Anticyclones

Atmospheric haze can occur over regions of several thousand square kUometers, caused by the oxidation of widespread SO2 and NO2 to sulfate and nitrate in relatively slow-moving air masses. In the eastern United States, large air masses associated with slow- moving or stagnating anticyclones have become sufficiently contaminated to be called hazy blobs. These blobs have been tracked by satellites as they develop and move across the country (15). 

Korshover (3) studied stagnating anticyclones in the eastern United States over two periods totaling 30 years. He found that for stagnation to occur for 4 days or longer, the high-pressure system had to have a warm core. Korshover s criteria included a wind speed of 15 knots or less, no frontal... 

Korshover, J., "Climatology of Stagnating Anticyclones East of the Rocky Mountains, 1936-1965," Public Health Service Publication No. 999-AP-34. U.S. Department of Health, Education and Welfare, Cincinnati, OH, 1967. 

Arid and semi-arid zones may be defined in several ways, but the climatic is the one most commonly accepted. According to that definition, aridity represents a lack of moisture in average climatic conditions (UNEP, 1993). This situation may be caused by one of four climatic conditions, which may interact in the case of specific arid/semi-arid zones continentality, topography, anticyclonic subsidence and oceanic cold currents. 

Currents in cyclonic gyres move water in a clockwise direction and counterclockwise in anticyclonic gyres. 

Piringer, M., E. Ober, H. Puxbaum, and H. Kromp-Kolb, Occurrence of Nitric Acid and Related Compounds in the Northern Vienna Basin during Summertime Anticyclonic Conditions, Atmos. Environ., 31, 1049-1057(1997). 

FIGURE 4.6 A typical weather map showing Europe and the North Atlantic. The closed curves are called isobars and are contours of constant atmospheric pressure. Regions of low pressure (L) are called cyclones and regions of high pressure (H) are called anticyclones. 

D4 0.460associated with subsidence inversion in anticyclonic situations. 

The first reported observations of elevated ozone levels in a European population centre date back over 40 years to July 1972 in London when hourly ozone levels in excess of 110 ppb were recorded [1], Shortly after this, elevated ozone levels were widely reported throughout northwest Europe during summertime anticyclonic conditions [2]. It soon emerged that a characteristic of these episodes was a rather uniform spatial distribution of elevated ozone levels over a large area of northwest Europe. Observations of elevated ozone levels at Adrigole, Ireland on the western seaboard of Europe confirmed the importance of the long-range transboundary formation and transport of elevated ozone levels [3]. 

The climate of the Sea of Azov, which deeply penetrates into land, is continental. It is characterized by cold winters, and dry and hot summers. In the autumn-winter period, the weather is determined by the influence of a spur of the Siberian anticyclone with a domination of easterly and northeasterly winds with a speed of 4-7 m/s. Enhancements of the impact of this spur cause strong winds (up to 15 m/s) and are accompanied by invasions of cold air masses. The mean monthly temperature in January ranges from - 1 to - 5 °C during northeasterly storms, it may fall down to - 25 to - 27 °C. 

The currents in the sea are mostly induced by the wind. Under the forcing by westerly and southwesterly winds, an anticlockwise water circulation in the sea is formed. The cyclonic water movement is also characteristic under easterly and northeasterly winds as well when they are stronger in the eastern part of the sea. If these winds are stronger in the southern part of the total abundance, the circulation has an anticyclonic character. At weak winds and calm, insignificant currents of intermittent directions are observed. Since weak and moderate winds dominate above the sea surface, currents with velocities lower than 10 cm/s feature the highest recurrence rates. Under strong winds up to 15-20 m/s, current velocities increase up to 60-70 cm/s. 

At the northerly processes, the Black Sea finds itself at the southeastern periphery of a vast anticyclone centered over Europe and Scandinavia. The strongest northerly winds accompany rapid displacement of the anticyclone from the region of the Balkan Peninsula in the course of the development of salinity activity over the Caucasus, the Caspian Sea, and, more rare, over the eastern part of the Black Sea. In these cases, the rate of atmosphere pressure growth in the western section of the Black Sea may reach 3-5 hPa during 3 h. 

At the northeasterly synoptic process in the Black Sea region, the center of the anticyclone is located over the western regions of the European part of Russia. Owing to the advection of cold air from the north and northeast, the cyclonic activity over the southeastern part of the Black Sea is intensified. The passage of cyclones over the southern part of the Black Sea is accompanied by strong easterly and northeasterly winds, especially in the northeast of the Black Sea and off the western coast of the Crimea. At the same time, the southeastern part of the sea is usually dominated by weak and moderate winds of different directions. 

For the easterly type of processes, it is characteristic of the anticyclone to be centered over the central regions of the European part of Russia. Meanwhile, the cyclonic activity also develops over the Mediterranean Sea and Turkey. In so doing, the Mediterranean cyclones tend to the southern regions of the Black Sea and result in a significant strengthening of easterly winds over the major part of its area. 

The northwesterly type of synoptic processes is related to the development of the cyclonic activity in the southeast of the European part of Russia and to an anticyclone over Europe with a spur toward the Balkan Peninsula. Similar to the westerly type of the process, the strongest winds are observed at the displacement of Scandinavian cyclones to the southeast of the European part of Russia across the southern part of the Ukraine in the rear of the Mediterranean cyclones. 

In the case where a cyclone is located over the central part of the Black Sea, strong easterly and westerly winds dominate over its northern and southern parts, respectively. At this time, an anticyclone is usually located over the European part of Russia. 

