Hydrodynamic modeling of floods in Saint Petersburg considering the operating dam

The Baltic Sea level is computed from the BALT-P three-dimensional hydrodynamic model at the grid with the horizontal resolution of 2 nautical miles, and the computation for the top of the Gulf of Finland is provided at the grid with the spatial resolution of 90 m. The sea motion is induced by the air pressure gradients and wind stress values from the HIRLAM model forecast specified on the sea surface. The sea level is calculated for three floods in Saint Petersburg with account that each of eight spillways of the dam closed and opened not instantly but during the prescribed period of time. It is revealed that the BALT-P model simulates the sea level well during three floods in Saint Petersburg considering the operating dam. The model can be used for the sea level forecasting in Saint Petersburg based on the HIRLAM atmospheric model data with the lead time of 60 hours.     

Potential hydrometeorological threshold values of the coastal hazard—an example from the Polish Southern Baltic coast

This paper analyses the spatiotemporal variability of extreme hydrometeorological events at the Polish coast of the Baltic Sea. Extreme precipitation events and storm surges determine to the largest extent the contemporary transformations of sea coastal geoecosystems and represent the major factors that disturb their functioning. The statistical characteristics of these values were computed from the data of six meteorological and tide-gage stations located at the Baltic seaside. Daily data on the amount of precipitation and the sea level for the period of 1966–2009 were used for the study. Annual and daily maximum values of precipitation and sea level are presented for the Southern Baltic coast. The threshold values of the hydrometeorological parameters considered in the study allow assessing the hazard caused by the disturbance of the functional stability of the sea coastal geoecosystems.     

Wave interpretation of major Baltic inflows

The water dynamics in the straits between the North and Baltic seas during two major Baltic inflows that took place in the January of 1993 and 2003 is investigated using satellite altimetry data. It is found that the water mass surge to the eastern coast of the North Sea occurs before the beginning of the major Baltic inflow, and the sea level difference between the two seas is ~60 cm. Low-frequency fluctuations in the sea level and its wave parameters are studied. The wavelet analysis and the frequency-directed spectral analysis reveal the wave nature of the mechanisms leading to major Baltic inflows. The empirical characteristics of the obtained low-frequency waves are compared with the theoretical dispersion relations for the gradient-vorticity waves. Sea level variations during major Baltic inflows in the Danish Straits are identified as baroclinic Rossby waves. The analysis of cyclonic activity in the Northern Hemisphere demonstrated that stationary cyclones were observed during the inflows; this proves the feasibility of the resonance mechanism of the generation of major Baltic inflows.     

On the spatiotemporal structure and mechanisms of the Neva River flood formation

A comparative contribution of the sea level oscillations of various time scales (long-term, seasonal, synoptic, and mesoscale) to the formation of the Neva River floods is estimated. The identification of the Neva River flood waves as the long gravity ones existing nowadays is called in question. The comparison of estimated characteristics of flood waves with the theoretical variance relations of different types of long waves is carried out. This comparison as well as the results of analysis of meteorological information and numerical experiments carried out before on the basis of the hydrodynamic model of the Baltic Sea demonstrate that the Neva River flood waves are identified as the forced baroclinic topographic waves generated as a result of the resonance between the anemobaric forces in atmospheric cyclones and low-frequency eigenmodes of the open Baltic Sea-Gulf of Finland system.     

Baltic Sea climate in the late twenty-first century: a dynamical downscaling approach using two global models and two emission scenarios

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.     

Calculation of extreme water levels in the eastern part of the Gulf of Finland

An analytical expression is proposed for specifying atmospheric pressure in an idealized moving cyclone taking into account the existence of the cold front and the time evolution of cyclone intensity. Empirical parameters in this relation are determined for the most intense cyclone in the Baltic Sea region. The hydrodynamic model of the Baltic Sea with these parameters is used to evaluate extreme water levels in the eastern Gulf of Finland for different trajectories and propagation speeds of the cyclone. All results are obtained for the zero mean water level in the Baltic Sea.     

