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Circulations in the vertical and horizontal planes
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The vertical change of pressure with height depends on the temperature structure. High-(low-) pressure systems intensify with altitude in a warm (cold) air column; thus warm lows and cold highs are shallow features. This 'thickness' relationship is illustrated by the upper-level subtropical anticyclones and polar vortex in both hemispheres. The intermediate mid-latitude westerly winds thus have a large 'thermal wind' component. They become concentrated into upper tropospheric jet streams above sharp thermal gradients, such as fronts.
The upper flow displays a large-scale long-wave pattern, especially in the northern hemisphere, related to the influence of mountain barriers and land-sea differences. The surface pressure field is dominated by semi-permanent subtropical highs, sub-polar lows and, in winter, shallow cold continental highs in Siberia and north-western Canada. The equatorial zone is predominantly low pressure. The associated global wind belts are the easterly trade winds and the mid-latitude westerlies. There are more variable polar easterlies and over land areas in summer a band of equatorial westerlies representing the monsoon systems. This mean zonal (west-east) circulation is intermittently interrupted by 'blocking' highs; an idealized sequence is known as the index cycle.
The atmospheric general circulation, which transfers heat and momentum polewards, is predominantly in a vertical meridional plane in low latitudes (the Hadley cell), but there are also important east-west circulations (Walker cells) between the major regions of subsidence and convective activity. Heat and momentum exchanges in middle and high latitudes are accomplished by horizontal waves and eddies (cyclones/anticyclones). Substantial energy is also carried polewards by ocean current systems. Surface currents are mostly wind driven, but the slow deep ocean circulation (global conveyor belt) is due to thermohaline forcing.
Упражнение 10.
Найдите в каждом предложении текста Circulations in the vertical and horizontal planes подлежащее и сказуемое. Определите время и залог сказуемого.
Упражнение 11.
Письменно переведите текст. (Контрольное время – 30 минут)
The trade winds
The trades (or tropical easterlies) are important because of the great extent of their activity; they blow over nearly half the globe. They originate at low latitudes on the margins of the subtropical high-pressure cells, and their constancy of direction and speed (about 7 m s-1) is remarkable. Trade winds, like the westerlies, are strongest during the winter half-year, which suggests they are both controlled by the same fundamental mechanism.
The two trade wind systems tend to converge in the Equatorial Trough (of low pressure). Over the oceans, particularly the central Pacific, the convergence of these air streams is often pronounced and in this sector the term Intertropical Convergence Zone (ITCZ) is applicable. Generally, however, the convergence is discontinuous in space and time. Equatorward of the main belts of the trades over the eastern Pacific and eastern Atlantic are regions of light, variable winds, known traditionally as the doldrums and much feared in past centuries by the crews of sailing ships. Their seasonal extent varies considerably: from July to September they spread westward into the central Pacific while in the Atlantic they extend to the coast of Brazil. A third major doldrum zone is located in the Indian Ocean and western Pacific. In March-April it stretches 16,000 km from East Africa to 180° longitude and it is again very extensive during October-December.
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Блок 3
OCEAN STRUCTURE AND CIRCULATION
Lesson 1
Упражнение 1.
Прочитайте заголовок приводимого ниже текста. Подумайте, о чем в нем может идти речь. Приведите 10–15 слов, которые могут, с Вашей точки зрения, встретиться в тексте.
Прочитайте и переведите текст.
Ocean vertical structure
The oceans occupy 71 per cent of the earth's surface, with over 60 per cent of the global ocean area in the southern hemisphere. Three-quarters of the ocean area is between 3,000 and 6,000 m deep, whereas only 11 per cent of the land area exceeds 2,000 m altitude.
a Vertical
The major atmosphere-ocean interactive processes involve heat exchanges, evaporation, density changes and wind shear. The effect of these processes is to produce a major oceanic layering that is of great climatic significance:
1 At the ocean surface, winds produce a thermally mixed surface layer averaging a few tens of metres deep poleward of latitude 60°, 400 m at latitude 40° and 100-200 m at the equator.
