ALBERT

Description: Purpose. The dynamics of nonstationary, nonlinear, axisymmetric, warm-core geophysical surface frontal vortices affected by Rayleigh friction is investigated semi-analytically using the nonlinear, nonstationary reduced-gravity shallow-water equations. The scope is to enlarge the number of known (semi)analytical solutions of nonstationary, nonlinear problems referring to geophysical problems and even to pave the way to their extension to broader geometries and/or velocity fields. Methods and Results. The used method to obtain the solutions is based on the decomposition of the original equations in a part expressing their prescribed spatial structure, so that they can be transformed into ordinary differential equations depending on time only. Based on that analytical procedure, the solutions are then found numerically. In this frame, it is found that vortices characterized by linear distributions of their radial velocity and arbitrary structures of their section and azimuthal velocity can be described exactly by a set of nonstationary, nonlinear coupled ordinary differential equations. The first-order problem (i. e., that describing vortices characterized by a linear azimuthal velocity field and a quadratic section) consists of a system of 4 differential equations, and each further order introduces in the system three additional ordinary differential equations and two algebraic equations. In order to illustrate the behavior of the nonstationary decaying vortices and to put them in the context of observed dynamics in the World Ocean, the system’s solution for the first-order and for the second-order problem is then obtained numerically using a Runge-Kutta method. The solutions demonstrate that inertial oscillations and an exponential attenuation dominate the vortex dynamics: expansions and shallowings, contractions and deepenings alternate during an exact inertial period while the vortex decays. The dependence of the vortex dissipation rate on its initial radius is found to be non-monotonic: it is higher for small and large radii. The possibility of solving (semi)analytically complex systems of differential equations representing observed physical phenomena is rare and very valuable. Conclusions. Our analysis adds realism to previous theoretical investigations on mesoscale vortices, represents an ideal tool for testing the accuracy of numerical models in simulating nonlinear, nonstationary frictional frontal phenomena in a rotating ocean, and paves the way to further extensions of (semi-) analytical solutions of hydrodynamical geophysical problems to more arbitrary forms and more complex density stratifications.

Description: Purpose. The paper is aimed at obtaining the wave regime characteristics in the region of the Western Crimea accumulative coast, at constructing the scheme of the sediment along-coastal fluxes for various wind directions, at analyzing the previous notions on the lithodynamical processes in the region under study and their comparison with the obtained results. Methods and Results. The wave regime was analyzed using the results of the retrospective calculations of wind waves in the Black Sea derived due to the model SWAN and based on the ERA-Interim atmospheric reanalysis data for 1979–2018. The data of retrospective calculations performed by the method of annual maximums yielded the parameters of the waves of various repeatability. The sediment along-coastal flux was simulated and the schemes for six wind directions were constructed by the method including model values of the wave characteristics. Conclusions. Operative and extreme characteristics of the wind waves in the region under study are obtained. It is shown that in the above-mentioned area, the most intense sediment along-coastal fluxes occur being affected by the waves formed by the western, southwestern and southern winds. The northwestern and western winds give rise to the sediment main flux directed to the east. At the western wind, to the southeast from the Donuzlav sandbar and in the coast concavities, the sediments are transported in the opposite direction. When the winds are southwestern and southern, the sediment along-coastal flux move from the Cape Uret to Lake Donuzlav northern spit, where it meets the oppositely directed flux. To the southeast from Lake Donuzlav, the multidirectional fluxes arise; at that, in the coast concavities their convergence zones are formed. At the southeastern and eastern winds, the sediment along-coastal fluxes’ capacity decreases sharply; the fluxes are of multidirectional character and they form not a single flux on any of the long stretches of the coastline.

Description: Purpose. Investigation of the storm surge in Korsakov in the southern part of the Sakhalin Island on November 15, 2019 and comparison of the results of its numerical simulation with the data of in situ measurements constitute the aim of the article. Methods and Results. In situ measurements of the storm surge in Korsakov (the Sakhalin region) were performed and the data on the flooded area dimensions were collected. A storm period on the Sakhalin Island is almost the annual event in an autumn-winter season. The severe storm that happened in the southern Sakhalin region on November 15, 2019 led to flooding of the port territory in Korsakov. Due to the NAMI-DANCE computational complex, the storm surge was numerically simulated within the framework of the system of shallow water equations in the spherical coordinates on the rotating Earth with the regard for the friction force and the atmospheric effect. The calculations included the data on temporal and spatial distribution of the wind speed at the altitude 10 m taken from the Climate Forecast System Reanalysis database. The data on the atmospheric pressure were not applied in simulations since the atmosphere pressure gradient at the area under study was small. The simulation was carried out in the course of three days. The simulations showed that in 20 hours after the wind forcing had started, the water level in the port increased up to its maximum values, and did not fall the whole day. The water level maximum heights were concentrated in the southwestern part of the Aniva Bay. At that the calculated current speeds reached 2 m/s. During the storm, at the wind speed up to 15 m/s, the storm surge height in the Korsakov port area constituted 1.7 m, whereas the width of the flooded zone was up to 200 m. These results are confirmed well by the in situ measurement data. Conclusions. The simulation values of the power characteristics for the above-mentioned storm are represented in the paper. The Froude number square reaches 0.03 in the Korsakov city port area, and spatial distribution of the wave strength moment is up to 1 m3/s2. Field measurements and eyewitness reports confirm the evidence of a powerful impact of a storm surge upon the port constructions.

