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The layering of the atmosphere
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The atmosphere can be divided conveniently into a number of rather well-marked horizontal layers, mainly on the basis of temperature. The evidence for this structure comes from regular rawinsonde (radar wind-sounding) balloons, radio-wave investigations, and, more recently, from rocket flights and satellite sounding systems. Broadly, the pattern consists of three relatively warm layers (near the surface; between 50 and 60 km; and above about 120 km) separated by two relatively cold layers (between 10 and 30 km; and 80-100 km).
1 Troposphere
The lowest layer of the atmosphere is called the troposphere. It is the zone where weather phenomena and atmospheric turbulence are most marked, and it contains 75 per cent of the total molecular or gaseous mass of the atmosphere and virtually all the water vapour and aerosols. Throughout this layer, there is a general decrease of temperature with height at a mean rate of about 6.5 °C/km. The decrease occurs because air is compressible and its density decreases with height,allowing rising air to expand and thereby cool. Additionally, the atmosphere is heated mainly by turbulent heat transfer from the surface, not by absorption of radiation. The troposphere is capped in most places by a temperature inversion level (i.e. a layer of relatively warm air above a colder one) and in others by a zone that is isothermal with height. The troposphere' thus remains to a large extent self-contained, because the inversion acts as a 'lid' that effectively limits convection. This inversion level or weather ceiling is called the tropopause. Its height is not constant in either space or time. It seems that the height of the tropopause at any point is correlated with sea level temperature and pressure, which are in turn related to the factors of latitude, season and daily changes in surface pressure. There are marked variations in the altitude of the tropopause with latitude, from about 16 km at the equator, where there is great heating and vertical convective turbulence, to only 8 km at the poles.
The meridional temperature gradients in the troposphere in summer and winter are roughly parallel, as are the tropopauses, and the strong lower mid-latitude temperature gradient in the troposphere is reflected in the tropopause breaks. In these zones, important interchanges can occur between the troposphere and stratosphere, and vice versa. Traces of water vapour probably penetrate into the stratosphere by this means, while dry, ozone-rich stratospheric air may be brought down into the mid- latitude troposphere. For example, above-average concentrations of ozone are observed in the rear of mid-latitude low-pressure systems, where the tropopause elevation tends to be low. Both facts are probably the result of stratospheric subsidence, which warms the lower stratosphere and causes downward transfer of the ozone.
2 Stratosphere
The second major atmospheric layer is the stratosphere, which extends upwards from the tropopause to about 50 km. Although the stratosphere contains much of the total atmospheric ozone (it reaches a peak density at approximately 22 km), the maximum temperatures associated with the absorption of the sun's ultraviolet radiation by ozone occur at the stratopause, where temperature may exceed 0 °C. The air density is much less here, so even limited absorption produces a large temperature increase. Temperatures increase fairly generally with height in summer, with the coldest air at the equatorial tropopause. In winter, the structure is more complex with very low temperatures, averaging -80 °C, at the equatorial tropopause, which is highest at this season. Similar low temperatures are found in the middle stratosphere at high latitudes, whereas over 50-60 °N there is a marked warm region with nearly isothermal conditions at about -45 to -50 °C. Marked seasonal changes of temperature affect the stratosphere. The cold 'polar night' winter stratosphere often undergoes dramatic sudden warmings associated with subsidence due to circulation changes in late winter or early spring, when temperatures at about 25 km may jump from -80 to -40 °C over a two-day period. The autumn cooling is a more gradual process. In the tropical stratosphere, there is a quasi-biennial (26-month) wind regime, with easterlies in the layer 18 to 30 km for 12 to 13 months, followed by westerlies for a similar period. The reversal begins first at high levels and takes approximately 12 months to descend from 30 to 18 km (10 to 60 mb).
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How far these events in the stratosphere are linked with temperature and circulation changes in the troposphere, remains a topic of meteorological research. Any interactions that do exist, however, are likely to be complex, otherwise they would already have become evident.