2 Below the relatively warm mixed layer is the thermocline,
a layer in which temperature decreases and density increases (the pycnocline) markedly with depth. The thermocline layer, within which stable stratification tends to inhibit vertical mixing, acts as a barrier between the warmer surface water and the colder deep-layer water. In the open ocean between latitudes of 60° north and south the thermocline layer extends from depths of about 200 m to a maximum of 1,000 m (at the equator from about 200 to 800 m; at 40° latitude from about 400 to about 1,100 m). Poleward of 60° latitude, the colder deep-layer water approaches the surface. Within the thermocline layer, the location of the steepest temperature gradient is termed the permanent thermocline, which has a dynamically inhibiting effect in the ocean similar to that of a major inversion in the atmosphere. However, heat exchanges take place between the oceans and the atmosphere by turbulent mixing above the permanent thermocline, as well as by upwelling and down-welling involving deep-layer water.
During spring and summer in the mid-latitudes, accentuated surface heating leads to the development of a seasonal thermocline occurring at depths of 50 to 100 m. Surface cooling and wind mixing tend to destroy this layer in autumn and winter. 3 Below the thermocline layer is a deep layer of cold, dense water. Within this, water movements are mainly driven by density variations, commonly due to salinity differences (i.e. having a thermohaline mechanism).
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The ocean may be viewed as consisting of a large number of layers, the topmost subject to wind stress, the next layer down to frictional drag by the layer above, and so on; all layers being acted on by the Coriolis force. The surface water tends to be deflected to the right (in the northern hemisphere) by an angle averaging some 45 ° in the surface wind direction and to move at about 3 per cent of its velocity. This deflection increases with depth as the friction-driven velocity of the current decreases exponentially. On the equator, where there is no Coriolis force, the surface water moves in the same direction as the surface wind. This theoretical Ekman spiral was developed under assumptions of idealized ocean depth, wind constancy, uniform water viscosity and constant water pressure at a given depth. This is seldom the case in reality, and under most oceanic conditions the thickness of the wind-driven layer is about 100 to 200 m.
Упражнение 2.
Прочитайте следующие слова и определите их соответствия
в русском языке:
Hemisphere, thermocline, pycnocline, process, temperature, stratification, vertical, barrier, maximum, location, gradient, dynamically, upwelling, seasonal, exponentially, theory, spiral, idealize, constant, reality.
Упражнение 3.
Определите, к каким частям речи относятся следующие слова; напишите соответствующие английские сокращения для каждого из них (v., adv., n., adj., conj., part., prep., pron.):
Vertical, evaporation, as, with, which, within, colder, has, however, termed, occurring, mainly, thickness.
Упражнение 4.
В правой колонке найдите русские эквиваленты следующих английских словосочетаний:
| 1. heat exchange 2. vertical mixing 3. temperature gradient 4. water movement 5. density variation 6. wind stress 7. wind direction 8. ocean depth 9. surface layer | a. глубина океана b. движение воды c. направление ветра d. поверхностный слой e. температурный градиент f. теплообмен g. вертикальное перемешивание h. изменения плотности i. ветровое воздействие |
Упражнение 5.
Заполните, где это возможно, таблицу, вставив недостающие части речи.
| v. | n. | adj. | adv. |
| produce extend | significance variation | stable | dynamically relatively |
Упражнение 6.
Прочитайте следующие выражения:
206 km; 1-2 m/day; 30°C; 1700; 1,367; 2.68931.
Упражнение 7.
Вставьте соответствующий предлог и подберите определение к каждому слову :off about up away for down on out.
| 1. pass … 2. make … 3. bring … 4. clear … 5. cut … 6. do 7. fall 8. fill | a. выяснять b. продолжать c. расширять e. направляться f. снимать g. покидать h. вызывать i. сокращать |
Упражнение 8.
Прочитайте текст и найдите в нем ответы на следующие вопросы:
1. Какова средняя скорость апвеллинга?
2. От чего она зависит?
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3. Где расположен основной регион апвеллинга?
