Scattering of Solar Radiation

In the Charlson et al. (1992a) and Penner et al. (1994) estimates, Bsoi = 3.3 X 105 mol m-2, with uncertainties in QSOi, ysullate, and rsullatc of 1.15,1.5, and 1.5, respectively. (Note, however, that some subsequent studies have suggested that direct radiative forcing may vary nonlinearly with the sulfate concentration due to chemical interactions with other particle constituents e.g., see West et al., 1998.) 

The largest uncertainties are associated with the aerosol radiative properties (3, aIUI, and /RH, which is particularly sensitive to the treament of the dependence on relative humidity (vide infra), and with the amount of sulfate (i.e., in Bso2-) available to scatter light. Other sensitivity analyses also suggest that uncertainties in ysuir,llt, and rsuiratc, and hence in as 

Water uptake affects light scattering by particles due to changing the particle size and the index of refraction. This has been discussed in detail in Chapter 9.B.4 and the reader is referred to that section for more 

FIGURE 14.27 Calculated fraction of 550-nm light scattered upward (/3) as a function of solar zenith angle (0) and particle radius (yum). The refractive index of the particles is 1.4 (adapted from Nemesure et al., 1995). 

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Spectra can be readily measured accuracy of data can be increased through least-mean-squares data analysis. Consequently, the effects of absorption or scattering of solar radiation can be determined with sufficient accuracy. 

B) Once these particles have grown beyond about 50 nm in particle diameter they will affect radiation budgets due to direct scattering of solar radiation as well as due to changing cloud properties (indirect effects). 

Particulate material, other than water or ice, in the atmosphere ranging in size from approximately lOx-3 to larger than 10x2 m in radius. Aerosols are important in the atmosphere as nuclei for the condensation of water droplets and ice crystals, as participants in various chemical cycles, and as absorbers and scatterers of solar radiation, thereby influencing the radiation budget of the earth-atmosphere system, which in turn influences the climate on the surface of the Earth, agglomeration... 

Aerosols may also play an important role in cHmate change. Natural aerosol emissions, similar to those caused by volcano eruptions and forest fires, can affect the radiation balance around the planet and, therefore, affect global temperatures quite distinctly from the heat directly released in such phenomena. Atmospheric aerosol emissions resulting from human industrial and deforestation activities can have the same effect, distinct from the associated greenhouse gas emissions. In both cases, these aerosols influence climate through the scattering of solar radiation, the absorption of terrestrial radiation, and through their effects on the properties of clouds [128, 129]. 

In the temperate latitudes of 35 45°, scattering of solar radiation increases significantly due to the longer atmospheric path length resulting from latitude and lower solar azimuth. Clouds and atmospheric pollution and particulates result in decreased incident radiation. Above 45° latitude almost half of the incident solar radiation is diffuse scattered sky and not direct beam. 

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