Spatial and Temporal Features of Synoptic and Mesoscale Variability of the Baltic Sea Level

The spatial and temporal features of synoptic and mesoscale variability of the Baltic Sea level are studied using long-term hourly data. The spectral analysis revealed significant difference in the structure of the sea level spectra between the Gulf of Bothnia and the Gulf of Finland. The maximum variance of the synoptic sea level variability is observed at the head of the Gulf of Bothnia and in the southwestern part of the Baltic Sea, whereas the maximum variance of mesoscale variability is registered at the head of the Gulf of Finland and in the southwestern part of the sea. The minimum variance of synoptic sea level variability was observed in the Gulf of Bothnia in the 1950s–1960s, and the maximum was recorded at the beginning and at the end of the 20th century. The series of interdecadal variability of synoptic sea level fluctuations have a weak negative trend up to ?0.11 cm²/year in Kungsholmfrost. A significant qualitative and quantitative correlation was detected between the interannual variability of variance of mesoscale sea level variations in the Gulf of Finland (Gornyi Institut) and the Gulf of Riga (Parnu) and the interannual variability of the NAO index.     

On the resonance-wave mechanism of major Baltic inflows

The features of the spatiotemporal variability of the sea level in the North and Baltic seas during the periods of formation of major Baltic inflows are investigated using the analysis of satellite altimetry data. It is demonstrated that dramatic drops in the sea level between the Baltic and North seas are observed during a few weeks before major inflows. A process of intensive inflows of the North Sea water to the Baltic Sea is accompanied not only by horizontal motions but also by vertical ones manifested in the increase in convergent flows in the North Sea and divergent flows in the Baltic Sea. A pronounced feature of the low-frequency dynamics of water of the North and Baltic seas is its wave structure. In both seas, low-frequency waves with the periods of 14–36 days propagate with the eastern component of the phase velocity along the isobaths and are identified as barotropic topographic Rossby waves. Phase velocities and lengths of low-frequency waves in the Baltic Sea are smaller by several times than those in the North Sea. Using the data of the analysis of meteorological information, a resonance-wave mechanism of generation of major Baltic inflows is studied.     

Determining cyclone trajectories and velocities leading to extreme sea level rises in the gulf of Finland

Results of numerical modeling of water level rises (floods) in St. Petersburg are given. Simulations were carried out with the CARDINAL numerical model. Roles of different mechanisms in flooding are estimated. Numerical experiments were done for an idealized round cyclone with parameters of the cyclone of January 9, 2005, when the water level rose to 239 cm in St. Petersburg (central pressure of the cyclone was 965–970 hPa and wind speed reached 30 m/s). Sea level rises are obtained for different paths of such a cyclone over the Baltic Sea and for different velocities of its propagation. The most dangerous paths and velocities are determined.     

Present-day and future precipitation in the Baltic Sea region as simulated in a suite of regional climate models

Here we investigate simulated changes in the precipitation climate over the Baltic Sea and surrounding land areas for the period 2071–2100 as compared to 1961–1990. We analyze precipitation in 10 regional climate models taking part in the European PRUDENCE project. Forced by the same global driving climate model, the mean of the regional climate model simulations captures the observed climatological precipitation over the Baltic Sea runoff land area to within 15% in each month, while single regional models have errors up to 25%. In the future climate, the precipitation is projected to increase in the Baltic Sea area, especially during winter. During summer increased precipitation in the north is contrasted with a decrease in the south of this region. Over the Baltic Sea itself the future change in the seasonal cycle of precipitation is markedly different in the regional climate model simulations. We show that the sea surface temperatures have a profound impact on the simulated hydrological cycle over the Baltic Sea. The driving global climate model used in the common experiment projects a very strong regional increase in summertime sea surface temperature, leading to a significant increase in precipitation. In addition to the common experiment some regional models have been forced by either a different set of Baltic Sea surface temperatures, lateral boundary conditions from another global climate model, a different emission scenario, or different initial conditions. We make use of the large number of experiments in the PRUDENCE project, providing an ensemble consisting of more than 25 realizations of climate change, to illustrate sources of uncertainties in climate change projections.     