(Контрольное время – 7 минут)
Upwelling
In contrast with the currents on the west sides of the oceans, equatorward-flowing eastern currents acquire cyclonic vorticity, which is in opposition to the anticyclonic wind tendency, leading to relatively broad flows of low velocity. In addition, the deflection due to the Ekman effect causes the surface water to move westwards away from the coasts, leading to replacement by the upwelling of cold water from depths of 100-300 m. Average rates of upwelling are low (l-2m/day), being about the same as the offshore surface current velocities, with which they are balanced. The rate of upwelling therefore varies with the surface wind stress. As the latter is proportional to the square of the wind speed, small changes in wind velocity can lead to marked variations in rates of upwelling. Although the band of upwelling may be quite narrow (about 200 km wide for the Benguela Current), the Ekman effect spreads this cold water westwards. On the poleward margins of these cold-water coasts, the meridional swing of the wind belts imparts a strong seasonality to the upwelling, the California Current upwelling, being particularly well marked during the period March-July.
A major region of deep-water upwelling is along the west coast of South America, which is normally assisted by the offshore airflow associated with the large-scale convective Walker cell linking South-east Asia with the eastern South Pacific. Every 2-10 years or so this pressure difference is disturbed, producing an El Nino event with weakening trade winds and a pulse of warm surface water spreading eastwards over the South Pacific, raising average ocean-surface temperatures from about 24 to 30 °C. Coastal upwelting can also he caused by other less important mechanisms such as surface current divergence or the effect of the ocean bottom configuration.
Упражнение 9.
Выберите из текста Upwelling 10–15 основных, с точки зрения смысловой нагрузки, слов (ключевые слова). Определите, к каким частям речи они относятся.
Упражнение 10.
Переведите текст письменно. (Контрольное время – 30 минут)
El Nino
The ocean is a thin, spherical shell of fluid on a rotating sphere and, in addition to the waves seen on the ocean surface when the wind is blowing, there are other waves that have a large amplitude, not at the surface, but along the subsurface thermocline. Some are confined to the neighborhood of the equator where they travel exceptionally fast. Because of those waves, warm surface waters can be redistributed along the equator far more rapidly than is possible at higher latitudes, which is why large-scale changes in sea surface temperature patterns, associated with a horizontal redistribution of upper ocean water, occur more readily in the tropics than in higher latitudes. Such an occurrence that leads to high sea surface temperatures in the eastern tropical Pacific is known as El Nino. The interval between El Nino episodes, three years approximately, depends on the time it takes the waves to propagate across the basin and hence depends on the width of the Pacific.
EL NINO affects everyone, either directly because of its influence on climate and weather, or indirectly because of its influence on the global economy. The impact of this phenomenon can be: devastating floods in Ecuador and Peru, where a warming of the surface waters of the eastern tropical Pacific – the signature of El Nino – is associated with the disappearance of the usually abundant fish; disastrous droughts in the "maritime" continent of southeastern Asia and northern Australia; unusual weather patterns over North and South America; poor monsoons over India; and low rainfall over southeastern Africa.
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Упражнение 11.
Составьте 5 общих вопросов к тексту El Nino.
Упражнение 12.
(Парная работа) Ответьте на вопросы, составленные в упражнении 11.
Lesson 2
Упражнение 1.
Подумайте и приведите 10–15 слов, которые могут встретиться в тексте.
Прочитайте и переведите текст.
Ocean circulation
(1) General
Comparisons between the structure and dynamics of the oceans and the atmosphere have long been made, particularly in respect of their behaviour above the permanent thermocline and below the tropopause – their two most significant stabilizing boundaries. Within these two zones, fluid-like circulations are maintained by meridional thermal energy gradients, dominantly directed polewards, and acted upon by the Coriolis force. Prior to the last quarter of a century, oceanography was studied in a coarsely averaged spatial-temporal framework similar to that applied in classical climatology. At the present day, however, its similarities with modern meteorology are more marked. The major behavioural differences between the oceans and the atmosphere derive from the greater density and viscosity of ocean waters and the much greater frictional constraints placed on their global movement.
Macroscale characteristics of ocean dynamics that invite comparison with atmospheric features include the general circulation, major oceanic gyres (similar to atmospheric subtropical high-pressure cells), major jet-like streams such as sections of the Gulf Stream, large-scale areas of subsidence and uplift, the stabilizing layer of the permanent thermocline, boundary layer effects, frontal discontinuities created by temperature and density contrasts, and water mass ('mode water') regions.