3 Mesosphere
Above the stratopause, average temperatures decrease to a minimum of about -133 °C (140 K) or around 90 km. This layer is commonly termed the mesosphere, although it must be noted that as yet there is no universal acceptance of terminology for the upper atmospheric layers. The layers between the tropopause and the lower thermosphere are now commonly referred to as the middle atmosphere, with the upper atmosphere designating the regions above about 100 km altitude. Above 80 km, temperatures again begin rising with height and this inversion is referred to as the 'mesopause', Molecular oxygen and ozone absorption bands contribute to heating around 85 km altitude. It is in this region that 'noctilucent clouds' are observed.over high latitudes in summer. Their presence appears to be due to meteoric dust particles, which act as ice crystal nuclei when traces of water vapour are carried upwards by high-level convection caused by the vertical decrease of temperature in the mesosphere. However, their formation is also thought to be related to the production of water vapour through the oxidation of atmospheric methane, since apparently they were not observed prior to the Industrial Revolution.
Pressure is very low in the mesosphere, decreasing from about 1 mb at 50 km to 0.01 mb at 90 km.
4 Thermosphere
Above the mesopause, atmospheric densities are extremely low, although the tenuous atmosphere still effects drag on space vehicles above 250 km. The lower portion of the thermosphere is composed mainly of nitrogen (N2) and oxygen in molecular (02) and atomic (O), forms, whereas above 200 km atomic oxygen predominates over nitrogen.(N2 and N). Temperatures rise with height, owing to the absorption of extreme ultraviolet radiation (0.125-0.205 м m) by molecular and atomic oxygen, probably approaching 800-1,200 K at 350 km, but these temperatures are essentially theoretical. For example, artificial satellites do not acquire such temperatures because of the rarefied air. 'Temperatures' in the upper thermosphere and exosphere undergo wide diurnal and seasonal variations. They are higher by day and are also higher during a sunspot maximum, although the changes are only represented in varying velocities of the sparse air molecules.
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Above 100 km, the atmosphere is increasingly affected by cosmic radiation, solar X-rays and ultra violet radiation, which cause ionization, or electrical charging, by separating negatively charged electrons from neutral oxygen atoms and nitrogen molecules, leaving the atom or molecule with a net positive charge (an ion). The Aurora Borealis and Aurora Australis are produced by the penetration of ionizing particles through the atmosphere from about 300 km to 80 km, particularly in zones about 10-20 ° latitude from the earth's magnetic poles. On occasion, however, the aurorae may appear at heights up to 1,000 km, demonstrating the immense extension of a rarefied atmosphere. The term ionosphere is commonly applied to the layers above 80 km.
5 Exosphere and magnetosphere
The base of the exosphere is between about 500 km and 750 km. Here atoms of oxygen, hydrogen and helium (about 1 per cent of which are ionized) form the tenuous atmosphere, and the gas laws (see B, this chapter) cease to be valid. Neutral helium and hydrogen atoms, which have low atomic weights, can escape into space since the chance of molecular collisions deflecting them downwards becomes less with increasing height. Hydrogen is replaced by the breakdown of water vapour and methane (CH4) near the mesopause, while helium is produced by the action of cosmic radiation on nitrogen and from the slow but steady breakdown of radioactive elements in the earth's crust.
Ionized particles increase in frequency through the exosphere and, beyond about 200 km, in the magnetosphere there are only electrons (negative) and protons (positive) derived from the solar wind - a plasma of electrically conducting gas.
Упражнение 2.
Ответьте на следующие вопросы:
1. Какой слой атмосферы является самым нижним?
2. Как в тропосфере температура изменяется с высотой?
3. Какую часть всей массы атмосферы включает тропосфера?
4. С чем связан максимум температуры в стратосфере?
5. Как меняется температура в стратосфере?
6. Какой слой атмосферы находиться над стратосферой?
7. К какому слою относится термин ионосфера?
8. На какой высоте располагается экзосфера?
9. Между какими частями атмосферы располагаются тропопауза, стратопауза и мезопауза?
Упражнение 3.
Найдите в тексте термины, соответствующие следующим выражениям.
| prevail | for instant | result in | man-made |
| actually | be exposed | notable | rare |
| warming | probably | changes | |
| on the contrary | meanwhile | involve |
Упражнение 4.
Добавьте одно или более слов в каждую группу.
| troposphere | low | divide |
| thermosphere | great | expand |
| exosphere | cool | remain |
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Упражнение 5.
