Solar radiation outside atmosphere

The solar constant (intensity of solar radiation outside the Earth s atmosphere at die mean distance between die earth and the sun) has been determined by measurements from satellites and high-altitude aircraft and is 1.353 kilowatts per square meter. This extraterrestrial radiation,... 

The measurement of the spectral distribution of solar radiation outside the atmosphere and the subsequent association of this spectral distribution with the spectral distribution of radiation in a blackbody cavity has, I believe, biased the attempts to characterize the actual radiation in the atmosphere to an undue extent. Figure 1 indicates typical spectral distributions of radiation in the atmosphere as compared to that of solar radiation outside the atmosphere. Outside the atmosphere m 0 and if the flux is directly through m 1. If slanted at and angle from the zenith angle 90, then m is approximately 1/cos 60. 

Figure 1.1 Spectra of the solar radiation outside the Earth s atmosphere ( ) and at ground...

Figure 2-5 shows the spectral distribution of solar radiation outside the earth s atmosphere and the direct flux reaching the ground surface. Table... 

The density of the atmosphere varies greatly from place to place, as does its composition and temperature. The average composition of dry air (air from which water vapor has been removed) is shown in Table 4.4. One reason for the nonuniformity of air is the effect of solar radiation, which causes different chemical reactions at different altitudes. The density of air also varies with altitude. For example, the air outside an airplane cruising at 10 km is only 25% as dense as air at sea level. 

Specific solar radiation conditions are defined by the air mass (AM) value. The spectral distribution and total flux of radiation outside the Earth s atmosphere, similar to the radiation of a black body of 5,900 K, has been defined as AM-0. The AM-1 and AM-1.5 are defined as the path length of the solar light relative to a vertical position of the Sun above the terrestrial absorber, which is at the equator when the incidence of sunlight is vertical (90°) and 41.8°, respectively. The AM-1.5 conditions are achieved when the solar flux is 982 Wm2. However, for convenience purpose the flux of the standardized AM-1.5 spectrum has been corrected to 1,000 Wm2. 

It is quite apparent from Fig. 8-63 that solar radiation which arrives at the surface of the earth does not behave like the radiation from an ideal gray body, while outside the atmosphere the distribution of energy follows more of an ideal pattern. To determine an equivalent blackbody temperature for the solar radiation, we might employ the wavelength at which the maximum in the spectrum occurs (about 0.5 /im, according to Fig. 8-63) and Wien s displacement law [Eq. (8-13)]. This estimate gives... 

Solar Radiation. Of all the factors which collectively determine the amount and spectral distribution of the radiation entering a surface layer of the atmosphere, the best established appear to be the spectral irradiance outside the atmosphere and the attenuation by molecular scattering. The absorption coefficients of ozone are well established, but no easy method exists for determining the amount of ozone in a vertical profile of the atmosphere at a given time. The measurement of the particulate content of the atmosphere and its correlation with atmospheric transmission is a field in which much remains to be accomplished. Surprisingly few data exist on the spectral distribution of sky radiation and its variation with solar elevation and atmospheric conditions. The effect of clouds is of secondary importance, as intense smog generally occurs under a clear sky. 

The temperature of Earth is determined by the balance between solar radiation input (see Fig. 2-30) and reflection and reradiation of energy from Earth and its atmosphere back into space. Recall from Section 4.3.1 that the solar constant is approximately 1400 W/m2. The projected area intercepting the solar radiation is 7rr2, where r is Earth s radius. Given that Earth s surface area is 47rr2, the average solar radiation received outside Earth s atmosphere is approximately one-fourth the solar constant, or 350 W/m2. 

The large distance between sun and earth means that solar radiation forms a quasi-parallel bundle of rays. The radiation that is not yet weakened by scattering and absorption in the earth s atmosphere is called extraterrestrial radiation. If it is perpendicularly incident on a surface just outside the earth s atmosphere, at a distance r0 = 1 AU from the centre of the sun then the irradiance of the extraterrestrial solar radiation is called the solar constant E0. By evaluating more recent measurements, C. Frohlich and R.W. Brusa [5.33] determined the value... 

