Solar Radiation in the Atmosphere

10 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 

Qo is the solar radiation at the top of the atmosphere and Tu = 0.95 is the transmissivity of the upper atmosphere. The albedo a is calculated from the Fresnel formula (Kondratyev, 1969). The quantities Tr and Ab are transmissivity and absorption in the atmospheric boundary layer. 

The cosine of the sun s zenith angle 5 depends on time, latitude, and longitude. The optical path length t exhibits a seasonal cycle mainly due to a variable content of water vapor. It should be noted that this formula refers to the present state of the atmosphere and may need modification to simulate the Baltic Sea of the past or future. 

---

FIGURE 3.13 Approximate regions of maximum light absorption of solar radiation in the atmosphere by various atomic and molecular species as a function of altitude and wavelength with the sun overhead (from Friedman, 1960). 

Table 4.3 Spectral distribution of the optical solar radiation in the Earth s atmosphere. Data taken from the Smithsonian Physical Tables (1959)...

In Chapter 3 we examined the interaction of incoming solar radiation in the UV and visible regions of the spectrum with atmospheric gases, which drives atmospheric photochemistry. This incoming solar radiation... 

The main objective of the PAUR I project was to investigate how increased penetration of UV-B solar radiation through the atmosphere, resulting from stratospheric ozone depletion, affects photochemical production and chemical transformation of ozone and other photochemically active species in the lower atmospheric layers. 

Atmospheric ozone constitutes 0.64 10 6 of the atmospheric mass and belongs to the class of optically active gases. It absorbs UV solar radiation in the range 200 nm 300 nm, strongly affecting thereby the thermal regime of the stratosphere. Moreover,... 

Clouds and the Earth s Radiant Energy System (CERES) CERES is a broadband three-channel scanning radiometer. One channel measures reflected solar radiation in the range 0.3 pm-5.0 pm. Two other channels (0.3 pm-100 pm and 8 pm-12 pm) measure reflected and emitted radiant energy at the top of the atmosphere. 

Melnikova I.N. and Vasilyev A.V. (2004). Short-Wave Solar Radiation in the Earth s Atmosphere. Springer-Verlag, Berlin, 303 pp. 

Fig. 3. The absorption spectrum for solar radiation in the Earth s atmosphere 19X On the ordinate is plotted the altitude at which the radiation intensity is reduced by a factor e 1 from its unattenuated value. The species predominantly responsible for the absorption in the various wavelength ranges are as indicated. The wavelength of the H Lyman-a radiation closely coincides with a window in the O2 absorption spectrum...

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. 

For different rainout rates we have calculated widely different transmission of solar radiation through the atmosphere. For slow rainout rates, the transmission may remain below 10% for a whole month (see Figure 2), which means that sunlight transmission would be less than 1%, if twice the amount of aerosol were to be dumped in the atmosphere. Because of the uncertain analysis of the amounts of fuels burnt and particulate matter formed from different materials, and considering also the simplicity of the model adopted in this study, this possibility may not be discounted. A prolonged stay of aerosol particles in the atmosphere would occur if much particulate matter rapidly reached the stratosphere because of the intense solar heating of the smoke clouds. 

There has been recent interest in a somewhat different aspect of adsorption and reaction on metal oxides photocatalysis. The interest stems partially from that role that some transition-metal oxides can play in photochemical reactions in the atmosphere. Atmospheric aerosol particles can act as substrates to catalyze heterogeneous photochemical reactions in the troposphere. Most tropospheric aerosols are silicates, aluminosilicates and salts whose bandgaps are larger than the cutoff of solar radiation in the troposphere (about 4.3 eV) they are thus unable to participate directly in photoexcited reactions. However, transition-metal oxides that have much smaller bandgaps also occur as aerosols — the most prevalent ones are the oxides of iron and manganese — and these materials may thus undergo charge-transfer excitations (discussed above) in the pres-... 

The growth law for a polydisperse aerosol can be determined by measuring the change in the size distribution function with lime. In experiments by Heksler and Friedlander (1977), small quantities of organic vapors that served as aerosol precursors were added to a sample of the normal atmospheric aerosol contained in an 80-m bag exposed to solar radiation. The bag was made of a polymer film almost transparent to. solar radiation in the UV range and relatively unreactive with ozone and other species. Chemical reaction led to the formation... 

From the foregoing parts of this book it is clear that solar radiation in the stratosphere is primarily attenuated by ozone (see Subsection 3.4.3) and at a lesser extent by the stratospheric sulfate aerosol layer (see Subsection 4.4.3). This means that any change in the stratospheric 03 burden or aerosol concentration involves modification of radiative transfer in this atmospheric domain. We should remember that the residence time of trace constituents above the tropopause is rather long because of the thermal structure and the absence of wet removal. Furthermore at these altitudes the density of the air is low as compared to that of lower layers. For this reason even an insignificant quantity of pollutants can produce relatively long and significant effects. 

As shown by Johnston and Selwyn (1975), the cross section of N2O varies strongly with temperature. The quantum yield for photodissociation is unity, and the products are N2 and 0(1D). The atmospheric photolysis rate comes predominantly from the absorption of solar radiation in the 02 Herzberg continuum and Schumann Runge bands. Jn2o 9 x 10-7s-1 for A > 175 nm. 

Atmospheric pollution by itself introduces another problem it reduces the quantity of solar radiation that reaches the Earth s surface. According to data released from studies of the oceans and the atmosphere above the US by a US health agency, solar radiation in the period from 1950 to 1972 decreased by 8% during the fall season, and increased by only 3% in the spring. On the average, solar radiation has fallen by 1.3% since 1964. This is equivalent to the loss of approximately 10 minutes of daylight per day. This apparent triviality can have serious consequences on the Earth s climate. 

If all the atmospheric ozone were compressed into a single layer at STP on Earth, that layer would be only about 3 mm thick Although the concentration of ozone in the stratosphere is very low, it is sufficient to filter out (that is, absorb) solar radiation in the 200- to 300-nm range [see Equation (17.3)]. hi the stratosphere, it acts as our protective shield against UV radiation, which can induce skin cancer, cause genetic mutations, and destroy crops and other forms of vegetation. 

---