340 
By this method, temperatures for January 1947 taken 
on a world-wide basis range between 100K and 500K 
for the E-region; between 50K and 1500K for the F,- 
region; and between 100K and 1000K for the F-region. 
The ranges indicated are a function of latitude and of 
local time; and probably of season, solar activity, and 
other factors. Thus there seems to be a strong possi- 
bility of beimg able, in the near future, to calculate 
from the dynamics of the situation the probable wind 
systems in the ionosphere and to mvestigate possible 
connections between the ionosphere and lower-atmos- 
phere meteorology. 
Aside from electromagnetic-wave propagation, the 
study of propagation of sound waves from large ex- 
plosions throws some light upon H-region temperatures. 
Preliminary results indicate H-region temperatures of 
the order of 400K for temperate latitudes. 
Probable Formation Mechanisms 
Wulf and Deming have given what appears to be 
the most acceptable discussion of causes of the iono- 
spheric structure. Their work, taken with that of 
Mohler, constitutes a good basis for further study as 
knowledge of the ionosphere develops. Only the D-, E-, 
and F-regions are examined by these authors. Knowl- 
edge of the probable existence of the G-region came at a 
time after these original papers had been presented. 
Wulf and Deming have shown that above about 100 
km oxygen atoms predominate and that below about 
100 km oxygen molecules predominate (other con- 
stituents bemg the same) and have assumed a temper- 
ature of 219K up to 100 km, with a temperature of 
700K above 100 km, and have consequently decided 
that the F.- and Fj-regions are caused by two distinct 
nitrogen-molecule absorptions and that the H-region is 
the result of oxygen-molecule absorption. According to 
these authors, the D-region is the result of a broad 
absorption by ozone. By inference, using arguments of 
Wulf and Deming not elaborated upon by them in 
terms of later experimental evidence, it may be that 
the E»-region is formed by oxygen-atom absorption and 
that the G-region is developed through nitrogen-atom 
absorption. 
It appears in light of later work on ionospheric 
temperatures that the temperatures assumed by Wulf 
and Deming may not be correct. However, alteration of 
the temperature arrangement to what seem to be more 
appropriate values will only change somewhat the 
heights where maximum absorptions occur. In fact, the 
THE UPPER ATMOSPHERE 
adoption of the more recent temperature postulates 
will improve the results of Wulf and Deming, giving 
better agreement between their deductions and the 
experimental information about the location of the 
regions. 
Need for Additional Studies 
While many observations of the ionosphere as de- 
duced from electromagnetic-wave propagation have 
been made, a great portion of this information is poorly 
controlled from the standpomt of accuracy. Much of 
the available information is in the form of short series 
of measurements over restricted frequency ranges. 
There is a great need for accurate, long-continued 
observations over all geographic locations. Only im this 
way can sufficient data be accumulated to permit satis- 
factory study of the ionosphere and its relationship to 
the lower atmosphere. In addition, the various theories 
need to be re-examined and extended to remove un- 
certainties now present. The region of ten to twelve 
degrees above and below the equator at all longitudes 
is In great need of exploration. Both north and south 
polar areas are virtually unexplored. In all but polar 
regions it is entirely feasible for the governments of 
countries considered civilized to establish permanent 
observatories for study of the ionosphere. Such pro- 
grams must lead to results of importance from many 
viewpoints. 
Tt is quite difficult, on the other hand, to establish 
stations within about 25 degrees of either pole. It is 
suggested that with modern high-speed ionospheric re- 
corders it is entirely within the realm of possibility to 
make systematic ionospheric measurements from long- 
range aircraft. Such a program, ideally, should be a 
cooperative one engaged in jointly by all nations, and 
particularly by those bordering upon the polar areas. 
REFERENCES 
Examination of the following basic books contaiming bibli- 
ographies will permit all references in the text to be identified, 
and will permit location of a large body of additional material. 
Cuapman, S., and Barris, J., Geomagnetism. Cambridge, 
University Press, 1940. 
Fuemine, J. A., ed., Physics of the Harth—VILI, Terrestrial 
Magnetism and Electricity. New York, McGraw, 1939. 
Mannine, L. A., Final Engineering Report on High Altitude 
Radio Frequency Propagation. Palo Alto, Electronics Re- 
search Laboratory, Stanford University, 1947. 
Mirra, S. K., The Upper Atmosphere. Calcutta, The Royal 
Asiatic Society of Bengal, 1948. 
