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1.
The influence of climate changes in Eurasia on the Caspian Sea level fluctuations in the Holocene is studied on the basis of historical data. The correspondence of the Late Khvalyn transgression to the time of the thawing of the European (Scandinavian) ice cap is revealed as well as that of the climatic optimum of the Holocene to the Boreal period (10-8 thousand years ago). In the next New-Caspian epoch, the Caspian Sea regression occurred. In the historical time, the maxima of cold snaps and Caspian Sea level are registered every five centuries.  相似文献   

2.
The variability ofthe level and area ofthe Caspian Sea during the Late Glacial Maximum and Holocene is analyzed. It is found that sea level variations during the period of quasisteady Holocene climate can be represented as a result of the accumulation of small anomalies in the water regime, i.e., as a manifestation of the self-developing system. The model of the Caspian Sea water balance was used to test this hypothesis. Empirical data on various-scale sea level variations are presented, and an attempt to explain their nature is made. The origin of large transgressions and regressions is analyzed.  相似文献   

3.
The Caspian Sea is the largest enclosed body of water on earth, covering approximately 4×105 km2 and sharing its coast with five countries (Iran, Azerbaijan, Kazakhstan, Russia and Turkmenistan). Because it has no outlet to the ocean the Caspian Sea level (CSL) has undergone rapid shifts in response to climatic forcings, and these have been devastating for the surrounding countries. In this paper we present the initial results of a modeling effort aimed at building a regional climate model for the Caspian Sea basin suitable to study the response of the CSL to interdecadal climate variability and anthropogenic climate change. Simulations are performed using the International Centre for Theoretical Physics (ICTP) regional climate model RegCM at a 50 km grid spacing for the period 1948–1990. During this period an abrupt shift occurred in the sea level after 1977, when the CSL rose about two meters until the early 1990s. Using a simple equation of hydrologic balance for the Caspian Sea basin to predict the CSL, we show that the model is able to reproduce the observed CSL changes at interannual to multidecadal scales. The correlation coefficient between the simulated and observed annual CSL changes is 0.91 and the model is able to reproduce the abrupt shift in CSL which occurred after 1977. Analysis of the climatologies before and after 1977 indicate that the CSL rise was mostly due to an increase in precipitation over the northern basin and a decrease in evaporation over the sea, primarily during the warm season. We plan to apply our model to the investigation of the response of the CSL to anthropogenic climate forcings.  相似文献   

4.
The characteristics of storm surges obtained from sea level observations at four hydrometeorological stations in the North Caspian Sea for 2003–2017 are presented. The sea level that by 30 cm exceeds the monthly mean value at the analyzed point of the Caspian Sea was considered as a surge. In total, 370 surges were registered, 83% of them occurred during the cold season (September-April). The maximum surge height was 125 cm, the longest duration was 7 days. The most significant surges on Tyulenii Island were simulated with the operational hydrodynamic model of the sea level and currents of the Caspian Sea using atmospheric forcing from the COSMO model. The mean coefficient of correlation between the simulated and observed sea level is equal to 0.94.  相似文献   

5.
The paleo-evolution of the Black Sea level during the Lateglacial–Holocene transition is still unclear, which motivates us to provide new estimates for that period based on the analysis of water budget. Hydrological conditions in the Black Sea catchment area are reconstructed here using water balance equation, available data, and constraints based on simple theory relating the runoff ratio with climatic characteristics. In order to estimate the impact of the aridity of climate we consider two alternative scenarios: (1) climate change under constant in time gradient in precipitation and evaporation over land and sea, and (2) climate change accounting for changes in the horizontal distribution of precipitation and evaporation. Hydrological data are compiled from available present-day data and paleo-observations. A number of sensitivity experiments is carried out revealing that the hydrological conditions in the Black Sea watershed should have evolved towards a very arid climate (similar to the present-day climate in the Caspian Sea area) in order to initiate a drop of sea level of ∼100 m below the sill depth of the Bosporus Straits, as speculated in some recent research. Estimates of sea level changes reveal a qualitative agreement with the coast-line evolution inferred from paleo-observations. The Younger Dryas draw down of the Black Sea starts at about 13.3 to 13 kyr BP, with a maximum low-stand of 104 m at 11.5 kyr BP. In an arid climate scenario the sea level reaches the outlet at about 8.8 to 7.4 kyr BP. Approximately at that time, Mediterranean sea level was about 10 m higher, making flooding events of the Black Sea possible. However, the nature and exact timing of the Holocene reconnection depends also on other (not well known) factors; one of them is the Bosporus sill depth, motivating further research in this field. Estimates of the water transport through the Bosporus Straits are also provided for the time of Lateglacial–Holocene transition.  相似文献   

