294 
by Haurwitz [28], that solar variability may affect the 
ozone layer directly and our weather indirectly. Solar 
variability in the visible is at best very small, while in 
the ultraviolet it appears, from various phenomena in 
the upper atmosphere, to be large. The ozone layer is a 
strong absorber of solar ultraviolet radiation and is 
situated at a level in the atmosphere where there is still 
appreciable mass. This interesting question, then, lends 
added importance to the whole problem of the size and 
distribution of radiative changes in the ozone layer. 
HEATING OF THE OZONE LAYER 
Several different radiative processes serve to heat 
the ozone layer. Most of these processes involve the 
absorption, by some constituent of the atmosphere, of 
energy from the direct solar beam. The lower part of 
the ozone layer, however, is also heated by absorption 
of infrared radiation from the earth’s surface and from 
the troposphere and by ozone absorption of solar energy 
reflected and scattered from the troposphere. 
The next section, on cooling of the ozone layer, deals 
with the absorption characteristics of atmospheric gases 
in the infrared. The general information pertinent to 
the question of heating due to infrared absorption is 
available there. In this section, only general considera- 
tions relative to the question of absorption im the ultra- 
violet and visible are included. In a later section some 
numerical results from computations will be presented. 
Ozone Absorption. Ozone is the most important con- 
stituent of the ozone layer from the point of view of 
absorption of solar energy. Particularly, the Hartley 
bands (2000-3200 A) absorb strongly and are respon- 
sible for the sharp cut-off of the solar spectrum near 
3000 A. 
SOLAR BEAM 
Fic. 1.—Solar beam passing through the ozone layer when 
the sun is at the zenith angle Z. 
In Fig. 1, let a parallel beam of radiation from the 
sun be incident at the top of the ozone layer at an 
angle Z from the vertical. In the spectral interval dA 
let the intensity of the mcident solar radiation be Jo, 
and call the ozone absorption coefficient a. Consider 
a column of air that is parallel to the solar beam and 
that has unit cross section. While passing through a 
THE UPPER ATMOSPHERE 
vertical distance dz, the solar intensity in d\ is decreased 
by the amount 
dl, = Iha,n sec Z dz, (8) 
where n is the amount of ozone per unit volume and 
I, is the intensity at the level z. The sign in (8) is 
positive because z is taken positive upward. Equation 
(8) can be integrated to give 
Ty = Ip, exp (-/ an sec Z az). (9) 
The energy absorbed per unit volume in the spectral 
interval dd is 
dl 
sec Z dz 
dy = Inn ayn exp (—a) N) dx, (10) 
where 
N 
/ n sec Z dz (11) 
is the total amount of ozone the solar energy has tra- 
versed in its oblique path above the level z. The total 
energy absorbed per unit volume at the level z is 
= iby 
a, = || 
0 sec Z dz on 
Een [ Jlnvon OD (ani) Br 
0 
(12) 
In practice, the integration in (12) needs to be taken 
only over the spectral interval of appreciable ozone 
absorption; namely, the Hartley bands (2000-3200 A), 
the Huggins bands (8200-3600 A), and the Chappuis 
bands (4500-6500 A). The spectrum can be divided 
into several finite intervals characterized by appro- 
priate mean values of Jo, and ay. Then (12) is a func- 
tion only of NV. Later in this section (Fig. 2) H./n is 
shown graphically as a function of N for specific spectral 
distributions of 7 and ay. 
The rate of heating of the unit volume is then 
oipmaape 
patel, = ; 1 
ot Cp p (13) 
where C, is the specific heat of air at constant pressure, 
which has the value 0.239 cal g+ deg, and p is the air 
density, which of course varies with elevation. 
In the Huggins and Chappuis bands, a large part of 
the extraterrestrial solar radiation penetrates the ozone 
layer and is later scattered and reflected back from the 
troposphere to be absorbed by the ozone. The treat- 
ment of this phase of the problem is quite similar to 
the discussion above, except that the radiation is dif- 
fuse rather than parallel. The equation corresponding 
to (12) is 
ae | logan PACAIN Gk 
fio 3 sec Z y 
where J, is the intensity reaching the troposphere in 
the spectral interval d\. The exponential transmission 
(14) 
= 