Monitoring sea level changes

Future sea level rise arouses concern because of potentially deleterious impacts to coastal regions. These will stem not only from the loss of land through inundation and erosion, but also from increased frequency of storm floods, with a rising base level, even with no change in storm climatology, and from saltwater intrusion and greater amounts of waterlogging. Current sea level trends are important in formulating an accurate baseline for future projections. Sea level, furthermore, is an important parameter which integrates a number of oceanic and atmospheric processes. The ocean surface demonstrates considerable variability on diurnal, seasonal, and interannual time scales, induced by winds, storm waves, coastal upwelling, and geostrophic currents. Secular trends in sea level arise from changes in global mean temperature and also from crustal deformation on local to regional scales. The challenge facing researchers is how best to extract the climate signal from this noise.This paper re-examines recent estimates of sea level rise, discusses causes of variability in the sea level records, and describes methods employed to filter out some of these contaminating signals. Evidence for trends in long-term sea level records and in extreme events is investigated. Application of satellite geodesy to sea level research is briefly reviewed.     

Diagnosis and forecast of the Caspian Sea level with the operational hydrodynamic model

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.     

High resolution re-analysis for the Baltic Sea region during 1965–2005 period

Regional reanalysis database BaltAn65+ comprising meteorological data for Baltic Sea region for the time period 1965–2005 is described. For data assimilation and hindcasts, the numerical weather prediction model HIRLAM 7.1.4 is applied, with 11 km horizontal and 60-layer vertical resolution. Reanalysis includes three-dimensional weather analysis data. Standard surface observations and meteorological soundings together with ship and buoy measurements from WMO observational network are used in analysis. Boundary fields are obtained from ECMWF ERA-40 global re-analysis. The BaltAn65+ can be considered as a regional refinement of ERA-40 for Baltic Sea region, providing the historical weather and climate data with enhanced spatial resolution, which is main motivation for creation of this novel reanalysis database.     

On the sea level rise in the Russian part of the Vistula Lagoon

The peculiarities are studied of variations of average annual and extreme levels in the Russian sector of the Vistula Lagoon situated in the southeastern part of the Baltic Sea. The main regularity of interannual variations of averaged characteristics of the lagoon level is a steady trend towards their increase: the mean level increase is characterized by the linear trend increasing depending on the length of the series, from 1.7–1.9 mm/year (Baltiisk, 1860–2006; Kaliningrad, 1901–2006) to 3.6–3.7 mm/year (Kaliningrad, Baltiisk, Krasnoflotskoe, 1959–2006). On the sea coast (Pionerskii, 1959–2006), this trend in the second half of the 20th century amounted to 2.6 mm/year only. The obtained results illustrate the response of level variations in the Baltic Sea lagoons to the global climate warming and indicate that the long-term evolution of average characteristics of the Vistula Lagoon level cannot be explained only by the increase in the level of the World Ocean and adjacent seas intensified in recent decades but is caused by the changes in the wind load and precipitation in the catchment basin.     

Water balance modelling in the Baltic Sea drainage basin – analysis of meteorological and hydrological approaches

Summary Efforts to understand and simulate the global climate in numerical models have led to regional studies of the energy and water balance. The Baltic Basin provides a continental scale test basin where meteorology, oceanography and hydrology all can meet. Using a simple conceptual approach, a large-scale hydrological model of the water balance of the total Baltic Sea Drainage Basin (HBV-Baltic) was used to simulate the basinwide water balance components for the present climate and to evaluate the land surface components of atmospheric climate models. It has been used extensively in co-operative BALTEX (The Baltic Sea Experiment) research and within SWECLIM (Swedish Regional Climate Modelling Programme) to support continued regional climate model development. This helps to identify inconsistencies in both meteorological and hydrological models. One result is that compensating errors are evident in the snow routines of the atmospheric models studied. The use of HBV-Baltic has greatly improved the dialogue between hydrological and meteorological modellers within the Baltic Basin research community. It is concluded that conceptual hydrological models, although far from being complete, play an important role in the realm of continental scale hydrological modelling. Atmospheric models benefit from the experience of hydrological modellers in developing simpler, yet more effective land surface parameterisations. This basic modelling tool for simulating the large-scale water balance of the Baltic Sea drainage basin is the only existing hydrological model that covers the entire basin and will continue to be used until more detailed models can be successfully applied at this scale. Received November 24, 2000 Revised April 4, 2001     