Description: Purpose. The paper describes development of a device (placed on the Arduino platform) for recording wind waves. It is intended for the wave gauge of Marine Hydrophysical Institute, RAS, which is installed and applied at the oceanographic platform in Katsiveli. The device is designed to record and store the wave gauge data in an off-line mode. At that, it is protected from power surges and environmental effects (dust, moisture, temperature drops). Methods and Results. Two versions of the Arduino-placed recording device are represented: for the single- and six-string wave gauges. Their hardware and software are described; block diagram of the applied software algorithms and electrical connection schemes are given. Particular attention is paid to stable functioning of the devices, namely continuity of the data reading, recording and storing, as well as synchronization of the obtained measurement results with the time of record. The example of the sea level elevations recorded in course of a year is cited. Conclusions. Development, construction and testing of the Arduino-placed device for recording wind waves are described in the paper. Since 2015, the off-line operation of the device has shown high efficiency, reliability and stability; at that, the risks of losing the measurement results are minimal.

Description: Purpose. The aim of the paper is to identify possible trends in the wave climate dynamics in the Baltic Sea, and to analyze statistical significance of the coefficients of these trends based on the results of their numerical modeling for 1979–2018. Methods and Results. The simulations for 1979–2018 (40 years) were carried out on an irregular grid using the MIKE 21 SW spectral wave model. The wind forcing was preset according to the ERA-Interim reanalysis data. The model was calibrated and validated against the data of wave buoys located in the northern and southern parts of the Baltic Sea. Based on the calibrated model, the wind wave parameters were calculated for the whole Baltic Sea area from 1979 to 2018 with the interval 1 hour. These parameters became the initial data for estimating temporal variability of the wind wave heights in the Baltic Sea for 40 years. The simulation results obtained on the irregular grid were interpolated to the regular one. It permitted to construct the maps of distribution of the maximum and average (for the 40-year period) significant wave heights in the Baltic Sea. The time trends for the average annual significant wave height values were revealed, and statistical significance of the coefficients of these trends was estimated. Conclusions. The average annual values of the significant wave heights over almost the whole Baltic Sea area for 1979–2018 (40 years) tend to decrease with the rate not exceeding 2–3 cm (2–3 %) per 10 years. The highest rate reduction is observed in the southeastern part of the Baltic Sea, the lowest – in the Gulf of Bothnia and the Gulf of Finland. Interannual variability of the average annual significant wave heights and the changes along the trend during the entire 40-years period are of the same order.

Description: Purpose. The paper is aimed at studying climatic trends in variability of the average annual and average monthly fields of significant wave heights of the mixed and wind seas, swell and the wind speeds in the Black Sea region. Methods and Results. Based on the MIKE 21 SW numerical model, the significant wave heights’ fields of the mixed and wind seas, and also swell were obtained for the period from 1979 to 2018. Long-term wind velocity changes were analyzed using the ERA-Interim reanalysis data for the same period. Linear climatic trends in the average annual and average monthly variability of the significant wave heights and the average wind speeds were evaluated by the statistical methods. Conclusions. The main feature of climatic variability of the significant wave height fields in the Black Sea is the pronounced spatial heterogeneity. In the western part of the sea, decrease in storm activity is observed. The eastern part is characterized by increase of the average significant wave heights. Statistically significant positive trends in fluctuations of the significant wave heights are observed in the coastal area from the Crimea southeast coast to the Georgia coast. Over the past 40 years, swell waves have intensified near the Turkish coast (to the east of Sinop) and near the Kerch Strait. The largest increase of the average monthly heights of mixed waves is observed in the eastern part of the sea in March and amounts 0.5–0.6 cm/year. This corresponds to increase of the average wind speeds by 0.025 m/s/year. In November, decrease of storm activity is observed in the western part of the sea that is expressed in diminution of the monthly average values of the significant wave heights by 0.8 cm/year. Decrease of the average annual wave heights by 0.08 cm/year is observed in the southwestern part of the Black Sea. On the contrary, the whole eastern part of the sea is subject to the increased storm activity accompanied by growth of the average annual wave heights in the fields of the mixed and wind seas by 0.10–0.15 cm/year. The above-mentioned features reflect climatic variability of the average wind speeds, which are characterized by wind weakening in the western part of the sea (0.010–0.015 m/s/year) and its amplification in the sea eastern part (0.015–0.020 m/s/year).

