Atmosphere, solar radiation

Periodic climate changes due to variations in extra-atmospheric solar radiation. 

The change in extra-atmospheric solar radiation is a climate-forming factor that should be considered. The contribution of such a change to RF since 1750 might be as much as 20% compared with the contribution of C02. This is mainly explained by enhanced extra-atmospheric insolation in the second half of the 20th century (consideration of the 11-year cycle of insolation is vital here). However, the mechanisms that underly the impact of solar activity on climate are still far from being understood. Nonetheless, IPCC (2007) contains some conclusions and estimates. 

Solar Radiation in the Atmosphere Solar radiation is modified considerably on its path from the top of the atmosphere down to the sea surface. The simple radiation transport model used here follows mainly Bodin (1979), modified by Meier et al. (1999). The radiation at the sea surface is described as... 

Most ozone is formed near the equator, where solar radiation is greatest, and transported toward the poles by normal circulation patterns in the stratosphere. Consequendy, the concentration is minimum at the equator and maximum for most of the year at the north pole and about 60°S latitude. The equihbrium ozone concentration also varies with altitude the maximum occurs at about 25 km at the equator and 15—20 km at or near the poles. It also varies seasonally, daily, as well as interaimuaHy. Absorption of solar radiation (200—300 nm) by ozone and heat Hberated in ozone formation and destmction together create a warm layer in the upper atmosphere at 40—50 km, which helps to maintain thermal equihbrium on earth. 

At 25°C, pH 7.5, 1.5 ppm FAC, and 25 ppm cyanuric acid, the calculated HOCl concentration is only 0.01 ppm. Although the monochloroisocyanurate ion hydrolyzes to only a small extent, it serves as a reservoir of HOCl because of rapid hydrolysis. Indeed, this reaction is so fast that HClCy behaves like FAC in all wet methods of analysis. Furthermore, since HClCy absorbs uv only below 250 nm, which is filtered out of solar radiation by the earth s atmosphere, it is more resistant to decomposition than the photoactive C10 , which absorbs sunlight at 250—350 nm and represents the principal mode of chlorine loss in unstabilized pools (30). As Httie as 5 ppm of bromide ion prevents stabilization of FAC by cyanuric acid (23) (see also Cyanuric and ISOCYANURIC acids). 

The ocean is an integral part of the climate system. It contains almost 96% of the water in the Earth s biosphere and is the dominant source of water vapour for the atmosphere. It covers 71% of the planet s surface and has a heat capacity more than four times that of the atmosphere. With more than 97% of solar radiation being absorbed that falls on the surface from incident angles less than 50" from the vertical, it is the main store of energy within the climate system. 

As discussed later, the enclosure of an IPB may carry induced currents up to 95% of the current through the main conductors. Accordingly, the enclosure is designed to carry longitudinal parasitic currents up to 90-95% of the rated current of the main busbars. The cross-sectional area of the enclosure is therefore maintained almost equal to and even more than the main conductors to account for the dissipation of heat of the main conductors through the enclosure only, unless an additional forced cooling system is also adopted. The outdoors part of the enclosure exposed to atmospheric conditions is also subjected to solar radiation. Provision must be made to dissipate this additional heat, from the enclosure. 

Much of the concern about particulate matter in the atmosphere arises because particles of certain size ranges can be inhaled and retained by the human respiratory system. There is also concern because particulate matter in the atmosphere absorbs and scatters incoming solar radiation. For a detailed discussion of the human respiratory system and the defenses it provides against exposure of the lungs to particulate matter, see Chapter 7. 

The principal components of atmospheric chemical processes are hydrocarbons, oxides of nitrogen, oxides of sulfur, oxygenated hydrocarbons, ozone, and free radical intermediates. Solar radiation plays a crucial role in the generation of free radicals, whereas water vapor and temperature can influence particular chemical pathways. Table 12-4 lists a few of the components of each of these classes. Although more extensive tabulations may be found in "Atmospheric Chemical Compounds" (8), those listed in... 

Reaction (12-9) shows the photochemical dissodation of NO2. Reaction (12-10) shows the formation of ozone from the combination of O and molecular O2 where M is any third-body molecule (principally N2 and O2 in the atmosphere). Reaction (12-11) shows the oxidation of NO by O3 to form NO2 and molecular oxygen. These three reactions represent a cyclic pathway (Fig. 12-4) driven by photons represented by hv. Throughout the daytime period, the flux of solar radiation changes with the movement of the sun. However, over short time periods (—10 min) the flux may be considered constant, in which case the rate of reaction (12-9) may be expressed as... 

The sun radiates approximately as a blackbody, with an effective temperature of about 6000 K. The total solar flux is 3.9 x 10 W. Using Wien s law, it has been found that the frequency of maximum solar radiation intensity is 6.3 x 10 s (X = 0.48 /rm), which is in the visible part of the spectrum 99% of solar radiation occurs between the frequencies of 7.5 X 10 s (X = 4/um) and 2 x 10 s (X = 0.15/um) and about 50% in the visible region between 4.3 x 10 s (X = 0.7 /rm) and 7.5 X 10 s (X = 0.4 /Ltm). The intensity of this energy flux at the distance of the earth is about 1400 W m on an area normal to a beam of solar radiation. This value is called the solar constant. Due to the eccentricity of the earth s orbit as it revolves around the sun once a year, the earth is closer to the sun in January (perihelion) than in July (aphelion). This results in about a 7% difference in radiant flux at the outer limits of the atmosphere between these two times. 

At angles away from the zenith, solar radiation must penetrate a greater thickness of the atmosphere. Consequently, it can encounter more scattering due to the presence of particles and greater absorption due to this greater thickness. 

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