Mesoscale characteristics inviting atmospheric analogues are oceanic cyclonic and anticyclonic eddies, current meanders, cast-off ring vortices, jet filaments, and circulations produced by irregularities in the North Equatorial Current.
(2) Macroscale
The most obvious feature of the surface oceanic circulation is the control exercised over it by the low-level planetary wind circulation, especially by the subtropical oceanic high-pressure circulations and the westerlies. The oceanic circulation also displays seasonal reversals of flow in the monsoonal regions of the northern Indian Ocean, off East Africa and off northern Australia. As water moves meridionally, the conservation of angular momentum implies changes in relative vorticity, with poleward-moving currents acquiring anticyclonic vorticity and equatorward-moving currents acquiring cyclonic vorticity.
The more or less symmetrical atmospheric subtropical high-pressure cells produce oceanic gyres with centres displaced towards the west sides of the oceans. The gyres in the southern hemisphere are more symmetrically located than those in the northern, due possibly to their connection with the powerful West Wind Drift. This results, for example, in the Brazil Current being not much stronger than the Benguela Current. The most powerful southern hemisphere current, the Agulhas, possesses nothing like the jet-like character of its northern counterparts.
Equatorward of the subtropical high-pressure cells, the persistent trade winds generate the broad North and South Equatorial Currents. On the western sides of the oceans, most of this water swings polewards with the airflow and thereafter increasingly comes under the influence of the Ekman deflection and of the anticyclonic vorticity effect. However, some water tends to pile up near the equator on the western sides of oceans, partly because here the Ekman effect is virtually absent, with little poleward deflection and no reverse current at depth. To this is added some of the water that is displaced northwards into the equatorial zone by the especially active subtropical high-pressure circulations of the southern hemisphere. This accumulated water flows back eastward down the hydraulic gradient as compensating narrow surface Equatorial Counter-Currents, unimpeded by the weak surface winds. Near the equator in the Pacific Ocean, upwelling raises the thermo-cline to only 50-100 m depth, and within this layer there exist thin, jet-like Equatorial Undercurrents flowing eastwards (under hydraulic gradients) at the considerable velocity of 1 to 1.5 m s '.
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As the circulations swing polewards around the western margins of the oceanic subtropical high-pressure cells, there is the tendency for water to pile up against the continents, giving, for example, an appreciably higher sea level in the Gulf of Mexico than that along the Atlantic coast of the United States. This accumulated water cannot escape by sinking because of its relatively high temperature and resulting vertical stability, and it consequently continues polewards in the dominant direction of surface airflow, augmented by the geostrophic force acting at right angles to the ocean surface slope. As a result of this movement, the current gains anti-cyclonic vorticity, which reinforces the similar tendency imparted by the winds, leading to relatively narrow currents of high velocity (for example, the Kuroshio, Brazil, Mozambique-Agulhas and, to a less-marked extent, the East Australian Current). In the North Atlantic, the configuration of the Caribbean Sea and Gulf of Mexico especially favours this pile-up of water, which is released polewards through the Florida Straits as the particularly narrow and fast Gulf Stream. These poleward currents are opposed both by their friction with the nearby continental margins and by energy losses due to turbulent diffusion, such as those accompanying the formation and cutting off of meanders in the Gulf Stream. These poleward western boundary currents (e.g. the Gulf Stream and the Kuroshio Current) are fast, deep and narrow (i.e. approximately 100 km wide and reaching surface velocities greater than 2 m s"1), contrasting with the slower, wider and more diffuse eastern boundary currents such as the Canary and California (i.e. approximately 1,000 km wide with surface velocities generally less than 0.25 m s"1). The northward-flowing Gulf Stream causes a heat flux of 1.2 × 10ls W, 75 per cent of which is lost to the atmosphere and 25 per cent in heating the Greenland-Norwegian Seas area.
