Upwelling in the north-western Black Sea during the period of summer-time warming

A numerical multilevel model based on primitive equations of sea thermohydrodynamics is applied to investigate the development of near-shore upwelling zones in the north-western Black Sea. Analysed are the results of eight numerical experiments on mapping the areas of upwelling and downwelling, depending on wind direction. The acquired data are matched up with the observations by the NOAA-11 satellite designed to measure sea surface radiation temperature twice a day. The numerical calculations are shown to agree with the remotely-sensed data. Translated by Vladimir A. Puchkin.     

Climatic investigations of the Black Sea using hydrological observations

Results of numerical experiments on the hydrodynamic diagnosis and adaptation of the Black Sea climatic hydrological fields are briefly summarized. The principal features of the water dynamics for each season are discussed. The intra-annual variability of the Black Sea rim current is indicated, along with the existence of an array of anticyclonic eddies at its periphery and anticyclonic vorticity below the halocline in the central basin where a flow, opposite in direction to the surface flow, is generated at large depths.Translated by Vladimir A. Puchkin.     

Coastal upwelling in the Gelendzhik area of the Black Sea: Effect of wind and dynamics

Long series data of a thermistor chain in the Black Sea coastal zone near Gelendzhik were analyzed. A thermistor chain installed 1 km offshore and at a depth of 22 m. There are full and incomplete upwelling events observed. The study of upwelling genesis based on: wind speed data from the NCEP/CFSR reanalysis and Gelendzhik weather station, velocity and direction of coastal currents measured by ADCP profiler moored on the bottom near the thermistor chain. Over the whole observation period (warm seasons of 2013–2015), more than 40 events of upwelling were registered four of them were full upwellings, when presence of under-thermocline water was observed near the sea surface. For every upwelling event, conditions prior to the changes in thermic structure, were analyzed. It is found that full upwelling generally occur under synergistic wind and current forcing. Fairly strong forcing of one of these factors is sufficient for partial upwelling to occur.     

A numerical experiment on modelling synoptic eddies in the Black Sea during the summer season

An energetically-balanced model has been used to perform an eddy-resolving experiment on the calculation of the baroclinic circulation in the Black Sea. As the initial and boundary conditions, historical data on the density and tangential wind stress for the summer season have been used. Following the integration of a set of model equations, an array of anticyclonic eddies formed on days 50–60 on the margins of the Black Sea rim current. Off the Caucasus, Crimean, and Bulgarian coast, anticyclonic eddies are shown to be quasi-stationary. The north-western Black Sea and Anatolia coastal zone are areas of Black Sea rim current instability, where synoptic eddies — both cyclonic and anticyclonic — are generated.Translated by Vladimir A. Puchkin.     

Experimental and numerical study of current-induced artificial upwelling

The aim of the current paper is to investigate hydrodynamic characteristics of the artificial upwelling induced by ocean currents. Experiments were performed in a flume at different density difference heads, horizontal current velocities and upwelling pipe diameters. A three-dimensional computational fluid dynamics (CFD) model was employed on wider range of parameters for further analysis. The performance of the numerical model has been confirmed by the experimental findings. The present results show that the volume flow rate of current-induced artificial upwelling is influenced by geometrical parameters and inclination angle of the pipe, the horizontal current velocity and vertical distribution of water density. In ideal two-layer density stratified water, the critical current velocity to generate upwelling linearly increases with the increase of the density difference, and the maximum rising height for upwelling is inversely proportional to the density difference. Feasibility analysis was taken by using current and density profiles of the East China Sea near Dongji Islands, which provides an useful reference for engineering practice.     

Observations of a cycle of intense coastal upwelling and downwelling at the research site of the Shirshov Institute of Oceanology in the Black Sea

The paper presents the results of joint analysis of the response of vertical temperature and current velocity profile distributions in the coastal zone of the Gelendzhik region of the Black Sea to strong wind forcing in the third ten-day period of September 2013. This forcing was caused by the propagation of an atmospheric cyclone, which first initiated coastal upwelling that was later replaced by downwelling. We formulate a criterion for the development of full coastal upwelling and demonstrate its efficiency. We assume that frequent events of incomplete coastal upwelling and downwelling are associated with changes in the water dynamics (variations in the intensity and direction of the alongshore current) generally not related to local wind forcing.     

