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.     

Regional features of long-term variability of the Black Sea surface temperature

The regional features oflong-term variability ofsea surface temperature (SST) in the Black Sea are analyzed using the satellite data for 1982-2014. It is demonstrated that the maximum intraannual and interannual variability of SST is registered on the northwestern shelf of the Black Sea. The high level of interannual variability of SST and maximum linear trends are observed in the northeastern part of the sea. The qualitative connection is revealed between the long-term variability of SST and the variations in the intensity of the Black Sea Rim Current in the long-term seasonal cycle. An increase in the level of interannual variability of SST is observed in summer, when the Black Sea Rim Current weakens. The significant negative correlation is revealed between the interannual anomalies of SST and the NAO index. The highest correlation coefficients are obtained for the eastern part of the Black Sea and near the Crimean coast.     

The influence of momentum advection on the Baltic Sea dynamics

Contribution of momentum advection to the formation of the low frequency fields of the Baltic Sea levels and currents is estimated using numerical experiments with a hydrodynamic model and statistical analysis of the experimental results. It is found that momentum advection has a significant influence on the formation of the mean level and its seasonal and synoptic variability in Neva Bay of the Gulf of Finland. The results show that nonlinear effects associated with advective accelerations can essentially contribute to the Neva River flood formation.     

Crossings of ice-bound sea surfaces in history

Seven more-or-less well documentated cases of the use made of icebound sea areas in winter for the purposes of warfare are reviewed. The sea-ice crossings took place in 1495, 1577, 1581, 1658, 1809, 1940, and 1943, i.e. the first five occurred during the Little Ice Age. A book authored by a prominent Swedish personality (Archbishop Olaus Magnus) and published in 1555 says that warfare on frozen sea areas in winter by the Muscovites (Russians) and Swedes was as common as warfare by ships on the open seas in summer. There are indications of some crossings of ice-bound seas prior to 1495 and not necessarily for warlike activities. It seems that the Vikings too did some sea-ice crossings.The crossings of 1495, 1577, 1581, and 1940 involved the Gulf of Finland, that of 1809 the Gulf of Bothnia and the Aaland Islands area of the Baltic, that of 1658 the Danish Belts, and that of 1943 the Gulf of Taganrog in the Sea of Azov. In the first three cases the powers concerned were Muscovy (Russia) and Sweden which for centuries were fighting for supremacy in the Baltic and over the routes from the inner Baltic (Gulf of Finland and Bay of Riga) to western Europe. The case of 1809 involved, again, Russia and Sweden, though in the background of the conflict between the two were wider European issues of the Napoleonic wars. The 1658 crossing of the frozen-over Danish Belts was accomplished by the Swedes, forcing the Danes into submission: In the ensuing Peace Treaty Sweden for the first time in her history achieved her present territorial extent in the Scandinavian Peninsula. The case of 1940 was connected with the 1939–40 Winter War of Soviet Russia against Finland. The crossing of 1943 was made by German forces retreating from the Caucasus under the pressure of Soviet forces in World War II.The crossings of 1577, 1581, 1658, 1809, 1940, and 1943 took place between late in January and late in March; the case of 1495 appears to have taken place early in the winter season: probably late in November. Since in the period 1931–60 no part of the Gulf of Finland froze over before about the middle of December, the early date of the crossing of 1495 is possibly one of the many indications of cold winters during the Little Ice Age.     

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.     

Estimation of multi-scale temporal variability of air and water temperature in the northeastern part of the Black Sea

Standard deviations of mesoscale, synoptic, seasonal, and interannual fluctuations of the air and water temperature are calculated from long-term measurements. The contributions of each type of fluctuation to the total temporal variability are estimated. The intraannual cycle of variability of monthly (long-term) means of mesoscale and synoptic fluctuations is considered.     

The stochastic weather model in the system of deterministic and stochastic modeling of runoff and nutrient load

The estimation is carried out of the distribution functions of annual runoff and nutrient load on the Russian part of the Gulf of Finland (the Baltic Sea) formed by different pollution sources. The stochastic weather model is used for the estimation.     