On the poleward sides of the subtropical high-pressure cells, westerly currents dominate, and where they are unimpeded by land masses in the southern hemisphere they form the broad and swift West Wind Drift. This strong current, driven by unimpeded winds, occurs within the zone 50 to 65°S and is associated with a southward-sloping ocean surface generating a geostrophic force, which intensifies the flow. Within the West Wind Drift, the action of the Coriolis force produces a convergence zone at about 50°S marked by westerly submarine jet streams reaching velocities of 0.5 to 1 m s"1. In the northern hemisphere, a great deal of the eastward-moving current in the Atlantic swings northwards, leading to anomalously very high sea temperatures, and is compensated for by a southward flow of cold arctic water at depth. However, more than half of the water mass comprising the North Atlantic Current, and almost all that of the North Pacific Current, swings south around the east sides of the subtropical high-pressure cells, forming the Canary and California Currents. Their southern-hemisphere equivalents are the Benguela, Humboldt or Peru, and West Australian Currents.
(3) Mesoscale
Mesoscale eddies and rings in the upper ocean are generated by a number of mechanisms, sometimes by atmospheric convergence or divergence or by the casting off of vortices by jet-like currents such as the Gulf Stream. These vortices are generated by the transfer of warm water from low to high latitudes. Oceanographic eddies occur on the scale of 50–400 km diameter and are analogous to atmospheric low- and high-pressure systems. Ocean mesoscale systems are much smaller than atmospheric depressions (which average about 1,000 km diameter), travel much slower (a few kilometres per day, compared with about 1,000 km per day for a depression) and persist from one to several months (compared with a depression life of about a week). Their maximum rotational velocities occur at a depth of about 150 m, but the vortex circulation may be felt to depths of several thousands of metres. Some eddies move parallel to the main flow direction, but many move irregularly equatorwards or polewards. In the North Atlantic, for example, this produces a 'synoptic-like' situation in which up to 50 per cent of the area may be occupied by mesoscale eddies. Cyclonic rings are commonly three times as numerous as anticyclonic eddies, having
a maximum rotational velocity of about 1.5 m s 1.
Упражнение 2.
Ответьте на следующие вопросы:
1. В чем причина основных различий в поведении между океаном и атмосферой?
2. Какие общие макро- и мезомасштабные детали характерны для циркуляции атмосферы и океана?
3. В чем заключается эффект Экмана?
4. Почему уровень моря в Мексиканском заливе выше, чем у Атлантического побережья США?
5. Какой наклон в южном полушарии имеет поверхность океана?
Упражнение 3.
Найдите в тексте термины, соответствующие следующим выражениям.
| especially | apparent | because of | yet |
| like | show | own | close |
| originate | shift | wide |
Упражнение 4.
Словам в левой колонке подберите антонимы в правой колонке.
| 1. long 2. below 3. similarity 4. most 5. stronger 6. sink 7. shallow 8. move | a. difference b. weaker c. raise e stay f. short g. deep h. above i. least |
Упражнение 5.
Переведите следующие слова на русский язык.
| however | for example | like | towards | between |
| such as | consequently | within | about | over |
| dominantly | some | almost | commonly | also |
Упражнение 6.
Из слов в правой и левой колонке образуйте цепочки существительных:
ocean layer
energy mass
boundary dynamics
density meander
water contrast
ring gradient
trade vortex
current wind
Упражнение 7.
Образуйте причастия 1 и 2 рода из следующих глаголов. Найдите примеры таких причастий в тексте из упражнения 1.
Derive, invite, display, imply, produce, posses, generate, tend, raise.
Упражнение 8.
Прочитайте текст. (Контрольное время –??? минут)
Deep ocean circulation
Whereas above the permanent thermocline the ocean circulation is mainly wind driven, the deep ocean circulation is powered by density gradients due to salinity and temperature differences. These differences are mostly produced by surface processes, which feed cold, saline water to the deep ocean basins in compensation for the deep water delivered to the surface by upwelling. Although upwelling occurs chiefly in narrow coastal locations, subsidence takes place largely in two broad ocean regions – the northern North Atlantic and the Antarctic Weddell Sea.
