Andrey Zatsepin

The West African coastal upwelling filaments and cross-frontal water exchange conditioned by them

One of the important problems in the oceanography of the wind-driven upwelling regions of the Ocean is the investigation of water exchange processes in the coastal zone. Satellite data (thermal and colour imagery) have changed our view on these processes after the relatively recent discovery of cold, chlorophyll-rich, narrow (< 50 km wide) offshore flowing filaments off the west coasts of North America, North and South Africa. On the basis of satellite IR images and oceanographic original and archive data we investigated systems of filaments in the northwest and southwest African upwelling regions. The spatial distribution of filaments was analyzed. It was found that seasonal variability of the filaments location depends upon the general intensity of upwelling motion along the coast during the year. The main statistical characteristics of filaments were obtained. An example of the three-dimensional velocity structure of the filament was presented. In order to estimate the intensity of cross-frontal exchange process due to filaments, a special procedure was proposed. The values of the velocity of cross-frontal water exchange produced by filaments in these upwelling zones are obtained. It was shown that upwelling filaments play an important role in water exchange between the coastal zone and the open ocean. A non-dimensional parameter which characterizes the permeability of oceanic fronts for water exchange due to mesoscale dynamical structures was introduced and estimated.

Frazil ice formation due to difference in heat and salt exchange across a density interface

Abstract Earlier qualitative laboratory studies of frazil ice formation in fresh water layers at 0°C cooled from below by a more saline sublayer have shown that the rate of freezing considerably increases in the case of external stirring of the fluid layers. In order to establish a basis for physical understanding and quantitative description of the effect discovered an experimental investigation of the process of heat and salt exchange across the density interface between turbulent layers was carried out. It is found that moderate turbulence greatly increases the fluxes across the density interface, but there remains still some difference in the velocities of heat and salt exchange for the range of themain non-dimensional parameters investigated. Estimates based on the experimental results show that the rate of freezing in the presence of turbulence in the layers may be some orders of magnitude greater than in the case of pure double diffusion. It is suggested that the most iintense frazil ice formation in the contact zone between fresh and salt water in polar regions takes place when both fluid layers are in a turbulent state of motion.

Variability of Wind-Driven Coastal Upwelling in the North-Eastern Black Sea in 1979–2016 According to NCEP/CFSR Data

This paper presents the variability of wind-driven upwelling based on results of the coastal upwelling criterion analysis for the Gelendzhik region of the Black Sea for 1979–2016xa0years. The calculations of the criterion are based on the wind data from reanalysis of NCEP-CFSR. The proposed method is used for the analysis of long-term upwelling variability in the Black Sea for the first time. This method allows detecting both full and incomplete upwelling in contrast to measurements of the sea-surface temperature (SST) on regular coastal weather stations or on satellites. Current study shows more than 100 cases of the upwelling (when upwelling criterionu2009<u2009−xa01) for 37xa0years in total, and some of them were confirmed with a satellite images. Comparison of the SST from Gelendzhik meteostation and upwelling criterion revealed that 70% of the upwelling cases are related to decrease of the temperature on sea surface. It is shown that the highest probability of wind upwelling events is detected in the mid-summer period. Interannual variability of the coastal upwelling criterion is very high, there was 1 year (2010) when no upwelling cases were registered, and maximum 8 cases are registered for 1987xa0year. There are three cases of upwelling on average per year. The process of the coastal upwelling depends on wind impact, but also on direction and strength of the coastal current. Study of the upwelling and its variability is necessary to supplement knowledge about coastal dynamic processes that affect the ecosystem and the recreational potential of the region.

GPS-drifters for study of water dynamics in the Black Sea shelf zone

This paper presents the description of a monitoring system based on drifters equipped with GPSreceiver and cellular GSM. The system provides data about currents with a temporal and spatial resolution of 5–10 minutes and 100–200 m. The movement of the drifter can be observed in real time. Several experiments were conducted on the Black Sea shelf for identification of the advantages of the monitoring system. The results of experiments include a comparison of the drifter trajectories with bottom-tracked ADCP and towed ADCP data.

Development of microstructure measurements meeting the Baltic Sea conditions

The principal physical research tasks addressing environmental problems of the Baltic Sea are the study of ventilation of the deep water and of vertical mixing. To achieve a progress, direct measurements of fine- and microstructure of water are necessary. Instrumentation to do this has been developed successfully; nevertheless the water structure in the Baltic Sea is so tricky that existing techniques need special adaptation and improvement. This paper presents several types of profilers: cycling profilers both towed and moored, and freely sinking or floating probes. Some of them perform direct microstructure measurements while others are necessary to obtain a properly resolved background measurement of thermohaline and current structure. We consider freely-moving CTDs as an alternative for direct dissipation measuring meters if the probes motion is stable enough and its spatial resolution is high enough. Having in mind the Baltic conditions, special attention is paid to fine measurements close to the sea surface and within the bottom boundary layer. We try to adjust such instruments for use from small inexpensive boats, so we hope fine- and microstructure measurements will be more accessible.