STRUCTURE OF THE UPPER LAYERS OF THE ATMOSPHERE

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• Document Creation Date: December 22, 2016
• Document Release Date: August 18, 2011
• Sequence Number: 964
• Publication Date: July 20, 1950
• Content Type: REPORT

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SUBJECT Scientific
HOW
PUBLISHED Monograph
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PUBLISHED Moscow
DATE
PUBLISHED 1949
LANGUAGE Russian
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SOURCE Stroyeniye yvsokikh Sloyev Atmosfery, All-Union Society for Dissemina-
tion of Political and Scientific Knowledge.
CLASSIFICATION CONFIDENTI!ffiA'~ O UM 4
CENTRAL INTELLIGENCE AGENCY REPORT
INFORMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS CD NO.
STRUCTURE OF THE UPPER LAYERS OF THE ATMOSPHERE
I. A. Khvostikov
figures are appended_7
ss
meats. Gres progre
Academician A. N. Kolmogorov and his student, Prof A. M. Obukhov, at the Geophys-
ics Institute, Academy of Sciences USSR. In the stratosphere, however, air tem-
perature does not depend upon vertical >9ixing but upon radiation equilibrium.
Any air mass emits radiation, the amount of which is directly proportional to
A. Theory of-the Stratosphere
The stratosphere actually begins with the tropopause. This transitional
region extending one to 3 kilometers between troposphere andosphereiis
distinguished by special temperature conditions, e.g., temperature
height of the tropopause depends on geographical latitude,, being 16-18'kilq.-
meters at the equator and 9-11 kilometers over middle latitudes; it also waxes
seasonally, being maximum in fall and minimum in spring. The stratosphere is,.
colder (minus 70 to minus 80 degrees centigrade) over the equator than over mid-
dle latitudes (minus 45 to minus 55 degrees), and is warmer over the polar re-
gions. The relative positions of stratosphere, tropopause, and troposphere are
shown in Figure 1.
Contemporary theory treats the troposphere as a region where temperature is
regulated mainly by turbulent mixing and the stratosphere as a region in which
it is regulated by radiation heat exchange (radiation equilibrium).. The tem-
perature gradient created by the absorption of reradiation is so grdat that the
transfer of warm air from below into colder higher layers causes powerful ver-
tical movements which equalize the temperature. The expansion cooling of air
in its upward movement creates the temperature gradient (6 degrees centigrade
per kilometer) characteristic of the troposphere. These vertical movements are
turbulent, i.e., small and large air bodies mix with each other in their move-
has been made in the study of atmospheric, turbulence by
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temperature. It also absorbs partially the reradiation passing through it from
the earth's surface and radiation of all circumambient air masses. If the en-
ergy radiated is greater than that absorbed, then the given air mass will con-
tinuously lose its internal energy and will cool or, in the opposite case, heat
up. The stable or equilibrium temperature will be that temperature at which
the energy radiated is equal to the energy absorbed. The mathematical works of
Prof Ye. S. Kuznetsov in the Geophysics Institute, Academy of Sciences USSR, are
of great importance in the development of this theory of radiation equilibrium.
The methods of solving the equations of radiation energy transfer in absorb-
ing and reflecting media devised by the well-known Soviet astrophysicist V. A.
Ambartsumyan (president of the Academy of Sciences Armenian SSR) are highly
promising and have won for him a Stalin Prize. The participation of astrophys-
icists in the solution of such geophysical problems is no accident, for they
use the same theory of radiation equilibrium in studying energy conditions in
stellar atmospheres.
B. Water Vapor in the Stratosphere
The absorption of radiation energy by various gases in the atmosphere re-
veals that the less there is of a given gas in the atmosphere, the greater is
its absorption. To illustrate, we take the five gases always present in air:
nitrogen (78 percent), oxygen (20 percent), water vapor (2 percent), carbon
dioxide (0.02 percent), and ozone (0.00003 percent). Nitrogen absorbs no ra-
diation in the infrared, visible, or ultraviolet regions and consequently has
no effect on energy processes in the atmosphere. Oxygen absorbs radiation but
weakly. The remaining three gases, on the other hand, absorb radiation very
actively. Although ozone has recently been studied in detail, the main empha-
sis has been placed on water vapor throughout almost the entire development of
the theory of the stratosphere. Excessive attention to the study of water va-
por has become a habit which must be broken by geophysicists. Undoubtedly wa-
ter vapor does play a very important role in atmospheric processes. It has
strong infrared absorption bands and absorbs most of the energy reradiated from
the earth, thus influencing greatly the heat balance of the troposphere. Those
who developed the theory of radiation equilibrium in the stratosphere assumed
that water vapor would also be the main absorbing agent in this region. It has
now become clear that the role of water vapor has been overrated and that of
other gases underrated.