In the North Atlantic, particularly in winter, heating and evaporation produce warm, saline water which flows northwards both in the near-surface (Gulf Stream-North Atlantic Current and at intermediate depths of around 800 m. In the Norwegian and Greenland Seas, its density is enhanced by further evaporation due to high winds, by the formation of sea ice, which expells brine during ice growth, and by cooling. Exposed to evaporation and to the chill high-latitude air masses, the surface water cools from about 10 to 2°C, releasing immense amounts of heat to the atmosphere, supplementing solar insolation there by some 25-30 per cent and heating Western Europe. The resulting dense high-latitude water, equivalent in volume to about twenty times the combined discharge of all the world's rivers, sinks to the bottom of the North Atlantic and fuels a southward-flowing density (thermohaline) current, which forms part of a global deep-water conveyor belt. This broad, slow and diffuse How, occurring at depths of greater than 1,500 m, is augmented in the South Atlantic/circum-Antarctic/ Weddell Sea region by more cold, saline, dense subsiding water. The conveyor belt then flows eastwards under the Coriolis influence, turning north into the Indian and, especially, the Pacific Ocean. The time taken for the conveyor belt circulation to move from the North Atlantic to the North Pacific has been estimated at 500-1,000 years. In the Pacific and Indian Oceans, a decrease of salinity due to water mixing causes the conveyor belt to rise and to form a less deep return flow to the Atlantic, the whole global circulation occupying some 1,500 years or so. An important aspect of this conveyor belt flow is that the western Pacific Ocean contains a deep source of warm summer water (29°C). This heat differential with the eastern Pacific assists the high phase Walker circulation.
The thermal significance of the conveyor belt implies that any change in it may promote climatic changes, which may be apparent at time scales of several hundred or thousand years. It has been suggested, however, that any impediment to the rise of deep conveyor belt water might cause ocean surface temperatures to drop by 6°C within 30 years at latitudes of 60°N. Changes to the conveyor belt circulation might be caused by lowering the salinity of the surface water of the North Atlantic by increased precipitation, ice melting, or fresh water inflow. However, the complex mechanisms and consequences of the deep ocean conveyor belt are still only imperfectly understood.
Упражнение 9.
Ответьте на следующие вопросы, исходя из информации
в тексте:
1. Что является основными факторами, обусловливающими глубоководную циркуляцию в океане?
2. Каковы основные крупномасштабные особенности глубоководной циркуляции в океане?
3. Чем могут быть вызваны изменения в глубоководной циркуляции, и к каким последствиям они могут привести?
Упражнение 10.
Выпишите 10 ключевых слов из текста в упражнении 8.
Упражнение 11.
Письменно переведите текст. (Контрольное время – 30 минут)
The Southern Oscillation
The locations of the furnaces, the convective zones of rising air and low surface pressures, are determined by temperature patterns at Earth's surface. The air ascends where surface temperatures have maxima. The seasonal north-south migrations of the convective zones therefore tend to keep those zones in the summer hemisphere. Over Africa and South America the zones of heavy rainfall are difficult to dislodge from the continents because surface temperatures can attain higher values on land than over the oceans. The maritime continent of southeastern Asia is an entirely different matter because its eastern boundary coincides with that of the pool of warm water that covers the western tropical Pacific. Should this pool expand eastward, so would the region of rising air and heavy rainfall, which is exactly what happens interannually during El Nino. On such occasions, the eastern tropical Pacific experiences an increase in sea surface temperatures and in rainfall, a decrease in surface pressure, and a relaxation of the trade winds. Because of this eastward shift, the tropical regions west of the date line, including India and southeastern Africa, experience decreases in rainfall.
In the same way that the seasonal cycle is an oscillation between winter and summer, so the Southern Oscillation is a fluctuation between El Nino and a complementary state, which has been given the apposite name La Nina. Whereas the seasonal cycle is forced by regular variations in the intensity of sunlight, the Southern Oscillation corresponds to a natural mode of oscillation of the coupled ocean and atmosphere and is literally the music of our spheres (the atmosphere and hydrosphere).
Блок 4
WATER RESOURCES
Lesson 1
Упражнение 1.
Прочитайте и переведите следующий текст.