Simulation of the probable maximum flood in the area of the Leningrad Nuclear Power Plant with account of wind waves

At the designing of nuclear power facilities at the coastal sites the risk of their flooding caused by the combinations of adverse hydrometeorological events should be assessed with the probability of exceedance to 0.01%. According to the IAEA recommendations, the combination of statistical and deterministic methods was used to calculate the flood level of such rare occurrence. The level of flooding caused by the storm surge and reiated wind waves were computed with the probability of 0.01% for the coastal part of the Koporye Bay of the Gulf of Finland in the area of the Leningrad Nuclear Power Plant 2 (LNPP 2) construction; the results are presented. The calculations are based on the CARDINAL and SWAN software and four nested numerical models (for the Baltic Sea, the eastern part of the Gulf of Finland, the Koporye Bay, and a part of the bay in the area of LNPP). The decrease in sea-surface drag coefficient at hurricane winds is taken into account.     

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.     

Mesoscale Wind Field Modifications over the Baltic Sea

For two consecutive days during spring 1997, the windfield over the Baltic Sea has been studied. Thestrength of the geostrophic wind speed is the majordifference in synoptic conditions between these twodays. During both days, the mesoscale wind field overmost of the Baltic Sea is quite heterogeneous; themodifications primarily being caused by the land-seacontrasts. On the day with the weaker wind speed,sea-breeze circulations develop. As a consequence, thewind direction at lower levels is more or lessopposite to the geostrophic over large areas of theBaltic Sea and the surface wind speed decreases withoffshore distance. Wind speed maxima caused by the seabreezes are found along the east coasts in the studiedarea. For the other day, the slow growth of a stableinternal boundary layer over the sea also gives asurface wind speed decrease with offshore distancefrom the coast.     

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.     

Interannual variability of water transport by the East Kamchatka and East Sakhalin Currents and their influence on dissolved oxygen concentration in the Sea of Okhotsk and subarctic pacific

The influence of interannual variability of water transport by the East Kamchatka Current, the Oyashio, and the East Sakhalin Current on the dissolved oxygen concentration in the western subarctic Pacific and the Sea of Okhotsk is considered for studying climate change impact on sea water chemical parameters. It is shown that statistically significant relation is observed between the calculated with the Sverdrup equation interannual variations in water transport with the East Kamchatka Current, the Oyashio, and the East Sakhalin Current and changes in mean sea water level at coastal stations in winter. It is found that the main reason of interannual variability of the dissolved oxygen concentration at isopycnic surfaces in the intermediate water layer (100–800 m) of the Sea of Okhotsk and in the western subarctic Pacific is caused by variations in water transport by the East Kamchatka Current, the Oyashio, and the East Sakhalin Current.     

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.     

The influence of the North Atlantic on climate variations in the Barents Sea and their predictability

The effects of Atlantic water inflow on the climate variability in the Barents Sea are studied. Initial data are the series of water temperature at the Kola meridian cross-section, monthly values of ice extent, air temperature at the stations, sea level pressure from the reanalysis data, and sea surface temperature. The methods of multivariate correlation, spectral, and factor analysis and EOF decomposition are used. It was found that variations in the Atlantic water inflow define the main part of interannual variability of sea ice extent, water temperature, and air temperature in the Barents Sea in the cold season. The influence of regional atmospheric circulation on the interannual variability of these parameters is small. The effects that water temperature anomalies in the area of Newfoundland and in the equatorial part of the North Atlantic have on climate parameters in the Barents Sea are discovered. The response of these parameters lags behind the respective anomalies by 9-58 months. The high correlation between them makes it possible to develop the method of statistical forecasting of sea ice extent and water temperature in the Barents Sea with the lead time up to 4 years.     

Observations of a quasi-tropical cyclone over the Black Sea

A rare atmospheric phenomenon in the Black Sea region is described: a mesoscale cyclone with all main properties of tropical cyclones. The cyclone developed in the southwestern part of the sea and existed for about five days. General characteristics of the cyclone are presented along with its effect on thermodynamic structure of the sea upper layer.     

