Головна

Solar radiation

  1. Mass extinctions and adaptive radiation.
  2. SOLAR ENERGY
  3. SOLAR POWERED CARS
  4. Text 9. Scientists use windows to trap solar energy

The prime source of the energy injected into our atmosphere is the sun, which is continually shedding part of its mass by radiating waves of electromagnetic energy and high-energy particles into space. This constant emission is important because it represents in the long run almost all the energy available to the earth (except for a small amount emanating from the radioactive decay of earth minerals). The amount of energy received by the earth, assuming for the moment that there is no interference from the atmosphere, is affected by four factors: solar output, the sun-earth distance, the altitude of the sun, and day length.

1 Solar output

Solar energy, which originates from nuclear reactions within the sun's hot core (16 * 106 K), is transmitted to the sun's surface by radiation and hydrogen convection. Visible solar radiation (light) comes from a 'cool' (~ 6,000 K) outer surface layer called the photosphere. Temperatures rise again in the outer chromosphere (10,000 K) and corona (106 K), which is continually expanding into space. The outflowing hot gases (plasma) from the sun, referred to as the solar wind (with a speed of 1.5 * 106 km hr-1), Interact with the earth's magnetic field and upper atmosphere. The earth intercepts both the normal electromagnetic radiation and energetic particles emitted by the sun during solar flares.

The sun behaves virtually as a black body, meaning that it both absorbs all energy received and in turn radiates energy at the maximum rate possible for a given temperature. The energy emitted at a particular wavelength by a perfect radiator of given temperature is described by
a relationship due to Max Planck. The total energy emitted by a black body is found by integration of Planck's equation, known as Stefan's Law:

F = Бt4

where б = 5.67 * 10-8 W m-2 K-2 (The Stefan-Boltzmann constant), i.e. the energy emitted (F) is proportional to the fourth power of the absolute temperature of the body (T).

The total solar output to space, assuming a temperature of 5,760 K for the sun, is 3.84 * 1026 W, but only a tiny fraction of this is intercepted by the earth, because the energy received is inversely proportional to the square of the solar distance (150 million km).

The energy received at the top of the atmosphere on a surface perpendicular to the solar beam for mean solar distance is termed the solar constant. The most recent satellite measurements indicate a value of about 1,368 Wm-2. For solar radiation, 8 per cent is ultraviolet and shorter wavelength emission, 39 per cent visible light (0.4-0.7 µm) and 53 per cent near-infrared (> 0.7 µm). The mean temperature of the earth's surface is about 288 K (15 ° C) and of the atmosphere about 250 K (-23 ° C). Gases do not behave as black bodies, the absorption bands in the atmosphere cause its emission to be much less than that from an equivalent black body. The wavelength of maximum emission varies inversely with the absolute temperature of the radiating body.

Thus solar radiation is very intense and is mainly short-wave between about 0.2 and 4.0 ?m, with a maximum (per unit wavelength) at 0.5 ?m, whereas the much weaker 'terrestrial radiation has a peak intensity at about 10 ?m and a range of about 4 to 100 ?m (1 ?m = 1 micrometre = 10-6 m).

Satellite data show that the solar constant undergoes small periodic variations of about 0.1 per cent, related to sunspot activity. Sunspots are dark (i.e. cooler) areas visible on the sun's surface. Their number and positions change in a regular manner, known as the sunspot cycles. These cycles have wavelengths averaging 11 years (varying in length between 8 and 13 years), the 22-year (Hale) magnetic cycle, much less importantly 37.2 years (18.6 years - the luni-solar oscillation) and possibly 80-90 years. Between the thirteenth and eighteenth centuries, sunspot activity was generally low, except for the periods AD 1350-1400, and 1600-1645. Output within the ultraviolet part of the spectrum shows considerable variability, with up to twenty times more ultraviolet radiation emitted at certain wavelengths during a sunspot maximum than during a sunspot minimum. The relation between sunspot activity and terrestrial temperatures is a matter of some dispute. However, some authorities believe that prolonged time- spans of sunspot minima (e.g. AD 1645-1705, the Maunder Minimum) and maxima (e.g. 1895-1940 and post 1970) can produce significant global cooling and warming, respectively.

Shorter-term relationships are more difficult to support, but mean annual temperatures have been correlated with the combined 10-11 and 18.6-year solar cycles. Satellite measurements during the 1980s, the latest solar cycle, show a small decrease in solar output as sunspot number approaches its minimum, and a subsequent recovery. Although sunspot areas are cool spots, they are surrounded by bright areas of activity known as faculae, which have higher temperatures; the net effect is for solar output to vary in parallel with the number of sunspots. Thus, the solar 'irradiance' decreases by about 1.5 Wm-2 from sunspot maximum to minimum. In the long term, assuming that the earth behaves as a black body, a long-continued difference of 2 per cent in the solar constant could change the effective mean temperature of the earth's surface by as much as 1.2 ° C; however, the observed fluctuations of about 0.1 per cent would change the mean global temperature by ?0.06 ° C, based on calculations of radiative equilibrium.

Вправа 2.

Прочитайте наступні слова і визначте їх відповідності
в Російській мові:

Radiation, mass, electromagnetic, moment, solar, photosphere, chromosphere, corona, plasma, fraction, proportional, perpendicular, constant, ultraviolet, infrared, peak, intensity, periodical, regular, manner.

Вправа 3.

Знайдіть в тексті з вправи 1 слова з суфіксом ~ ly. Визначте, якими частинами мови вони є.

Вправа 4.

У правій колонці знайдіть російські еквіваленти наступних англійських словосполучень:

 1. in the long run2. the fourth power3. much less4. in a regular manner5. twenty times6. inversely proportional7. long-wave radiation8. near-infrared9. radioactive decay  a. назад пропорціональнийb. двадцять разc. ближній інфракраснийd. довгохвильова радіаціяe. радіоактивний распадf. четверта степеньg. в общемh. набагато меньшеi. регулярним чином

Вправа 5.

Заповніть таблицю, вставивши відсутні частини мови.

 v.  n.  adj.  adv.
 originate emit  radiation oscillation  particular  importantly respectively

Вправа 6.

Вставте в пропуски в тексті відповідні прийменники: at, with, of, to, by, throughout, between, in, per, through




ISBN 978-5м -86813-306-0 | Distance from the sun | Length of day | Energy transfer within the earth-atmosphere system | Effect of the atmosphere | Composition of the atmosphere | Variation with height | Variations with latitude and season | The layering of the atmosphere | Ozone layer reduction |

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