The Novorossiisk boras most often emerge when the center of the European part of Russia is occupied by an intensive cold anticyclone, at the southern margin of which strong northeasterly winds develop. Often, boras are induced in the rear parts of the so-called diving cyclones that travel from Scandinavia and Karelia to the Lower Volga or Southern Urals. In all these cases, the boras on the Black Sea coasts are related to the penetration of cold air into the southern part of the European part of Russia. Usually, boras are observed in the wintertime, while the most intensive events are confined to the end of the fall to the beginning of the winter, when the sea is still warm as in the summer, while invasions of very cold Arctic air from the continent are already possible. 

Atmospheric pressure. The regime of the atmospheric pressure over the Black Sea is defined by the influence of the Azores and Asian anticyclones, by the area of the wintertime cyclonic activity over the Mediterranean Sea, and by the summertime thermal depression over North Africa and Asia Anterior. Seasonal changes in the air and sea surface temperatures additionally affect the pressure field. In addition, cyclone passages may cause rather rapid and significant aperiodic changes it atmospheric pressure. 

Over the vast northwestern shelf, the above-listed schematics of the BSGC showed a cyclonic water motion with velocities up to 0.20 m s x. A special research study [6] helped to reveal a strong dependence of the shelf currents on the synoptic wind patterns and a domination of anticyclonic current vorticity in the summertime. 

The mean vectors of the winter and summer currents in the surface (0-40 m), subsurface (50-75 m), and intermediate (100-300 m) layers of the Black Sea are presented in Fig. 2. They confirm the cyclonic character of the BSGC in the winter and summer. Even at depths of 1,000 and 1, 500-m (not shown), southwest and southeast of the Crimea, where the currents feature relatively low velocities and diverse directions, in nine and five of the total 19 cases, cyclonically and anticyclonically directed vectors, respectively, were observed (in the remaining five cases, the vectors had quasimeridional directions). In the surface layer near the shore, anticyclonic vector directions were observed only three times twice in the wintertime off the Danube River mouth (see Fig. 2a) and once in the fall west of the Bosporus (not shown). These regions are known as areas of quasi-stationary NSAEs (see Fig. 1). 

In the near-shore zone, selected drifters were repeatedly captured by NSAE and performed anticyclonic rotation with velocities up to 0.60-0.80 m s-1 (in the Batumi NSAE) nevertheless, no one of these eddies was noted in the averaged schematic. 

In May (Fig. 8), the western SBCG, which displaced to the Bulgarian coast, becomes more intensive. South of the Crimea and off the middle part of the Caucasian coast, anticyclonic gyres develop they cannot be referred to as NSAEs, especially at a depth of 300 m (Fig. 8b). One of them is well manifested even at a depth of 1000 m (Fig. 8c), where the BSGC retains only its most general features intrinsic of it in the upper 300-m layer. 

E, the former Crimean, Kerch, and Batumi NSAEs almost merged to form a common anticyclonic water motion, although over a complicated meandering trajectory. 

The vertical structure of the zonal velocity components in the meridional sections across the eastern and western SBCGs is shown in Fig. 10. In March, the current structure is simpler than in September. In the eastern part of the sea, surface currents penetrate deeper than in the west. Locally, one can observe weak deep countercurrents beneath the surface streams however, there are no reasons to suggest a full change in the BSGC in the deep and, the more so, in the intermediate layers. Note that the climatic anticyclonic vorticity of the currents at the center of the Eastern Black Sea in September (Fig. lOd) is... 

In [50], the mean annual wind field compiled according to the data of the Russian Climatic Reference Book was used. The mean wind speeds became two to threefold higher. The maximums of the velocity and cyclonic vorticity of the wind were confined to the eastern part of the Black Sea. The almost twofold decrease in the horizontal grid step (11 km) as compared to [48] allowed one to reproduce in [50] a system of subbasin cyclonic and anticyclonic eddies quasiperiodic over the longitude it clearly dominated over the large-scale BSGC. The latter is represented in [50] only in the weaker mean annual current fields. 

The eddies were formed off the eastern coast of the Black Sea and moved westward showing a decrease in the phase velocity in the narrowest area of the sea south of the Crimea. In the model version with a flat abyssal floor at a depth of 1540 m, the wavelength comprised 250 km in the east and 190 km in the west with a period of 160 days and a phase velocity of - 2.0-2.5kmday-1. The orbital velocities in the eddies in the surface layer reached 0.45 ms 1 and deeper decreased down to 0.25 ms-1 a depth of 70m and to 0.05 - 0.10 m s 1 at a depth of 1100 m. The wave regime was more intensive in the eastern part of the Black Sea in its western part, eddies dissipated above the continental slope and partially reflected from the western coast. In the study [50], the introduction of the abyssal bottom topography increased (reduced) the sizes and intensities of cyclonic (anticyclonic) eddies by a factor of 1.5-2. The cyclonic (anticyclonic) eddies became more alike the SBCGs (NSAEs) in Fig. 1. The period of the eddies grew up to almost two years, while their phase velocity decreased down to 0.4-0.5 km day-1. 

Below 500 m, the BSGC is poorly studied it significantly differs from the surface pattern by low mean velocities (not higher than 0.01-0.03 ms-1) and a prevalence of mesoscale eddies with anticyclonic vorticity instantaneous velocities here may reach 0.30-0.40ms-1 only owing to short-period (inertial, etc.) motions. 

Keywords Black Sea Coastal anticyclonic eddies Coastal upwelling ... 

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