Description: Purpose. Morphodynamic system of the accumulative sandy coast can include one or more underwater bars. Position and shape of the underwater bar can reflect both seasonal changes of the coastal profile and its unidirectional movements landward and seaward. Determination of the character of the underwater bar movement under the influence of various wave conditions permits to reveal common factors of the coastal deposit multidirectional transport along the coast profile. Methods and Results. The results of field observations of morphodynamics of a section of the Baltic Spit sandy coast (600 m length) were analyzed. From May to November 2019, a series of measurements of the coastal zone relief were conducted. The obtained data were analyzed along with the wave regime parameters (reanalysis ERA5 data was used). The coastal profile of the area under study is complicated by the external underwater bar with its crest located at the depth 2.65 m, and by the internal one of a crescent shape. Conclusions. Analysis of displacement of the external underwater bar from May to November showed that this form was of a morphodynamics two-dimensional character, i.e. it possessed the same morphometric characteristics along the coast. It was revealed that the underwater bar crest was located at the depths close to those of wave breaking during the most recent relatively strong and sustainable storm. Based on this concept as well as on the available literature data on the relationship between a wave height and dynamics of an underwater bar crest, described is the landward displacement (recorded during the observation period) of the external underwater bar. Due to the field data, it was shown that the underwater bar morphodynamics was effected both by duration of individual waves and by difference between the wave parameters of a sequence of storm events.

Description: Purpose. The observation measurements testify the fact that heat and mass transfer processes in the shallow ice-covered lakes are not limited to the molecular diffusion only. In particular, the effective thermal diffusivity exceeds the molecular one by up to a few orders of magnitude. Now it is widely accepted that the transfer processes, in spite of their low intensity, are controlled by intermittent turbulence. At the same time, its nature and generation mechanism are still studied insufficiently. The paper represents one of such mechanisms associated with resonance generation of short internal waves by the barotropic seiches. Methods and Results. The temperature measurements in a shallow lake in winter were used as an experimental base. Having been analyzed, the temperature profiles’ dynamics observed during a few weeks after freezing revealed the anomalous values of thermal diffusivity. At that the temperature pulsations’ spectra clearly demonstrate the peak close to the main mode of barotropic seiches. Counter-phase oscillations at the different depths and pronounced heterogeneity of the amplitudes of temperature pulsations over depth indicate presence of internal waves. Based on these data, the mechanism of energy transfer from the barotropic seiches to the internal waves similar to the “tidal conversion” (the latter governs resonance generation of internal tides in the ocean), is proposed. The expressions for heat flux, energy dissipation rate and effective thermal diffusivity are derived. Conclusions. Internal waves can play an essential role in the processes of interior mixing and heat transfer in the ice-covered lakes. Though direct wind-induced turbulence production is inhibited, baric perturbations in the atmosphere can give rise to barotropic seiches, which play the role of an intermediate energy reservoir and can generate short resonant internal waves resulted from interaction with the undulate lake floor. The internal wave field parameters strongly depend on the barotropic seiche amplitudes, buoyancy frequency and the bottom topography features.

Description: Purpose. The aim of the paper is to study four synoptic situations, in which the seiches energy increase was observed in the coastal zone of the southern part of the Sakhalin Island, and to consider their possible meteorological origin. Methods and Results. Records of the waves obtained in the Institute of Marine Geology and Geophysics in 2008 using both the instruments installed in eight points in the coastal zone of the southern part of the Sakhalin Island, and the synoptic maps provided by the Sakhalin Hydrometeorological Service Department, were used. For all the observation points, four synoptic situations characterized by increase of the seiches energy within the meteotsunami existence range were considered. It is shown that the amplitudes of the main part of the observed waves exceed the criterion equal to 4 xrms. Therefore the events under consideration can be related to meteotsunami; at that, their energy is distributed almost all over the whole range of tsunami waves. When meteotsunami is absent, energy of the sea level oscillations in the range 4–120 min is reduced by an order. Since fluctuations are observed in the coastal zone possessing the resonant properties, arrival of meteotsunamis to these areas eventually results in exciting the seiches which are recorded. It is shown that in the coastal zone, cold fronts generate meteotsunamis, which, in their turn, give rise to seiches. Conclusions. The conditions for generating sea waves by the atmospheric disturbances within the range of the tsunami periods 2–120 minutes are described. It is found that movement of an extended cold front in the east-south direction leads to generation of the large-amplitude seiches in the region of the southern part of the Sakhalin Island, just where all the settlements are located. At a synoptic situation when two cold fronts are moving over the island, generation of high-amplitude seiches is possible in the places, near which a cold front is passing.