Peculiarities of the Black Sea rim current near the Crimean coast

This paper discusses the quasi-stationary Black Sea rim current velocity field observed at seven points of the shelf area and continental slope in the vicinity of South Crimea from 6 June to 15 July, 1991. Current velocity fluctuations conditioned by the difference in atmospheric pressures over the eastern part of the sea and the western one, with the wind speed being 5 cm s⁻¹, have been studied. Inertial and seiche flows are described numerically. The peculiarities of the kinematics of the Black Sea rim current’s regular component have been scrutinized. Translated by Vladimir A. Puchkin.     

Influence of vertical motions on maintaining the nitrate balance in the Black Sea based on numerical simulation

The upwelling of deep water associated with the influence of cyclonic wind curl and the difference in the buoyancy of the inflows in the lower and upper water layers is observed in the central part of the Black Sea. The resulting vertical water motions contribute to the transport of ammonium to the upper boundary of the anaerobic zone. In the suboxic zone, ammonium is converted to nitrate via nitrite as a result of the nitrification, and thus it can supply the nitrocline in the water basin. Within the framework of this paper we discuss the effectiveness of this mechanism on the basis of the numerical simulation. The calculations were performed using a one-dimensional physical-biogeochemical model for the upper 600-m sea water layer, which takes into account seasonal variations in atmospheric parameters and vertical motions. The model describes the biological and redox processes in the suboxic zone. We have estimated the contribution of different constituents into the balance of nitrogen compounds in the euphotic water layer. It is shown that ammonium nitrogen coming from the deep water due to vertical water motion plays a significant role in maintaining the balance of nitrates in the central part of the Black Sea.     

Technique for Simulation of Black Sea Circulation with Increased Resolution in the Area of the IO RAS Polygon

A numerical technique is presented for simulating the hydrophysical fields of the Black Sea on a variable-step grid with refinement in the area of IO RAS polygon. Model primitive equations are written in spherical coordinates with an arbitrary arrangement of poles. In order to increase the horizontal resolution of the coastal zone in the area of the IO RAS polygon in the northeastern part of the sea near Gelendzhik, one of the poles is placed at a land point (38.35° E, 44.75° N). The model horizontal resolution varies from 150 m in the area of the IO RAS polygon to 4.6 km in the southwestern part of the Black Sea. The numerical technique makes it possible to simulate a large-scale structure of Black Sea circulation as well as the meso- and submesoscale dynamics of the coastal zone. In order to compute the atmospheric forcing, the results of the regional climate model WRF with a resolution of about 10 km in space and 1 h in time are used. In order to demonstrate the technique, Black Sea hydrophysical fields for 2011–2012 and a passive tracer transport representing self-cleaning of Gelendzhik Bay in July 2012 are simulated.     

Forecasting of tsunami wave heights at the Russian coast of the Black Sea

Forecasting of tsunami wave heights at the Russian coast of the Black Sea is discussed. Prognostic numerical calculations of tsunamis were carried out for the tsunami sources uniformly distributed in the Black Sea basin (a total of 55 events). Their results are compared with the results of numerical modeling of the historical events (in 1939 and 1966) and the data of not numerous measurements. A preliminary forecast is made on this basis for the tsunami wave heights along the Russian coast of the Black Sea.     

Peculiarities of Polluted Water Spreading from a Submarine Source in Stratified Coastal Environment

We study the spreading of wastewaters from an underwater source in a stratified coastal environment using the results of satellite monitoring and mathematical modeling. The problem is considered as applied to deepwater discharge in the region of Golubaya Bay of the Black Sea near Sebastopol. The main factors preventing upwelling of pollution to the sea surface are analyzed on the basis of a numerical model. It is shown that peculiarities of wastewater spreading depend on the character of stratification and velocity of the background current. The main factor influencing the uplift of these waters to the surface is the existence of water layers with high vertical gradients of water density. We reveal the structure of the wastewater field consisting of a plume and a jet extended in the direction of the background current, which is located in the density interface. If stratification is weak, the plume may reach the sea surface and form a local region of water pollution, which is recorded in multispectral satellite images. It is found that the mass of polluted waters is characterized by negative anomalies of temperature and salinity.     