Water – Facts and Figures
Hydrology is a science dealing with the waters of the earth, their occurrence, distribution and circulation, their chemical and physical properties and their interaction with the environment. In this context, water is viewed in the same way as soil, vegetation, climate or rock, as an element of the landscape to be investigated and ultimately understood by means of rigorous scientific quantification and analysis. Water, the subject of hydrology, is both commonplace and unique. It is found everywhere in the earth's ecosystem and taken for granted in much of the developed world. It is, however, the only naturally occurring inorganic liquid and is the only chemical compound that occurs in normal conditions as a solid, a liquid and a gas. Its distribution over the globe is amazingly uneven.
Water plays a fundamental part in the distribution of chemicals through its central role in many chemical reactions, the transport of dissolved chemicals and the erosion and deposition of sediments. Its gaseous form, water vapour, is the principal greenhouse gas in the earth's atmosphere, an order of magnitude greater than CO2, which is the second most important greenhouse gas.
About 97% occurs as saline water in the seas and oceans. Only the remaining 3% is fresh water and of this, considerably more than one half is locked up in ice sheets and glaciers and another substantial volume occurs as virtually immobile deep groundwater. The really mobile fresh water, which contributes frequently and actively to rainfall, evaporation and streamflow, thus represents only about 0.3% of the global total. These estimated values of global water storage must be treated with caution because of the difficulties of monitoring and exact quantification at the macroscale. For example, the volumes of the ocean basins and of the major ice sheets depend upon sea bed and sub-ice topography which have only recently been mapped with reasonable accuracy. Reserves of deep groundwater are difficult to assess and estimates are periodically revised, usually upwards, like those of fossil fuels. Shallow groundwater storage is more accessible and mostly easier to estimate, although the proportion of usable non-saline water is still far from certain. Atmospheric water vapour content is normally monitored either by radio-sonde balloons released daily from just 1500 global locations or from ultra-red spectrometers in weather satellites. Unfortunately, due to the presence of clouds, IR spectrometry is more difficult to interpret for the air layers closest to the earth's surface, where water vapour values are the highest.
In the past, hydrologists focused their attention on the relatively small amount of fresh water occurring either as rivers, lakes, soil water and shallow groundwater, or in the vegetation cover and the atmosphere. Increasingly, however, it is recognized that the oceans play a dominant role in the global water and energy budgets and that large-scale perturbations of the hydrological system may result from changes in sea surface temperature, such as those associated with El Nino, or from modifications of the thermo-haline ocean circulation which may result from the increasingly rapid break-up of major ice sheets in both the northern and southern hemispheres. It is also important to recognize that the small volume of mobile fresh water is itself distributed unevenly in both space and time. Wetland and prairie, forest and scrub, snowfield and desert, each exhibits different regimes of precipitation, evaporation and streamflow, each offers different challenges of understanding for the hydrologist and of water management for the planner and engineer, and each poses different benefits and threats to human life and livelihood as between the developed and the developing world.
Упражнение 2.
Ответьте на вопросы:
1. What does hydrology deal with?
2. Where is water found on the planet?
3. What is unique about water as a chemical compound?
4. What is the principal greenhouse gas on the earth?
5. How much saline and fresh water is there on our planet?
6. Why should global water storage values be treated carefully?
7. What has been mapped only recently?
8. Which water reserves are easier to be estimated? Which are more difficult?
9. How is water vapour content monitored?
10. What water did hydrologists study in the past?
11. What plays the main role in the global water and energy budgets?
12. How unevenly is water distributed?
Упражнение 3.
Соедините слова в колонках A и В.
| A. | В. |
| sea | fuel |
| ice | gas |
| water | flow |
| stream | water |
| greenhouse | management |
| ocean | bed |
| water | sheet |
| earth's | storage |
| fossil | surface |
| soil | basin |
Упражнение 4.
Переведите следующие выражения на английский язык:
Посредством (при помощи), оставшийся, неравномерный, относительно, принимать как должное, быстрый, зависеть от, или…или.., как... так и..., из-за (2), однако, хотя, все еще, между, следовательно (2), близко, в основном, к сожалению, значительно, тот же самый, свойство, встречаться, представлять, оценка (2).
Упражнение 5.
Образуйте причастия 1 и 2 рода из следующих глаголов. Найдите примеры таких причастий в тексте из упражнения 1.
Estimate, develop, investigate, depend, remain, grant, understand, show, focus, recognize, associate, use, occur, find.