6.
Probable climate changes in Russia in the 21st century are considered based on the results of global climate simulations with an ensemble of coupled atmosphere-ocean CMIP3 models. The future changes in the surface air temperature, atmospheric pressure, cloud amount, atmospheric precipitation, snow cover, soil water content, and annual runoff in Russia and some of its regions in the early, middle, and late 21st century are analyzed using the A2 scenario of the greenhouse gas and aerosol emission. Future changes in the yearly highest and lowest surface air temperatures and in summer precipitation of high intensity are estimated for Russia. Possible oscillations of the Caspian Sea level associated with the expected global climate warming are estimated. In addition to the estimates of the ensemble mean changes in climatic characteristics, the information about standard deviations and statistical significance of the corresponding climate changes is given.  相似文献   

7.
Jiongxin Xu 《Climatic change》2012,112(2):283-298
Controlled by continental monsoon climate, runoff of the Yellow River shows large temporal variability. How runoff responds to the changing summer monsoon intensity is important both in theory and in water resources management. The earliest hydrological observations on the Yellow River started in 1919, and thus, runoff data are available only for the past 90 years. Using data of the summer monsoon intensity (SMI), the temporal variation of SMI since 1873 and the resultant variation in runoff are dealt with for the drainage area between Hekouzhen and Longmen, Yellow River basin. At the 128-year scale, the variation of SMI can be generalized as a trend of decreasing first, then increasing and then decreasing again. At the time scale of 50 years for which concurrent data are available, the temporal variations in both SMI and precipitation show some decreasing trend. At the time scale of 80 years for which concurrent data were available, the temporal variations in SMI and natural runoff also show a decreasing trend. For 5-year moving averages of these variables, the synchronous trend of variation is more obvious. This fact indicates that the variation in SMI results in the variations in precipitation and runoff in the study area. Based on data of SMI and natural runoff for the period from 1920 to 2000, a regression equation between the 5-year moving averages of SMI (SMI5m) and natural runoff (Q wn,5m) was established, which shows that 72% of the variation in Q wn,5m can be explained by the variation in SMI5m. Using this regression equation, Q wn,5m for the period from 1873 to 1919 was reconstructed. At the 128-year scale, the natural runoff from the study area shows a trend of decreasing first, then increasing and then decreasing again, in response to the similar variation in the summer monsoon intensity.  相似文献   

8.
A high-precision digital elevation model of the Caspian Sea with the spatial resolution of 0.001° x 0.001° is constructed and used as a basis for computation grids of various scales. A three-level scheme for calculating wind waves with the sequence of nested grids (Caspian Sea-Northern Caspian, Absheron Peninsula, Turkmenbashy city-the Northern Caspian key areas) is developed. A scenario designer is implemented which considers in calculations the ice edge position and the coastline dynamics. The SWAN spectral wave model is adapted to the Caspian Sea conditions. The series of calculations and the comparison of the obtained results with observational data are provided. It is found that the best result is obtained when corrected reanalysis data are used for calculations.  相似文献   

9.
The observational data on sea level at Tyulenii Island station were compared with the results of the Caspian Sea level simulation with the three-dimensional hydrodynamic model with different spatial horizontal resolution (3 and 1 nautical miles). The sea motion is induced by the air pressure gradients and tangential wind stress that are obtained from the COSMO model forecast and specified on the surface. The results of diagnostic calculations of the sea level for June-October 2014 and 60 forecasts for September 2014 demonstrated that the model with the 1-mile resolution meets the simulation accuracy requirements of the Hydrometcenter of Russia and can be used for the short-range forecasting of the Caspain Sea level.  相似文献   