Classification of atmospheric processes over the South China Sea

The classification is made of atmospheric circulation over the South China Sea water area for the period from 2000 to 2008 on the basis of daily surface synoptic charts taking account of the movement of cyclones and location of anticyclones. Three typical situations are marked out: low-gradient field, low-gradient field with the strong wind in the north of the sea, and the tropical cyclone appearance including three subtypes (the cyclone in the north, at the center, and in the south of the sea). The repeatability, continuity, and duration of the action of the types of atmospheric processes are computed as well as their seasonal and interannual variability.     

The Secondary Sea Level Maximum during Floods in Saint Petersburg and Its Simulation with Numerical Models

The study considered two- and three-dimensional models used to compute the Baltic Sea level. It is demonstrated for three floods that the BALT-P three-dimensional hydrodynamic model and the INMOM three-dimensional hydrothermodynamics model successfully simulate extreme sea level fluctuations during the floods in Saint Petersburg. To simulate extreme sea level fluctuations in the Baltic Sea, it is appropriate to use the BALT-P model which requires less input information. The analysis of simulation data for the considered cases reveals that the reason for the occurrence of the second flood maximum is the excitation of the wind-induced fundamental single-node seiche of the Baltic Sea.     

下垫面热力作用对黄海春季海雾的影响——观测与数值试验

利用海上浮标站、高分辨率数字式探空仪等多种观测手段和中尺度模式WRF,对2008年5月2—3日黄海发生的一次海雾过程进行了观测分析和数值模拟。观测表明,出现海雾时,气温明显下降,气海温差(海表面以上2 m气温减海表面以下1m水温)减小,不足0.5℃,浓雾时,甚至出现海温(SST)高于气温的现象。较强的湍流活动出现在大气边界层低层150 m以下。反映了低层大气稳定性减弱,可能有利于海雾的维持。海雾消散阶段,海气温差明显加大,湍流强度减弱,湍流发展高度升高。海雾过程中,可能存在动量下传的局地海-气相互作用机制,SST的升高可使雾中能见度好转。数值模拟的结果与观测基本一致,雾区内的气海温差明显小于雾区外,敏感性试验进一步表明:100 m以下气层稳定性和湍流发展条件对SST的变化敏感。SST的变化对稳定度的影响和对雾区范围的影响与近海面的水汽含量有关:在湿度较小(q0.5 g/kg)的薄海雾区,SST增加1℃,稳定度明显减弱(θ_v/z≤0.01 K/m),海雾面积缩小;SST下降1℃,稳定度增加(θ_v/z≥0.07 K/m),薄海雾面积增大。在湿度较大(q0.6 g/kg)的浓海雾区,SST的变化对静力稳定度的影响不大,海雾仍然维持。因此,当海气温差减小,甚至出现SST高于气温时,如果仍然有海雾,则一般是水汽含量比较大的浓海雾。该结果有助于对海雾形成机制的认识。     

Synoptic volumetric variations and flushing of the Tampa Bay estuary

Two types of analyses are used to investigate the synoptic wind-driven flushing of Tampa Bay in response to the El Niño-Southern Oscillation (ENSO) cycle from 1950 to 2007. Hourly sea level elevations from the St. Petersburg tide gauge, and wind speed and direction from three different sites around Tampa Bay are used for the study. The zonal (u) and meridional (v) wind components are rotated clockwise by 40° to obtain axial and co-axial components according to the layout of the bay. First, we use the subtidal observed water level as a proxy for mean tidal height to estimate the rate of volumetric bay outflow. Second, we use wavelet analysis to bandpass sea level and wind data in the time–frequency domain to isolate the synoptic sea level and surface wind variance. For both analyses the long-term monthly climatology is removed and we focus on the volumetric and wavelet variance anomalies. The overall correlation between the Oceanic Niño Index and volumetric analysis is small due to the seasonal dependence of the ENSO response. The mean monthly climatology between the synoptic wavelet variance of elevation and axial winds are in close agreement. During the winter, El Niño (La Niña) increases (decreases) the synoptic variability, but decreases (increases) it during the summer. The difference in winter El Niño/La Niña wavelet variances is about 20 % of the climatological value, meaning that ENSO can swing the synoptic flushing of the bay by 0.22 bay volumes per month. These changes in circulation associated with synoptic variability have the potential to impact mixing and transport within the bay.