SOLAR RADIANT ENERGY 3l 
malous solar energy Q might imfluence the air tem- 
perature in inland areas with a lag in the same way 
as the normal surface air temperature lags the normal 
solar radiation. If such an effect could be found, the 
forecasting value of the observed solar radiation would 
be obvious. 
Other studies involving the observed anomalous ra- 
diation may be profitable. The average annual cycle of 
atmospheric circulation is of course related to, if not 
entirely caused by, the change in the gradient of solar 
heating of the earth’s surface. Here again perhaps study 
of the observed anomalous radiation distribution for a 
week or a month may reveal it to be a factor in the 
cause of large-scale weather changes. 
The Albedo of the Earth. To a certain extent the 
previous remarks concerning the significance of the dis- 
tribution of surface heating apply also to the heating 
of the entire planet. The planet-wide heating cannot be 
observed at present from surface observations. How- 
ever, by Danjon’s technique the earth’s albedo can be 
observed, although corroborating independent observa- 
tions are highly desirable. Furthermore, by making 
observations from several longitudes it may even be 
possible to estimate the longitudinal distribution of the 
albedo and therefore of the heating. The variations of 
these albedos from their average values may be related 
to the subsequent exchange of heat and of masses of the 
atmosphere between latitudes and between longitudes. 
Upper-Atmospheric Heating. The uncertainties re- 
garding the extent of heating in the ozone layer were 
discussed earlier and a quasi-practical experiment to 
determine the fluctuation of radiation during SID’s was 
proposed. It is, of course, possible to attempt correla- 
tions of numerous solar parameters with meteorological 
parameters. The number, size, shape, and polarity of 
sun spots, as well as faculae, flocculi, prominences, and 
coronal lines are but a few of the parameters which 
have been or could be used. However, it seems to the 
author that if any relation does exist between solar 
variability and tropospheric meteorology over a period 
of a few days or longer, those solar parameters which 
are known to produce effects somewhere in the upper 
atmosphere would offer the greatest promise, and it 
would be better to seek correlations not with the solar 
variation itself but rather with the known terrestrial 
effect which has been produced. Prominent among such 
_ Solar-induced terrestrial effects are SID’s and magnetic 
variations. 
The suggestion then is that we measure the variation 
of solar ultraviolet radiation which reaches the top of 
the ozone layer, and the variation of temperature there. 
Until such measurements are made we cannot be sure 
that solar variation is heating the ozone layer signifi- 
cantly above its normal temperature. After the magni- 
tude of ozone heating has been established, correlations 
of tropospheric effects with solar parameters which 
produce the ozone heating would obviously be indi- 
cated. In the meantime, the SID seems to be a par- 
ameter which is likely to be related to abnormal ozone 
heating; as such it may be related to surface pressure 
changes. 
Absorption by Clouds. Since some of the measure- 
ments suggest large absorption of solar energy by 
clouds, it would be desirable to investigate the absorp- 
tion further. This can be done from airplanes, as de- 
scribed earlier; but it may also be feasible to investigate 
the absorption from the ground. This might be ac- 
complished by spectroscopic measurements on clouds 
from \ = 0.5 to \ = 2.5 yu. On the basis of the data of 
Fig. 1 and our knowledge of the spectral distribution 
of clear-sky light [55], we can approximate the spectral 
distribution of the solar energy which irradiates the 
tops of clouds. Furthermore, Fig. 7 shows the extinc- 
tion of parallel light by droplets in the absence of ab- 
sorption, and shows that if the droplets are large (2r7r/d 
> 50), K, becomes nearly independent of for the 
spectral region between 0.5 » and 2.5 u. This ought to 
be true also for diffuse radiation such as that produced 
by clouds. At 0.5 » the absorption coefficient of liquid 
water is in reality very small, so that the extinction by 
clouds at 0.5 » is caused wholly by scattering. Conse- 
quently J).5, the measure of spectral intensity at 0.5 y, 
can serve as a standard against which to compare the 
spectral intensities at longer wave lengths such as 2.0 u. 
From Fig. 7, together with some reasonable assump- 
tion about the droplet sizes in the cloud and the relative 
spectral irradiation of the cloud top, we can calculate 
Too relative to I) on the assumption that no absorp- 
tion is present. The difference between the calculated 
I, and the observed [9 might serve as a first approx- 
imation to the absorption. Greater refinement can prob- 
ably be obtained from Mecke’s theoretical discussions 
[59]. 
Conclusion. We have discussed the state of our knowl- 
edge in the field of solar radiation and speculated about 
some of the deficiencies in that knowledge and in its 
application to meteorology. On the question of the solar 
energy potentially available for “use,” the suggestions 
(1) that the albedo (35 per cent) of the earth is smaller 
than the value (43 per cent) which has often been ac- 
cepted, and (2) that the absorption by clouds is higher 
than formerly assumed may require a re-evaluation of 
the disposition of the radiation received by the earth 
in the mean. That the long-term average radiative bal- 
ance controls the average weather pattern is, of course, 
not subject to question. The excess or deficit of ab- 
sorbed solar radiation by comparison with the normal 
absorbed radiation should also significantly mfluence 
the weather elements averaged over relatively short 
periods. Whether a week, a month, a season, or longer 
is the required ‘relatively short period” remains to be 
investigated. 
REFERENCES 
An attempt has been made to limit the number of references. 
Many of those listed here contain additional useful ones. A 
relatively large number of references are contained in several 
of the items listed below; these have been marked with an 
asterisk. 
1. Asgot, C. G., ‘The Variations of the Solar Constant and 
Their Relation to Weather. Reply to Paranjpe and 
Brunt.’ Quart. J. R. meteor. Soc., 65:215-236 (1939). 
2. —— Fowtr, F. E., and Avupricn, L. B., ‘The Distribu- 
