THE IONOSPHERE 
Relations between the Ionosphere and Surface Me- 
teorology 
When it is remembered that postulates concerning 
the existence of the ionosphere originated with mathe- 
maticians and magneticians and that proof of the reality 
of the ionosphere was given by engineers and physicists, 
it is not astonishing to observe that many years passed 
before the ionosphericists and the meteorologists found 
a common interest in the ionosphere from a meteoro- 
logical point of view. The meteorologist with his nose 
to the ground and the ionosphericist with his head above 
the clouds have, since about 1946, permitted themselves 
to recognize the possibility of mutually profitable co- 
operative studies of the high atmosphere. 
Oliver Wulf investigated F-region variations in con- 
nection with upper-air meteorological soundings. The 
Australians studied ionospheric phenomena together 
with movement of fronts across the continent of Aus- 
tralia. Appleton searched for and found a small tidal 
effect in the E-region, and other investigators sought 
connections between the behavior of upper and lower 
portions of the earth’s atmosphere. One of the greatest 
hindrances to appreciation of important variations in 
pressure, temperature, and state of the upper atmos- 
phere has been the concept of an isothermal upper 
atmosphere in diffusive equilibrium. Serious suspicion 
was first cast upon this concept by the Norwegian stu- 
dents of the aurora polaris and by Whipple and his 
colleagues in study of meteor trails. Contemporary 
thought has all but discarded the idea of such a quies- 
cent upper atmosphere. 
Available evidence points towards an ionosphere in 
which thorough mixing of atmospheric gases is the 
rule. Proportions of nitrogen, oxygen, hydrogen, and 
So on, appear to be about the same in the ionosphere as 
at sea level with the exception that the atomic states 
may prevail in the ionosphere at higher levels. The 
amount of water vapor in the ionosphere is thought to 
be negligible. 
From the meteorological standpoit the ionosphere 
appears to have immense possibilities. It is clear that 
energy entering the environment of the earth from 
space first strikes the high atmosphere and at least 
some of this energy causes large changes in the iono- 
sphere. Ionospheric behavior is quite sensitive to varia- 
tions in energy in the ultraviolet light portion of the 
spectrum. The ionosphere probably is influenced to 
a noticeable extent also by corpuscular streams of 
energy. Jones has recently isolated variations in thick- 
ness of the general F-region which correlate inversely 
with ground barometric pressures. While this work is 
incomplete, tentatively it appears that variations in 
ground barometric pressures lag several hours behind 
changes in F-region thickness in some latitudes. 
Ionospheric Temperatures 
Many attempts have been made to deduce, by var- 
ious means, temperatures in the ionosphere. The first 
speculations favored an isothermal condition with tem- 
peratures near 230K. Later when the noon decrease in 
F,-region electron concentration was noted in the North- 
339 
ern Hemisphere, temperatures of the order of 2000K 
were proposed for this region. 
Several approaches have been employed in trying to 
determine ionospheric temperatures. The Norwegians, 
remembering that the aurora polaris occurs in the same 
space as does the ionosphere, have estimated (from 
spectroscopic measurements) nighttime temperatures 
of 228K in the vicinity of 100 km and have argued on 
the basis of similar measurements that this temperature 
increases as soon as the sun’s rays impinge on atmos- 
pheric gases at these heights. Penndorf, using scale 
height of the ionosphere, gives values for the H-region 
temperature near 350K and for the F,-region near 
700K. Other students give values for the E-region rang- 
ing from 100K to 1000K, and for the F-region between 
120K and 4000K. Many of the results have been highly 
speculative and based upon other than conservative 
estimates. 
One of the most promising methods to emerge in 
recent years is deduction of ionospheric temperatures 
on the basis of hour-to-hour changes in data of the 
form of Fig. 2. By means of such data, application of 
the Booker-Seaton method of reduction to true heights, 
use of Appleton’s arguments, and the invoking of Thom- 
son’s relationship between recombination coefficient and 
absolute temperature, it has been possible to make an 
objective approach to this problem. The time rate of 
change of electron density is given by 
dN B 
=o aN, (5) 
where q is the rate of production, and a the recombina- 
tion coefficient between electrons and positive ions. 
The relationship between the recombination coefficient 
and the absolute temperature is given by 
a =ao (Po/P) (T/T), (6) 
where ao, Po, and 7) are reference values of recombina- 
tion coefficient, pressure, and temperature respectively, 
and y probably has a value near 14. Neither of the fore- 
going expressions is exact, but in this simplified form 
they serve to illustrate the central lime of reasoning. 
While the results cannot be considered entirely satis- 
factory, the method has been tested for some twenty 
geographic locations over a range of conditions. In 
most instances results are reasonable and self-consistent. 
One of the unexpected concepts to come from this 
method has been that of a cellular arrangement of 
temperature isopleths, indicating the probability of 
systematic wind systems in the ionosphere. While by 
no means conclusive, application of this objective 
method at the same location and time as soundings by 
rockets gives excellent correspondence at H-region 
heights. 
It is clear from the foregoing discussion that it is no 
longer acceptable to consider the ionospheric temper- 
ature as a simple function of height. Rather it appears 
to be necessary to examine the data from many stations 
over the world throughout the seasons and, from the 
derived information, to construct isopleths descriptive 
of the arrangement of ionospheric temperatures. 