Переведите следующие слова на русский язык.
| throughout | roughly | since | beyond | mainly |
| thereby | often | still | fairly | thus |
| additionally | otherwise | while | generally | in turn |
Упражнение 6.
Из слов в правой и левой колонке образуйте цепочки существительных:
rocket transfer
temperature regime
weather inversion
heat molecule
tropopause flight
wind atom
air phenomena
helium elevation
Упражнение 7.
Образуйте причастия 1 и 2 рода от следующих глаголов:
Come, consist, separate, occur, expend, remain, act, penetrate, warm.
Упражнение 8.
Прочитайте следующие выражения:
6.5º C/km, 12 moths, 140 K, 60 mb, 0.125 µm.
Упражнение 9.
Вставьте в пропуски в тексте подходящие предлоги:
by, on,of, for, to, in, from, about, by, over, due to.
Carbon dioxide
The major reservoirs … carbon are … limestone sediments and fossil fuels … land and … the world oceans. The atmosphere contains … 750×1012 kg … carbon, corresponding … a CO2 concentration … 358 ppm. The major fluxes … atmospheric carbon dioxide are a result … solution/dissolution … the ocean and decomposition … biota. The average time … CO2 molecule to be dissolved … the ocean or taken up … plants is about four years. Photosynthetic activity leading … primary production … land involves 50×1012 kg … carbon annually, representing 7 percent … atmospheric carbon; this accounts … the 14 ppm annual oscillation … CO2 observed … the northern hemisphere …its extensive land biosphere.
Упражнение 11.
Переведите текст письменно. (Контрольное время – 30 минут)
Ozone layer reduction
Ozone (03) is distributed very unevenly with height and latitude as a result of the complex photochemistry involved in its production. Since the late 1970s, dramatic declines in springtime total ozone have been detected over high southern latitudes. The normal increase in stratospheric ozone associated with increasing solar radiation in spring apparently failed to develop. Observations in Antarctica show a decrease in total ozone in September-October from 320 Dobson units (10-3 cm at standard atmospheric temperature and pressure) in the 1960s to around 100 in the 1990s. The results from one specific location illustrate the presence of an 'ozone hole' over the south polar region. Similar reductions are also evident in the Arctic and at lower latitudes. Between 1979 and 1986, there was a 30 per cent decrease in ozone at 30-40 km altitude between latitudes 20 and 50 °N and S; along with this there has been an increase in ozone in the lowest 10 km as a result of anthropogenic activities. These changes in the vertical distribution of ozone concentration are likely to lead to changes in atmospheric heating, with implications for future climate trends. The global mean column total decreased from 306 Dobson units for 1964-80 to 297 for 1984-93. The decline over the last 25 years has exceeded 7 per cent in middle and high latitudes.
The effects of reduced stratospheric ozone are particularly important for their potential biological damage to living cells and human skin. It is estimated that a 1 per cent reduction in total ozone will increase ultraviolet-B radiation by 2 per cent, for example, and ultraviolet radiation at 0.30 м m is a thousand times more damaging for the skin than at 0.33 м m. The ozone decrease would also be greater in higher latitudes. However, it should be noted that the mean latitudinal and altitudinal gradients of UV-B radiation imply that the effects of a 2 per cent UV-B increase in mid-latitudes could be offset by moving poleward 20 km or 100 m lower in altitude! Recent polar observations suggest more dramatic changes. Stratospheric ozone totals in 1990 over Palmer Station, Antarctica (65 °S), were found to have maintained low levels from September until early December, instead of recovering in November. Hence, the altitude of the sun was higher and the incoming radiation much greater than in previous years, especially at wavelengths <= 0.30 мm. It remains, however, to determine the specific effects of increased UV radiation on marine biota, for instance.
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Lesson 3
Упражнение 1.
Прочитайте и переведите текст.
The general circulation
The observed patterns of wind and pressure prompt consideration of the mechanisms maintaining the general circulation of the atmosphere – the large – scale patterns of wind and pressure that persist throughout the year or recur seasonally. Reference has already been made to one of the primary driving forces, the imbalance of radiation between lower and higher latitudes (see Figure 2.26), but it is also important to appreciate the significance of energy transfers in the atmosphere. Energy is continually undergoing changes of form, as shown schematically in Figure 6.17. Unequal heating of the earth and its atmosphere by solar radiation generates potential energy, some of which is converted into kinetic energy by the rising of warm air and the sinking of cold air. Ultimately, the kinetic energy of atmospheric motion on all scales is dissipated by friction end small-scale turbulent eddies (i.e. internal viscosity). In order to maintain the general circulation, the rate of generation of kinetic energy must obviously balance its rate of dissipation. These rates are estimated to be about 2 W m-2, which amounts to only 1 per cent of the average global solar radiation absorbed at the surface and in the atmosphere. In other words, the atmosphere is a highly inefficient heat engine.
