56 RADIATION 
earth’s surface to the upper limit of the atmosphere, the 
temperature of the air within this column is determined 
primarily by the incoming and outgoing radiation, by 
the transfer of energy through horizontal advection, 
and, to some extent, by evaporation and condensation 
processes. If we take a column of a sufficiently large 
cross section and consider a sufficiently long time inter- 
val, our problem of analyzing the factors influencing 
the temperature coincides with the problem of finding 
the causes for climatological temperature changes in 
general. Here, incoming and outgoing radiation are the 
most fundamental elements. Without a thorough knowl- 
edge of these factors, their distribution and variations, 
all speculations on climatic variations are reduced to 
rather vague guesses. 
Another equally important problem, closely con- 
nected with the climatic variations, concerns the trans- 
mission of the atmosphere and its fluctuations. A clear 
ae 
90° 
Ss 
60° 30° o° 
LATITUDE 
30° 60° 90° 
N 
Fic. 2.—Preliminary curve showing variation of scattering 
coefficient 6 with latitude. 
separation between scattering and absorption is neces- 
sary. The simplest way of accomplishing this is indi- 
cated above. If we take the coefficient 8 as a measure of 
the scattermg of the atmosphere, the following remarks 
may be made. A rather summary treatment of avail- 
able pyrheliometric data already shows that 8 is on the 
whole much larger in tropical and subtropical regions 
than at higher latitudes. The graphical representation 
in Fig. 2, taken from a previous paper by the author 
[2], shows this, butit may be taken only as a very rough 
indication of the general conditions. More extensive 
observational data, systematically treated, must be 
available before the distribution of 8 over the whole 
globe can be mapped. Intensive investigations may 
here solve the problem concerning the dust-producing 
centers at the earth’s surface, the nature of the scatter- 
ing particles, and their origin under various conditions. 
Investigations near desert regions seem to show that 
the scattering particles directly produced by storms 
over the desert are much larger than those which 
generally occur in the atmosphere. At all Northern 
Hemisphere stations investigated for an annual varia- 
tion of 8, the scattering coefficient reaches a pronounced 
maximum in the sprmg (April or May). The values of 
6 obtained at Spitsbergen by Olsson [8] and at Abisko 
(northern Lapland) by Tryselius [11] are so low that 
the scattering there must be almost totally due to the 
molecules. Therefore, if we consider only the effect of 
scattering, the ultraviolet radiation at, for instance, 
30° solar elevation in Lapland, must be almost as in- 
tense as at about 2000-m height in Switzerland for the 
same solar elevation. Only a few of the problems re- 
lated to a more detailed synoptic investigation of scat- 
termg in the atmosphere have been indicated here. 
The outgoing “effective radiation” should be the 
object of a closer investigation especially with respect 
to its distribution over the earth’s surface. In general, 
it seems to be very closely related to two factors: (1) 
the temperature at the place of observation and the 
temperature distribution in the atmosphere, and (2) 
the content of water vapor in the atmosphere. This rela- 
tionship is so close that it is doubtful whether there 
are any other factors whose effects do not fall within 
the errors of observation. On the other hand, there are 
some indications of a variation during the night, which 
might not be explained by a variation of the previously 
mentioned elements. Here is an important field of 
research from which perhaps some factor influencing the 
climatic variations may be discovered. 
Finally, for the important studies of the relation 
between biological phenomena and radiation, an actino- 
metric network has an essential task to fulfill. In all 
these studies in which special portions of the spectrum 
must be considered effective, a clear separation between 
scattering and absorption is necessary. When we know 
the scattering coefficient and its variations, we will be 
able to give a much more detailed picture of the varia- 
tions in the different spectral regions of the sun’s 
radiation. Such a detailed knowledge is probably neces- 
sary before the relation between biological pheno- 
mena and solar radiation can be investigated with 
success. 
REFERENCES 
1. Anesrré, A., “On the Atmospheric Transmission of 
Sun Radiation and on Dust in the Air.” Geogr. Ann., 
Stockh., 11:156-166 (1929). 
— “On the Atmospheric Transmission of Sun Radiation, 
Il.” Lbtd., 12:130-159 (1980). 
3. —— “Survey of the Activities of the Radiation Commis- 
sions of the International Meteorological Organisation 
and of the International Union of Geodesy and Geo- 
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—— “Atmospheric Circulation, Climatic Variations and 
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iS) 
a 