Application of the ray technique to calculate the time of long wave propagation in the Black Sea

This paper provides calculations of the time of long surface gravity wave propagation in the Black Sea. The ray technique is used by the numerical model to calculate wave fronts with the seabed relief prescribed in tabular form on a rectangular grid. It is speculated how the derived estimates can be employed to predict tsunamis in the Black Sea.Translated by Vladimir A. Puchkin.     

Upwelling in the Alaskan Beaufort Sea: Atmospheric forcing and local versus non-local response

The spin up and relaxation of an autumn upwelling event on the Beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models. The event occurred in November 2002 and was driven by an Aleutian low storm. The wind field was strongly influenced by the pack-ice distribution, resulting in enhanced winds over the open water of the Chukchi Sea. Flow distortion due to the Brooks mountain range was also evident. Mooring observations east of Barrow Canyon show that the Beaufort shelfbreak jet reversed to the west under strong easterly winds, followed by upwelling of Atlantic Water onto the shelf. After the winds subsided a deep eastward jet of Atlantic Water developed, centered at 250 m depth. An idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm. The disparity in wave speeds between the sea surface height signal—traveling at the fast barotropic shelf wave speed—versus the interior density signal—traveling at the slow baroclinic wave speed—leads to the deep eastward jet. The broad-scale response to the storm over the Chukchi Sea is investigated using a regional numerical model. The strong gradient in windspeed at the ice edge results in convergence of the offshore Ekman transport, leading to the establishment of an anti-cyclonic gyre in the northern Chukchi Sea. Accordingly, the Chukchi shelfbreak jet accelerates to the east into the wind during the storm, and no upwelling occurs west of Barrow Canyon. Hence the storm response is fundamentally different on the Beaufort slope (upwelling) versus the Chukchi slope (no upwelling). The regional numerical model results are supported by additional mooring data in the Chukchi Sea.     

Ventilation of the Black Sea pycnocline. Parameterization of convection, numerical simulations and validations against observed chlorofluorocarbon data

Data from field observations and numerical model simulations are used to understand and quantify the pathways by which passive tracers penetrate into the Black Sea intermediate and deep layers. Chlorofluorocarbon (CFC) concentrations measured during the1988 R.V. Knorr cruise show strong decrease with increasing density in the Black Sea and illustrate the very slow rate of ventilation of deep water in this basin. We develop a 3D numerical model based on the Modular Ocean Model (MOM), and calibrate it in a way to produce consistent simulations of observed temperature, salinity and CFCs. One important feature is the implementation of a special parameterization for convection, which is an alternative of the convective adjustment in MOM and handles the penetration of the Bosporus plume into the halocline. The model forcing includes interannually variable wind, heat and water fluxes constructed from Comprehensive Ocean–Atmosphere Data Set and ECMWF atmospheric analysis data and river runoff data. The analysis of observations and simulated data are focused on correlations between thermohaline and tracer fields, dynamic control of ventilation, and the relative contributions of sources at the sea surface and outflow from the Bosporus Strait in the formation of intermediate and deep waters. A simple theory is developed which incorporates the outflow from the strait along with the vertical circulation (vertical turbulent mixing and Ekman upwelling) and reveals their mutual adjustment. The analyses of simulated and observed CFCs demonstrate that most of the CFC penetrating the deep layers has its source at the sea surface within the Black Sea rather than from the Marmara Sea via the Bosporus undercurrent. Under present-day conditions, the surface CFC signals have reached only the upper halocline. Intrusions below 600 m are not simulated. The major pathways of penetration of CFCs are associated with cold-water mass formation sites, Bosporus effluent, as well as with the diapycnal mixing in the area of Rim Current. Future CFC sampling strategies coherent with the unique conditions in the Black Sea are discussed.     