A second controlling factor is the angular momentum of the earth and its atmosphere. This is the tendency for the earth's atmosphere to move, with the earth, around the axis of rotation. Angular momentum is proportional to the rate of spin (that is the angular velocity) and the square of the distance of the air parcel from the axis of rotation. With a uniformly rotating earth and atmosphere, the total angular momentum must remain constant (in other words, there is a conservation of angular momentum). If, therefore, a large mass of air changes its position on the earth's surface such that its distance from the axis of rotation also changes, then its angular velocity must change in a manner so as to allow the angular momentum to remain constant. Naturally, absolute angular momentum is high at the equator and decreases with latitude to become zero at the poles (that is, the axis of rotation), so air moving polewards tends to acquire progressively higher eastward velocities. For example, air travelling from 42 to 46° latitude and conserving its angular momentum would increase its speed relative to the earth's surface by 29 m s-1. This is the same principle that causes an ice skater to spin more violently when her arms are progressively drawn into the body. In practice, this increase of air-mass velocity is countered or masked by the other forces affecting air movement (particularly friction), but there is no doubt that many of the important features of the general atmospheric circulation result from this poleward transfer of angular momentum.
The necessity for a poleward momentum transport is readily appreciated in terms of the maintenance of the mid-latitude westerlies. These winds continually impart westerly (eastward) relative momentum to the earth by friction, and it has been estimated that they would cease altogether due to this frictional dissipation of energy in little over
a week if their momentum were not continually replenished from elsewhere. In low latitudes, the extensive tropical easterlies are gaining westerly relative momentum by friction as a result of the earth rotating in a direction opposite to their flow, and this excess is transferred polewards with the maximum poleward transport occurring, significantly, in the vicinity of the mean subtropical jet stream at about 250 mb at 30°N and 30°S.
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Упражнение 2.
Прочитайте следующие слова и определите их соответствия
в русском языке:
energy, form, potential, kinetic, turbulent, circulation, generation, momentum, absolute, equator, progressively, principle, practice, mask, transport, tropical, subtropical.
Упражнение 3.
Заполните таблицу, образовав недостающие части речи.
| v. | n. | adj. | adv. |
| extend | conservation | relative | continually progresssively |
Упражнение 4.
В правой колонке найдите русские эквиваленты следующих английских словосочетаний из текста The general circulation:
| 1. driving force 2. unequal heating 3. angular velocity 4. jet stream 5. large-scale 6. same principle 7. violently 8. altogether 9. over a week 10. ultimately 11. therefore | a. тот же самый принцип b. в течение недели c. все вместе d. следовательно e. струйное течение f. неравномерное нагревание g. в основном h. угловая скорость i. крупномасштабный j. управляющая сила k. сильно |
Упражнение 5.
Составьте 5 вопросов к первому абзацу текста The general circulation.
Упражнение 6.
(Парная работа) Ответьте на вопросы в упражнении 6.
Упражнение 7.
Найдите подлежащее в каждом предложении второго абзаца текста The general circulation.
Упражнение 8.
Вставьте соответствующий предлог и подберите определение к каждому глаголу: about, down, off, into, up, in for.
| 1. break … 2. look … 3. pick … 4. leave … 5. go … 6. lead … 7. cut … 8. get … | a. начать b. распространяться c. перестать e сокращать f. исследовать g. расщеплять h. получать i. интересоваться |
Упражнение 9.
Прочитайте текст и найдите ответы на следующие вопросы:
1. От чего зависит вертикальные изменения давления с высотой?
2. Какой тип центров действия атмосферы преобладает в субтропических, субполярных и экваториальных зонах?
3. Какие ветра преобладают в тропической и умеренной зоне?
4. Какой тип циркуляции называют ячейкой Уокера?
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