Energy transfer within the earth-atmosphere system

Lesson 2

Length of day

The length of daylight also affects the amount of radiation that is received. Obviously, the longer the time that the sun shines the greater is the quantity of radiation that a given portion of the earth will receive. At the equator; for example, the day length is close to 12 hours in all months, whereas at the poles it varies between 0 and 24 hours from winter (polar night) to summer. The polar regions receive their maximum amounts of solar radiation during their summer solstices, which is the period of continuous day. The amount received during the December solstice in the southern hemi­sphere is theoretically greater than that received by the northern hemisphere during the June solstice, due to the previously mentioned elliptical path of the earth around the sun. The equator has two radiation maxima at the equinoxes and two minima at the solstices, due to the apparent passage of the sun during its double annual move­ment between the northern and southern hemi­spheres.

Упражнение 11.

Составьте 5 общих вопросов к тексту Length of day.

Упражнение 12.

(Парная работа) Ответьте на вопросы, составленные в упражнении 11.

Упражнение 1.

Подумайте и приведите 10–15 слов, которые могут встретиться в тексте.

Прочитайте и переведите текст.

The distribution of solar radiation is often described as if it were all available at the earth's surface. This is, of course, an unreal view because of the effect of the atmosphere on energy transfer. Heat energy can be transferred by the three following mechanisms:

1 Radiation: Electromagnetic waves transfer energy (both heat and light) between two bodies, without the necessary aid of an intervening mate­rial medium, at a speed of 300 × 10⁶ m s^-1 (i.e. the speed of light). This is so with solar energy through space, whereas the earth's atmosphere allows the passage of radiation only at certain wavelengths and restricts that at others.

Radiation entering the atmosphere may be absorbed by atmospheric gases in certain wave­lengths but most short­wave radiation is transmitted without absorption. Scattering occurs if the direction of a photon of radiation is changed by interaction with atmos­pheric gases and aerosols. Two types of scatter­ing are distinguished. For gas molecules smaller than the radiation wavelength (λ) Rayleigh scat­tering occurs in all directions and is proportional to (1/λ⁴). As a result, the scattering of blue light (λ@0.4µm) is an order of magnitude (i.e.×10) greater than that of red light (λ @ 0.7 µm), thus creating the daytime blue sky. However, when water droplets or aerosol particles, with similar sizes (0.1-0.5 µm radius) to the radiation wave­length, are present, most of the light is scattered forward. This Mie scattering gives the greyish appearance of polluted atmospheres.

Within a cloud, or between low clouds and a snow-covered surface, radiation undergoes multiple scattering. In the latter case, the 'white out' conditions typical of polar regions in summer (and mid-latitude snowstorms) are expe­rienced, when surface features and the horizon become indistinguishable.

2 Conduction: By this mechanism, the heat passes through a substance from point to point by means of the transfer of adjacent molecular motions. Since air is a poor conductor, this type of heat transfer can be virtually neglected in the atmosphere, but it is important in the ground.

3 Convection: This occurs in fluids (including gases), which are able to circulate internally and distribute heated parts of the mass. The low viscosity of air and its consequent ease or motion makes this the chief method of atmospheric heat transfer. It should be noted that forced convec­tion (mechanical turbulence) occurs due to the development of eddies as air flows over uneven surfaces, even when there is no surface heating to set up free (thermal) convection.

Convection transfers energy in two forms. The first is the sensible heat content of the air (called enthalpy by physicists), which is transferred directly by the rising and mixing of warmed air. It is defined as c_pT, where T is the temperature and c_p (= 1,004 J kg^-1 K^-1) is the specific heat at constant pressure (the heat absorbed by unit mass for unit tempera­ture increase). Sensible heat is also transferred by conduction. The second form of energy transfer by convection is indirect, involving latent heat. Here, there is a phase change but no temperature change. Whenever water is converted into water vapour by evaporation (or boiling), heat is required. This is referred to as the latent heat of vaporiza­tion (L). At 0 °C, L is 2.50 x 10⁶ J kg^-1 of water. More generally,

where T is in °C. When water condenses in the atmosphere, the same amount of latent heat is given off as is used for evaporation at the same temperature. Similarly, for melting ice at 0 °C, the latent heat of fusion is required, which is 0.335 × 10⁶ J kg^-1. If ice evaporates without melting, the latent heat of this sublimation process is 2.83 × 10⁶ J kg^-1 at
0 °C (i.e. the sum of the latent heats of melting and vaporization). In all of these phase changes of water there is an energy transfer.

Упражнение 2.

Найдите в тексте термины, соответствующие следующим выражениям.

limit (v)	indiscernible	pierce	matter
look (n)	transfer (v)	inner	incoming (pres.) p)
common	for (conj)	rough

Упражнение 3.

Словам в левой колонке подберите антонимы в правой колонке.

1. smaller 2 poor 3. free 4. directly 5. same 6. necessary 7. may 8. latter

a. former b. optional c. different e greater f. should g. forced h. good i. indirectly

Упражнение 4.

Переведите следующие слова на русский язык.

Without whenever so by both … and …

by means of uneven forward most of smaller than

more generally similarly internally or as a result

Упражнение 5.

Из слов в правой и левой колонке образуйте цепочки существительных.

heat change

energy feature

radiation development

water interaction

surface energy

phase transfer

eddy droplet

gas wavelength

Упражнение 6.

Образуйте причастия 1 и 2 рода из следующих глаголов. Найдите примеры таких причастий в тексте из упражнения 1.

Restrict, occur, undergo, circulate, distribute, flow, transfer, condense.

Упражнение 7.

Прочитайте текст. (Контрольное время – 5 минут)

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