10.
The Caspian Sea level and flow velocity are calculated with a three-dimensional baroclinic model with free surface using the reanalysis data on meteorological variables for 1948–2004. The results are compared with the data on the sea level observations at the coastal stations. It is shown that the model adequately reproduces intraannual changes of the sea level. For effective computations with multiprocessor computers, a parallel model version is developed, which has a significant advantage of the usual version in the computation speed.  相似文献   

11.
The main components ofthe Caspian Sea water balance and water level are assessed. Stochastic models of time series of the water balance components are proposed ustng morphometric dependences specified by creating and processing digital elevation models for the flooded areas. The sea level forecast is obtained by the method of simulation modeling based on algorithms for the generation of Markovian random sequences with non-Gaussian marginal distributions.  相似文献   

12.
A regional ocean circulation model was used to project Baltic Sea climate at the end of the twenty-first century. A set of four scenario simulations was performed utilizing two global models and two forcing scenarios. To reduce model biases and to spin up future salinity the so-called Δ-change approach was applied. Using a regional coupled atmosphere–ocean model 30-year climatological monthly mean changes of atmospheric surface data and river discharge into the Baltic Sea were calculated from previously conducted time slice experiments. These changes were added to reconstructed atmospheric surface fields and runoff for the period 1903–1998. The total freshwater supply (runoff and net precipitation) is projected to increase between 0 and 21%. Due to increased westerlies in winter the annual mean wind speed will be between 2 and 13% larger compared to present climate. Both changes will cause a reduction of the average salinity of the Baltic Sea between 8 and 50%. Although salinity in the entire Baltic might be significantly lower at the end of the twenty-first century, deep water ventilation will very likely only slightly change. The largest change is projected for the secondary maximum of sea water age within the halocline. Further, the average temperature will increase between 1.9 and 3.2°C. The temperature response to atmospheric changes lags several months. Future annual maximum sea ice extent will decrease between 46 and 77% in accordance to earlier studies. However, in contrast to earlier results in the warmest scenario simulation one ice-free winter out of 96 seasons was found. Although wind speed changes are uniform, extreme sea levels may increase more than the mean sea level. In two out of four projections significant changes of 100-year surge heights were found.  相似文献   

13.
Weather patterns of the cold season in the studied region of the Caspian Sea are quite complicated; ice processes here represent an actual threat for hydrotechnical and other engineering constructions located both on the coast and the Northern Caspian Sea shelf, as well as for the navigation in the ice covered sea. Analysis of the materials obtained from the researches performed in November 2007–March 2008 showed that weather patterns of the 2007–2008 cold season in the Northern Caspian Sea formed under the influence of synoptic processes differed from the multiyear norm. The unusually high frequency of anticyclonic processes (especially, the Siberian anticyclone) defined the low monthly average air temperature in January that was 2–5°C below the climatologic norm over the entire Northern Caspian water area.  相似文献   

14.
基于气象和水文观测资料,分析白河流域年径流量与气象要素的关系并建立拟合模型,利用CMIP5模式在不同典型浓度路径(RCPs)下的模拟结果,预估21世纪白河流域年径流量的变化特征.结果表明:1981～2012年白河流域年径流量呈先减少后增加的变化趋势,与气象站观测的年平均最高气温呈显著负相关,与降水量呈显著正相关.以红原...  相似文献   

