional atmospheric circulation occasionally differing from the large-scale circulation associated with the NAO. Seasonal means of the sea level in Stockholm do, however, reflect the regional wind climate to a large extent, and the Baltic sea level is a useful proxy for identifications of climatic dependencies in the region.  相似文献   

18.
Variability of Sea Surface Circulation in the Japan Sea   总被引：3，自引：0，他引：3  
Composite sea surface dynamic heights (CSSDH) are calculated from both sea surface dynamic heights that are derived from altimetric data of ERS-2 and mean sea surface that is calculated by a numerical model. The CSSDH are consistent with sea surface temperature obtained by satellite and observed water temperature. Assuming the geostrophic balance, sea surface current velocities are calculated. It is found that temporal and spatial variations of sea surface circulation are considerably strong. In order to examine the characteristics of temporal and spatial variation of current pattern, EOF analysis is carried out with use of the CSSDH for 3.5 years. The spatial and temporal variations of mode 1 indicate the strength or weakness of sea surface circulation over the entire Japan Sea associated with seasonal variation of volume transport through the Tsushima Strait. The spatial and temporal variations of mode 2 mostly indicate the temporal variation of the second branch of the Tsushima Warm Current and the East Korean Warm Current. It is suggested that this variation is possibly associated with the seasonal variation of volume transport through the west channel of the Tsushima Strait. Variations of mode 3 indicate the interannual variability in the Yamato Basin.  相似文献   

19.
As part of the Vertical Offshore Reference Frames (VORF) project sponsored by the U. K. Hydrographic Office, a new model for Sea Surface Topography (SST) around the British Isles has been developed. For offshore areas (greater than 30 km from the coast), this model is largely derived from satellite altimetry. However, its accuracy and level of detail have been enhanced in coastal areas by the inclusion of not only the 60 PSMSL tide gauges with long-term records around the coasts of the United Kingdom and Ireland but also some 385 gauges established at different epochs and for different observation spans by the U. K. Admiralty. All tide gauge data were brought into a common reference frame by a combination of datum models and direct GPS observations, but a more significant challenge was to bring all short-term sea level observations to an unbiased value at a common epoch. This was achieved through developing a spatial-temporal correlation model for the variations in mean sea level around the British Isles, which in turn meant that gauges with long-term observation spans could be used as control points to improve the accuracy of Admiralty gauges. It is demonstrated that the latter can contribute point observations of mean sea level (MSL) with a precision of 0.078 m. A combination of least squares collocation and interpolation was developed to merge the coastal point and offshore gridded data sets, with particular algorithms having to be developed for different configurations of coastal topology. The resulting model of sea surface topography is shown to present a smooth transition from inshore coastal areas to offshore zones. Further benefits of the techniques developed include an enhanced methodology for detecting datum discontinuities at permanent tide gauges.  相似文献   

20.
With improved observation methods, increased winter navigation, and increased awareness of the climate and environmental changes, research on the Baltic Sea ice conditions has become increasingly active. Sea ice has been recognized as a sensitive indicator for changes in climate. Although the inter-annual variability in the ice conditions is large, a change towards milder ice winters has been detected from the time series of the maximum annual extent of sea ice and the length of the ice season. On the basis of the ice extent, the shift towards a warmer climate took place in the latter half of the 19th century. On the other hand, data on the ice thickness, which are mostly limited to the land-fast ice zone, basically do not show clear trends during the 20th century, except that during the last 20 years the thickness of land-fast ice has decreased. Due to difficulties in measuring the pack-ice thickness, the total mass of sea ice in the Baltic Sea is, however, still poorly known. The ice extent and length of the ice season depend on the indices of the Arctic Oscillation and North Atlantic Oscillation. Sea ice dynamics, thermodynamics, structure, and properties strongly interact with each other, as well as with the atmosphere and the sea. The surface conditions over the ice-covered Baltic Sea show high spatial variability, which cannot be described by two surface types (such as ice and open water) only. The variability is strongly reflected to the radiative and turbulent surface fluxes. The Baltic Sea has served as a testbed for several developments in the theory of sea ice dynamics. Experiences with advanced models have increased our understanding on sea ice dynamics, which depends on the ice thickness distribution, and in turn redistributes the ice thickness. During the latest decade, advance has been made in studies on sea ice structure, surface albedo, penetration of solar radiation, sub-surface melting, and formation of superimposed ice and snow ice. A high vertical resolution has been found as a prerequisite to successfully model thermodynamic processes during the spring melt period. A few observations have demonstrated how the river discharge and ice melt affect the stratification of the oceanic boundary layer below the ice and the oceanic heat flux to the ice bottom. In general, process studies on ice–ocean interaction have been rare. In the future, increasingly multidisciplinary studies are needed with close links between sea ice physics, geochemistry and biology.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号