Storm surges in the Western Baltic Sea: the present and a possible future

Globally-coupled climate models are generally capable of reproducing the observed trends in the globally averaged atmospheric temperature or mean sea level. However, the global models do not perform as well on regional/local scales. Here, we present results from four 100-year ocean model experiments for the Western Baltic Sea. In order to simulate storm surges in this region, we have used the General Estuarine Transport Model (GETM) as a high-resolution local model (spatial resolution ≈ 1?km), nested into a regional atmospheric and regional oceanic model in a fully baroclinic downscaling approach. The downscaling is based on the global model ECHAM5/MPI-OM. The projections are imbedded into two greenhouse-gas emission scenarios, A1B and B1, for the period 2000–2100, each with two realisations. Two control runs from 1960 to 2000 are used for validation. We use this modelling system to statistically reproduce the present distribution of surge extremes. The usage of the high-resolution local model leads to an improvement in surge heights of at least 10% compared to the driving model. To quantify uncertainties associated with climate projections, we investigate the impact of enhanced wind velocities and changes in mean sea levels. The analysis revealed a linear dependence of surge height and mean sea level, although the slope parameter is spatially varying. Furthermore, the modelling system is used to project possible changes within the next century. The results show that the sea level rise has greater potential to increase surge levels than does increased wind speed. The simulations further indicate that the changes in storm surge height in the scenarios can be consistently explained by the increase in mean sea level and variation in wind speed.     

Modelling sensible and latent heat fluxes over sea during unstable,very close to neutral conditions

During slightly unstable but still very close to neutral conditions new results from two previous investigations have shown a significant increase of sensible and latent heat fluxes over the sea. The vertical heat transport during these conditions is dominated by detached eddies originating at the top of the boundary layer, bringing relatively cold and dry air to the surface. This effect can be described in numerical models by either enhanced heat transfer coefficients for sensible and latent heat (Stanton and Dalton numbers respectively) or with an additional roughness length, added to the original roughness lengths for heat and humidity. Such new expressions are developed using turbulence measurements from the Baltic Sea valid for wind speeds up to 14 m s⁻¹. The effect of including the increased heat fluxes is investigated using two different numerical models: a regional three-dimensional climate model covering northern Europe, and a process-oriented ocean model for the Baltic Sea. During periods of several days, the latent heat flux can be increased by as much as 100 W m⁻². The increase in sensible heat flux is significantly smaller since the process is only of importance in the very near-neutral regime where the sensible heat flux is very small. The long-term average effect over the Baltic Sea is of the order of several W m⁻².     

海面风场订正对风暴潮数值模拟的影响

海洋模式在模拟风暴增水时对于风场的依赖性比较大,准确的风场模拟是正确模拟风暴潮的重要前提.用渤海海域4次典型的风暴潮个例,检验改良的渤海风场推算模式对风暴潮数值模拟的影响,分别用订正前后的风场驱动风暴潮数值模式得到逐时的渤海增水场,并与塘沽实测值比较表明:在4个过程中海面风场订正后风暴潮模式的模拟结果均得到了明显的改进...     

Statistical Modeling and Trend Detection of Extreme Sea Level Records in the Pearl River Estuary

Sea level rise has become an important issue in global climate change studies. This study investigates trends in sea level records, particularly extreme records, in the Pearl River Estuary, using measurements from two tide gauge stations in Macau and Hong Kong. Extremes in the original sea level records(daily higher high water heights) and in tidal residuals with and without the 18.6-year nodal modulation are investigated separately. Thresholds for defining extreme sea levels are calibrated based on extreme value theory. Extreme events are then modeled by peaks-over-threshold models. The model applied to extremes in original sea level records does not include modeling of their durations, while a geometric distribution is added to model the duration of extremes in tidal residuals. Realistic modeling results are recommended in all stationary models. Parametric trends of extreme sea level records are then introduced to nonstationary models through a generalized linear model framework. The result shows that, in recent decades, since the 1960 s, no significant trends can be found in any type of extreme at any station, which may be related to a reduction in the influence of tropical cyclones in the region. For the longer-term record since the 1920 s at Macau, a regime shift of tidal amplitudes around the 1970 s may partially explain the diverse trend of extremes in original sea level records and tidal residuals.