Упражнение 6.
Образуйте наречия из следующих слов:
Increase, consider, main, substantial, day, period, frequent, globe, ultimate, nature, science, amaze, virtual, large.
Упражнение 7.
Образуйте соответствующие части речи из приведенных
в скобках слов:
Glaciers store water over (relate) long timescales compared to rivers and lakes -hundreds to a few thousands of years. Ice sheets store water for even (long) - ten thousands of years. But the shorter glacier timescales are (compare) to human timescales, so people notice how glaciers change, and these changes have obvious impacts on the human environment. Many river systems depend on glacier melt, which (maintain) the water supply through the summer. As glaciers shrink, so does the (freeze) water supply they store. This is one of the reasons why it is important to measure how and understand why glaciers change over time.
Glacier meltwater (event) makes its way to the ocean, where it can affect global sea level. As terrestrial ice masses grow, sea level (fall); and as masses shrink, sea level (rise). At the last glacial maximum, about 18,000 years ago, the growth of ice sheets and glaciers (cause) sea level to lower by about 120 meters. Most of that change (be) due to the formation of large ice sheets in northern North America and Europe, but mountain glaciers, too, had their role.
Упражнение 8.
Поставьте глаголы в скобках в форму страдательного залога:
Approximately 97% of the fresh water available in the world is underground. Wells provide groundwater for individual domestic needs, communities, cities, industry, crop irrigation and agriculture. Some wells tap hot water, or geothermal resources. In other cases, groundwater (use) solely for its cooling capabilities. Some wells (dig) just to study water quality or quantity: these (call) monitoring or observation wells.
Regardless of its purpose, a well (define) as an artificial hole in a land surface created to access a liquid. It normally has a small diameter, typically less than 3 meters and usually (measure) in centimeters. Wells may (construct) to seek water, oil or natural gas.
Упражнение 9.
Составьте вопросы к тексту из упражнения 8.
1. Where/ fresh water/ available?
2. What/ groundwater/ provided/ for?
3. Wells/ tap/ solely/ cold water?
4. What kind of wells/ dug/study/water quality or quantity?
5. How/ a well/ defined?
6. How big/ its diameter?
7. Why/ wells/ constructed?
Упражнение 10.
В приведенном ниже тексте используйте следующие слова: can, providing, however, satellites,due to, cooling, atmospheric, causes, boarded, observers.
Snow and ice account for just over 75% of the Earth's freshwater, although most of this is held as ice in Antarctica and Greenland, with
a residence time of the order of 10, 000 years. Snow has a great hydrological importance. It has a … effect on climate by increasing the albedo and modifying the surface radiation balance and the near-surface air temperature, and it … a great amount of energy to be expended on melting. Seasonal snow cover changes are known to affect global … circulation, and may have an important role influencing climatic change. In arid and semi-arid areas … by high mountains, including the semi-arid western United States, northern India and Iran, snowmelt is an important seasonal source of water. The presence of snow on the ground is important … disruption of travel and commerce, and seasonal flood risk may be increased by snowmelt. In addition to … a store of water, snow cover can serve as protective insulation for soil and crops through the winter. Information on the spatial distribution of snow was traditionally based on reports from … at meteorological stations. But it is difficult to gain a broad picture of the areal extent of snow cover from such local observations. Due to its high albedo, snow cover can be readily distinguished from snow-free ground using visible radiation reflectance. Remote sensing, from aircraft or … enables the rapid mapping of the extent of snow cover over large areas. It is,…, often difficult to distinguish snow from cloud cover using visible reflectance alone, without repeated photography over time to filter out the variable cloud pattern. This … be overcome by the use of "passive" microwave radiation emitted naturally by the Earth's surface. This can penetrate cloud cover and allow the mapping of snow extent unobstructed by weather effects. However, passive microwave data have a low spatial resolution of several tens of kilometers.
Lesson 2
Упражнение 1.
Прочитайте слова и словосочетания и попробуйте догадаться, о чем пойдет речь в следующем тексте:
Water supply, fresh water, human use, usable supply, natural purification, groundwater, surface water, precipitation, runoff.
Упражнение 2.
Прочитайте и переведите текст:
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