Characteristics and influencing factors of frontal upwelling in the Yellow Sea in summer

Frontal upwelling is an important phenomenon in summer in the Yellow Sea (YS) and plays an essential role in the distribution of nutrients and biological species. In this paper, a three-dimensional hydrodynamic model is applied to investigate the characteristics and influencing factors of frontal upwelling in the YS. The results show that the strength and distribution of frontal upwelling are largely dependent on the topography and bottom temperature fronts. The frontal upwelling in the YS is stronger and narrower near the eastern coast than near the western coast due to the steeper shelf slope. Moreover, external forcings, such as the meridional wind speed and air temperature in summer and the air temperature in the preceding winter and spring, have certain influences on the strength of frontal upwelling. An increase in air temperature in the previous winter and spring weakens the frontal upwelling in summer; in contrast, an increase in air temperature in summer strengthens the frontal upwelling. When the southerly wind in summer increases, the upwelling intensifies in the western YS and weakens in the eastern YS. The air temperature influences the strength of upwelling by changing the baroclinicity in the frontal region. Furthermore, the meridional wind speed in summer affects frontal upwelling via Ekman pumping.     

Observational characteristics and dynamic mechanism of low-salinity water lens for the offshore detachment of the Changjiang River diluted water in August 2006

The Changjiang River diluted water(CDW) spreads into the East China Sea(ECS) primarily in a plume pattern,although in some years, low-salinity water lenses(LSWLs) detach from the main body of the CDW. In-situ observations indicate that in August 2006, a LSWL detached from the main body of the CDW near the river mouth.In this paper, the effects of winds, tides, baroclinity and upwelling on LSWLs are explored with a threedimensional model. The results show that:(1) winds play a crucial role in these detachment events because windinduced northerly Eulerian residual currents impose an uneven force on the CDW and cut it off, thus forming a LSWL;(2) upwelling carries high-salinity water from the lower layer to the upper layer, truncating the low-salinity water tongue vertically, which is conducive to the detachment and maintenance of LSWLs; and(3) upwelling during the evolution of a LSWL is caused by the combined effects of winds and tides. The influences of windinduced upwelling are mainly near the shore, whereas the upwelling along the 30 m isobath is predominantly affected by tides, with the effect increasing from neap tide to spring tide.     

Upwelling in the northwest part of the Black Sea at the end of the summer season and its causes

By using the archival data of routine hydrometeorological and satellite observations, we perform the analysis of the general regularities of manifestations of upwelling in the anomalies of the surface temperature in the northwest part of the Black Sea at the end of the summer season. We describe the structure of coastal upwelling according to the data of a hydrological survey carried out in the Kalamitskii Bay in September 2007 characterized by the extremely intense anomalies of sea surface temperature. By using the data of reanalysis on the heat fluxes and the wind field, we analyze the cause-effect relations responsible for the evolution of this upwelling.     

Modeling of Long-Term Evolution of Hydrophysical Fields of the Black Sea

The long-term evolution of the Black Sea dynamics (1980–2020) is reconstructed by numerical simulation. The model of the Black Sea circulation has 4.8 km horizontal spatial resolution and 40 levels in z-coordinates. The mixing processes in the upper layer are parameterized by Mellor-Yamada turbulent model. For the sea surface boundary conditions, atmospheric forcing functions were used, provided for the Black Sea region by the Euro mediterranean Center on Climate Change (CMCC) from the COSMO-CLM regional climate model. These data have a spatial resolution of 14 km and a daily temporal resolution. To evaluate the quality of the hydrodynamic fields derived from the simulation, they were compared with in-situ hydrological measurements and similar results from physical reanalysis of the Black Sea.     

南海形成演化探究

通过分析前人对南海的研究,对南海扩张期次、扩张脊结构、动力来源等几个关键研究问题进行探讨。认为应将南海放入到欧亚板块、印度一澳大利亚板块和太平洋板块三大板块相互作用的统一构造应力场中进行研究。利用FLAC软件,首次对南海及邻区进行数值模拟分析,并进一步探讨了南海的形成演化机制,认为南海的打开和扩张是印度板块与欧亚板块的碰撞、地幔柱上涌以及太平洋板块向欧亚板块的俯冲共同作用的结果。     

Numerical modeling of quasi-two-dimensional vortices in the atmosphere over the Black Sea

We consider quasi-two-dimensional rapidly dissipating mesoscale atmospheric vortices generated over the Black Sea near the Crimean and Caucasian coasts. Based on the results of numerical modeling for a characteristic example of the Crimean eddy, we determine its structure and parameters and estimate the rate of decay of kinetic energy and enstrophy. In addition to the large-scale secondary circulation in the vortex, we also consider a small-scale secondary circulation induced by Raleigh-Bénard convection.