RADIATIVE TEMPERATURE CHANGES IN THE OZONE LAYER 
By RICHARD A. CRAIG 
Harvard College Observatory 
THE OZONE LAYER 
2?) 
The term ‘‘ozone layer” as used here refers to that 
part of the atmosphere that lies above the tropopause 
and below about 60 km. The bulk of the atmospheric 
ozone lies in this region. The physical characteristics 
of the ozone layer have been studied, principally from 
the surface of the earth, by various indirect methods. 
Some of the conclusions reached by these methods, 
however, have been verified by a few direct measure- 
ments obtamed by means of manned and unmanned 
sounding balloons and rockets. 
The present state of knowledge with regard to the 
ozone layer is outlined elsewhere in this volume by 
Gotz. Gotz has also presented a very complete sum- 
mary of ozone work as of the year 1938 [20] and in a 
more recent paper has brought this summary up to the 
year 1944 [21]. Even more recently Craig [10] has given 
a somewhat less comprehensive summary. Neverthe- 
less, in order that this contribution may be more or less 
self-contained, certain basic facts about the ozone layer, 
particularly those that are necessary to an understand- 
ing of the remainder of this paper, are outlined briefly 
in this section. 
Ozone Distribution. The total amount of ozone in a 
vertical column above the earth’s surface is small com- 
pared to that of other atmospheric constituents, namely, 
about 0.38 em at NTP.? Nevertheless, because of its 
absorbing qualities, ozone is an extremely important 
constituent of the atmosphere. 
A large number of measurements at the earth’s sur- 
face have determined the variations with season and 
geographical position of this total amount of ozone.’ 
At a given place on the earth, the ozone amount is a 
maximum in the early spring and a minimum in the late 
fall. The total ozone amount is a minimum at the equa- 
tor and increases toward higher latitudes. At least in 
the Northern Hemisphere, it apparently reaches a max- 
imum near 60°N and decreases poleward from there. 
A further interesting feature of ozone distribution in 
middle and high latitudes is that the total amount of 
ozone above a given place may vary markedly from 
day to day. The amplitude of this variation of daily 
values in any given month may be as large as the ampli- 
tude of the annual variation of the monthly means. 
Moreover, the day-to-day ozone variations reveal marked 
correspondence to weather conditions at the surface, 
1. See “Ozone in the Atmosphere”? pp. 275-291 of this 
Compendium. 
2. Ozone amounts are generally expressed in terms of the 
height of the resulting volume of ozone if all the ozone in the 
column were brought to normal temperature and pressure at 
the earth’s surface. 
3. For references to published series of ozone observations, 
see [10]. 
as shown by Dobson [12], Lejay [387], and Ténsberg 
and Olsen [55]. 
The vertical distribution of ozone has been most gen- 
erally studied by means of the Umkehr effect. This ef- 
fect, first noted by G6tz at Arosa and applied by Gotz, 
Meetham, and Dobson [22], refers to the observations 
of scattered zenith light when the sun is near the hori- 
zon. The ratio of the intensities of two wave lengths, 
both absorbed by ozone but to different degrees, de- 
creases as the sun nears the horizon, reaches a mini- 
mum, and then increases. This phenomenon results 
from the fact that the effective height of scattermg 
increases as the sun nears the horizon and finally lies 
above the ozone layer. The shape of the Umkehr curve 
may be used to deduce the vertical distribution of 
ozone, as has been shown by Gotz, Meetham, and Dob- 
son [22] for Arosa observations. Meetham and Dobson 
at Troms6 [40], T¢nsberg and Olsen at Troms6 [55], 
and Karandikar and Ramanathan at Delhi and Poona 
[33] have also applied the method. The Umkehr method 
is only approximate, but its results have been verified 
by various direct measurements [8, 9, 43, 47, 51]. The 
measurements show that the maximum density of ozone 
occurs between 20 and 30 km and that it decreases 
rapidly above the level of maximum. The density of 
ozone below the maximum level is quite variable. In 
fact, the observations show that most of the variability 
in the total amount of ozone (latitudinal, seasonal, and 
day-to-day) reflects variability between the tropopause 
and the level of maximum ozone. 
Temperature Distribution. The temperature distribu- 
tion in the ozone layer, at least above 30 km, is less 
well known. In the vertical, the temperature between 
the tropopause and about 30 km is nearly isothermal. 
This region has been studied directly by radiosonde. 
Above 30 km, mainly indirect evidence points to a 
rapid increase of temperature with height, reaching a 
maximum at 50-60 km. This evidence is based on 
observations of the anomalous propagation of sound 
[58] and of the characteristics of meteor trails [88, 59, 
60]. Recently, measurements from a V-2 rocket have 
verified this qualitative picture [31]. 
In the lower, isothermal region, where direct meas- 
urements are available, seasonal and latitudinal vari- 
ations of temperature are known. In the summer, the 
temperature is lowest over the equator and increases 
toward the poles. In the winter, the poleward increase 
of temperature also occurs in lower latitudes, but a 
maximum of temperature occurs in middle latitudes 
and the temperature is again lower at higher latitudes 
[29]. At a given point in middle latitudes the maximum 
temperature in the lower part of the ozone layer occurs 
just before the summer solstice, the minimum just be- 
fore the winter solstice. This contrasts with the behavior 
of the upper troposphere, where the maximum and 
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