15.
A data-model intercomparison study of Arctic sea-ice variability   总被引：1，自引：0，他引：1  
Armstrong  A.  Tremblay  L.-B.  Mysak  L. 《Climate Dynamics》2003,20(5):465-476
The dynamic-thermodynamic granular rheology sea-ice model of Tremblay and Mysak is validated against 40 years of observed sea-ice concentration (SIC) data. Subsequently, the mechanisms responsible for producing SIC anomalies in the model are evaluated by studying the coupled variance (using the singular value decomposition method, SVD) between the simulated SIC anomalies and the ice speed and air temperature anomalies. To execute this validation, a 49-year (1949-97) simulation (including a 9-year spin-up period) of the Arctic and peripheral sea-ice cover using daily varying winds and monthly mean air temperatures is produced. In general, the simulated SIC variations for 1958-97 in the East Siberian, Chukchi and Beaufort seas are in agreement with observations, while larger discrepancies occur in the Laptev and Kara seas. Moreover, the sensitivity of the model to southerly wind anomalies in creating summer SIC anomalies compares well with the observed sensitivity; however, the model's sensitivity to summer air temperature anomalies is weaker than observed. The summer SIC anomalies over an entire sea are not influenced by variations in the level of river runoff. Results from the SVD analysis show that the main source of variability in the peripheral seas is associated with the variation in the strength of the Arctic High; in the East Siberian and Laptev seas, the strengthening and weakening of the Transpolar Drift Stream also play an important role. Over the entire Arctic domain, surface air temperature anomalies are negatively correlated with sea-ice anomalies. Finally, the observed downward trend in total sea-ice cover in the last two decades as well as record minima in the East Siberian Sea are well reproduced in the simulation.  相似文献   

16.
Atmosphere–ocean interactions are known to dominate seasonal to decadal sea level variability in the southeastern North Sea. In this study an atmospheric proxy for the observed sea level variability in the German Bight is introduced. Monthly mean sea level (MSL) time series from 13 tide gauges located in the German Bight and one virtual station record are evaluated in comparison to sea level pressure fields over the North Atlantic and Europe. A quasi-linear relationship between MSL in the German Bight and sea level pressure over Scandinavia and the Iberian Peninsula is found. This relationship is used (1) to evaluate the atmospheric contribution to MSL variability in hindcast experiments over the period from 1871–2008 with data from the twentieth century reanalysis v2 (20CRv2), (2) to isolate the high frequency meteorological variability of MSL from longer-term changes, (3) to derive ensemble projections of the atmospheric contribution to MSL until 2100 with eight different coupled global atmosphere–ocean models (AOGCM’s) under the A1B emission scenario and (4) two additional projections for one AOGCM (ECHAM5/MPI-OM) under the B1 and A2 emission scenarios. The hindcast produces a reasonable good reconstruction explaining approximately 80 % of the observed MSL variability over the period from 1871 to 2008. Observational features such as the divergent seasonal trend development in the second half of the twentieth century, i.e. larger trends from January to March compared to the rest of the year, and regional variations along the German North Sea coastline in trends and variability are well described. For the period from 1961 to 1990 the Kolmogorov-Smirnow test is used to evaluate the ability of the eight AOGCMs to reproduce the observed statistical properties of MSL variations. All models are able to reproduce the statistical distribution of atmospheric MSL. For the target year 2100 the models point to a slight increase in the atmospheric component of MSL with generally larger changes during winter months (October–March). Largest MSL changes in the order of ~5–6 cm are found for the high emission scenario A2, whereas the moderate B1 and intermediate A1B scenarios lead to moderate changes in the order of ~3 cm. All models point to an increasing atmospheric contribution to MSL in the German Bight, but the uncertainties are considerable, i.e. model and scenario uncertainties are in the same order of magnitude.  相似文献   

17.
Marine proxy evidence linking decadal North Pacific and Atlantic climate   总被引：1，自引：1，他引：0  
Decadal- to multidecadal variability in the extra-tropical North Pacific is evident in 20th century instrumental records and has significant impacts on Northern Hemisphere climate and marine ecosystems. Several studies have discussed a potential linkage between North Pacific and Atlantic climate on various time scales. On decadal time scales no relationship could be confirmed, potentially due to sparse instrumental observations before 1950. Proxy data are limited and no multi-centennial high-resolution marine geochemical proxy records are available from the subarctic North Pacific. Here we present an annually-resolved record (1818–1967) of Mg/Ca variations from a North Pacific/Bering Sea coralline alga that extends our knowledge in this region beyond available data. It shows for the first time a statistically significant link between decadal fluctuations in sea-level pressure in the North Pacific and North Atlantic. The record is a lagged proxy for decadal-scale variations of the Aleutian Low. It is significantly related to regional sea surface temperature and the North Atlantic Oscillation (NAO) index in late boreal winter on these time scales. Our data show that on decadal time scales a weaker Aleutian Low precedes a negative NAO by several years. This atmospheric link can explain the coherence of decadal North Pacific and Atlantic Multidecadal Variability, as suggested by earlier studies using climate models and limited instrumental data.  相似文献   