Fig. 2. Ozone effect on solar radiation (left) and dependence of ozone concentration on atmospheric altitute (right). In the left part the dotted curve represents the photon distribution of solar energy outside the atmosphere (based on the assumption of black body radiation at T = 5773 K). The full curve gives the photon distribution of solar radiation reaching earth surface (see Ref.8. The ozone effect is shown by shadowed area, the dicline above 800 nm is mainly due to absorption by water vapour. On the right side the full curve represents qualitatively a typical ozone profile, the real ozone distribution significantly depends on the local situation (geography), see Ref.15)...

The solar constant is defined as the total radiative energy flux outside the Earth s atmosphere. This parameter is used to characterize the total solar radiation input. The magnitude of this constant is estimated by Brusa and Frohlich (1982) to be 1367 W m-2, at 1 AU (astronomical unit), which corresponds to an effective solar temperature of 5780 K. 

The solar spectrum outside the Earth s atmosphere extends from about 200 nm to 2500 nm, half of the energy being concentrated in the visible part of the spectrum, 40% in the infrared, and 10% in the ultraviolet. Practically all the radiation below 295 nm is. filtered out by the atmosphere so that the solar energy reaching the Earth s surface is distributed according to the spectrum shown in Fig. 1 [1]. 

Table 2-7. Some Photochemically Active Trace Constituents of the Atmosphere and Associated Photodissociation Coefficients Calculated from the Solar Radiation Flux Outside the Earth Atmosphere (Nicolet, 1978) ...

Here B is the world average burden of anthropogenic sulfate aerosol in a column of air, in grams per square meter. The optical depth is then used in the Beer Law (which describes the transmission of light through the entire vertical column of the atmosphere). The law yields I/Iq = where I is the intensity of transmitted radiation, Iq is the incident intensity outside the atmosphere and e is the base of natural logarithms. In the simplest case, where the optical depth is much less than 1, (5 is the fraction of light lost from the solar beam because of... 

Any other body which has absorptivity a fiw) = 1 for photons with energy Hui will emit radiation according to (4.1). Although the sun consists mainly of protons, alpha particles and electrons, its absorptivity is a(Tkj) = 1 for all photon energies tiw, by virtue of its enormous size. Its temperature is not homogeneous, but emitted photons originate from a relatively thin surface layer a few hundred kilometres thick, in which the temperature is constant and in which all incident photons are absorbed. Conversely, only photons emitted within this surface layer may reach the surface of the sun. The solar spectrum observed just outside the Earth atmosphere agrees well with (4.1)... 

An alternate technique uses the back-scattered solar ultraviolet (BUV) radiation reflected into space and measured outside the atmosphere from an orbiting satellite. The vertical distribution of ozone within this total column can be measured with the ground-based Dobson instrument through the umkehr technique, which depends upon the variation in ultraviolet penetration versus solar zenith angle over a period of several hours. The vertical distribution of ozone can also be determined from the wavelength dependence of the BUV signal. 

I2-65C What fraclioo of the solar energy is in the visible range (o) outside the earth s atmosphere and (b) at sea level on earth Answer the same question for infrared radiation. 

The rate at which solar energy is received just outside the Earth s atmosphere on a surface that is normal to the incident radiation and at the mean distance of the Earth from the sun. The current value is 0.140 watt/cm2. solar cycle... 

Primary cosmic radiation, in the form of high energy nuclear particles, electrons and photons from outside the solar system and from the Sun, continually bombards our atmosphere. Secondary radiation, resulting from the interaction of the primary cosmic rays with atmospheric gas, is present at sea-level and throughout the atmosphere. 

The sun s energy at the earth s surface varies continuously in time and space. The solar constant derived from ground-based measurements has varied from 1323 to 1428 W m (1). Outside the atmosphere (air mass = 0) the sun s energy is more predictable (American Society for Testing and Materials [ASTM, E490]). At the annual mean solar distance from the sun, we define a solar constant of radiation for the earth. This is the measured amount of solar energy flux incident normally on a unit area in a unit of time (1.373 0.008 x 10 erg/sec cm ). Typical atmospheric absorbers (water, ozone, CO2, dust, and industrial pollutants) scatter and absorb... 

The astronomical investigations of space are not restricted solely to optical radiations. Space technology, starting with ballistic rockets and, in particular, satellite technology, have enabled astronomers to study X-ray sources which are the result of interstellar catastrophical events such as the collapse of a solar system. These observations are only possible outside the atmosphere of the Earth (see Sect. 4.3.3). 

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