18.
Summary In this study the authors have developed a statistical method and have reconstructed Northern Hemisphere 500 hPa heights back to the late 19th century using one temperature and three sea level pressure (SLP) data sets. First, the relationship between ERA40 500 hPa heights and surface temperature and SLP was screened using stepwise multiple regression based on the calibration period of 1958–2002 (1998/2000 according to the availability of SLP data). All selected predictors (temperature and SLP) were significant and their variance contribution was greater than 1%. On average, there were 8.1 variables retained in the final regression equations. Second, the regression equations were applied to compute the 500 hPa height through to the late 19th century for the whole Northern Hemisphere. As the SLP and temperature coverage improved over time, the number of predictors decreased by about 1 in the most recent periods, and the root mean squared error decreased by about 0.8 m. A leave-one-out cross-validation method was used to test the skill and stability of the regression models. The reduction of error during the cross-validation period of 1958–1997 varied from 0.33 to 0.56, depending on the SLP data. Reconstructions were also checked using NCEP/NCAR 500 hPa heights from January 1949 to December 1957, and compared with the historical reconstruction over Europe. Reconstructions show high consistency with these independent data sets. Generally, the reconstruction provides a valuable opportunity to analyze, as well as to validate climate simulations of the variability in free atmosphere circulations over the past one hundred years.  相似文献   

19.
The aims of this study are to identify the trend of warm days and cold nights over the Iberian Peninsula and to connect the variations with large-scale variables. The reasons for performing this analysis are the effects that extremes events have on different ecosystems. Here, we present the results on spatial and temporal variability of warm days (TX90), or those exceeding the 90th percentile of maximum temperature, and cold nights (TN10), or those falling below the 10th percentile of minimum temperature. The extreme indices were derived from daily observations at stations and gridded data over land area for the period 1950 to 2006. Significant trends of more warm days and fewer cold nights were found. The trend to fewer cold nights is within the interval of global results given by the IPCC AR4 report; however, the trend to warm days is greater than the corresponding global trend. The influence of large-scale variables on these extreme indices was examined by means of the Empirical Orthogonal Function, correlation, composite maps and multiple regression analyses. Changes in TX90 are connected with the Scandinavian teleconnection index and a preferred mode of geopotential height at 500 hPa over the North Atlantic. Changes in TN10 are connected with the East Atlantic teleconnection index and the leading mode of Sea Surface Temperature (SST) variability over the North Atlantic area. Based on the links between the extreme indices and the large-scale variables we derived statistical models to describe the response of TX90 and TN10 to atmospheric circulation and SST variations. The models characterized the observed variations of TX90 and TN10 reasonably well. The results of this study encourage us to analyze, in further work, how temperature extremes might change over the Iberian Peninsula under warmer climate conditions.  相似文献   

20.
Daily meteorological observations have been made at the old astronomical observatory in Stockholm since 1754. Complete daily mean series of air temperature and sea level pressure are reconstructed from the observational data for 1756–1998. The temperature and pressure series arereconstructed and homogenized with the aid of metadata, statistical tests and comparisons with data from other stations. Comparisons with independently reconstructed daily series for nearby Uppsala (1722–1998) show that the quality of thedaily Stockholm data is good, although the reliability is lower before the mid-19th century. The daily temperature data show that the colder winter mean temperatures of the late 18th to early 19th centuries were connected with a particularly high frequency of very cold winter days. The warmer summers of the same period are more connected with a general shift of the temperature distribution towards higher temperatures than in the late 20th century.  相似文献   

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