The amount of water vapor in the upper troposphere and in the stratosphere
could not be measured accurately until 1946 for two reasons: (1) at low strato-
spheric temperatures the amount of water vapor even in saturated air is infin-
itesimal (fractions of a milligram per cubic meter of air); (2) the water vapor
itself at such low temperatures has complex properties which complicate measure-
ments. Water vapor was considered close to saturation in the upper layers of the
troposphere. Because of the lack of definite data and in order to make calcula-
tions of stratospheric temperatures agree, it was theoretically accepted that
there is so much water vapor even in the stratosphere that it is close to satura-
tion. Only in 1945 and 1946 did reliable methods of measuring water vapor in
the stratosphere become available. The amount of water vapor in the stratosphere
proved to be only one tenth the amount assumed. The water vapor content drops
sharply in the transition from troposphere to stratosphere. There is not nearly
enough water wapor in the stratosphere to maintain by its absorption the tempera-
tures observed there. This does not mean, however, that the theory of radiation
equilibrium as a temperature regulator is incorrect, but that the special role
of water vapor must to a certain degree be transferred to ozone.
C. Ozone in the Stratosphere
It has long been observed that the spectrum of the sun and any star at- the
ultraviolet end is broken at a wave length of about 0.3 micron. Further research
revealed that ozone ib Ltghly absorbing, starting right at the wave length 0.3
micron. But the amount of ozone in the air close to the earth's surface is
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infinitesimal (0.000001 percent), and therefore absorption of light by atmos-
pheric ozone, it would seem, could not entirely cut off the sun's spectrum
around this wave length. However, a much greater amount of ozone might be pres-
ent in the higher atmospheric layers.
When this idea first arose 25 years ago, no airplane or balloon could as-
cend higher than 8 to 10 kilometers, and thus the amount of ozone at great
heights could not be measured directly. However, development of indirect meth-
ods of studying the higher levels began 25 to 30 years ago. These were primar-
ily optical methods, to which later were added acoustic and radio-wave methods.
The study of the higher levels by indirect methods is an outstanding accomplish-
ment of present-day geophysics, and a Soviet scientist, Academician V. G. Fesen-
kov, is a pioneer in this field.
In 1915, Fesenkov published a work in which he showed that the distribu-
tion of air density up to heights of 100 to 200 kilometers could be studied by
measuring the brightness of the sky at twilight. The twilight method has been
widely used in the USSR and abroad in recent years. The method is as follows:
We assume that after the sun goes down the rays come from beneath the horizon
at an angle a; then the earth's shadow in the zenith is equal to h. A short
time later, the angle of submersion of the sun beneath the horizon increases to
al, and the earth's shadow ascends to h'. During this time, therefore, sunlight
has been cut off from the atmospheric layer h' - h, which slightly decreases the
brightness of the sky.
Shortly after the development of the twilight method, other optical methods
of studying the higher atmospheric layers were devised, e.g., by observations
on meteorites and on night-sky luminescence, etc. Then, 15 to 20 years ago,
optical methods of measuring the ozone content up to several score kilometers
by observations from earth were developed.. These measurements showed that most
of the ozone is situated in the higher atmospheric layers, the density being at
a maximum between 22 and 25 kilometers (Figure 2). In every flight of a strato-
spherec'bCd, careful measurements have been made to check this important con-
clusion on the distribution of ozone with height. All lndirre ct measurements in the
Ex-
stratosphere, the latest of which was in 1947, have
Eh
which spectrograph
periments with V-2 rockets in the US in 1946 and 1947, in a
was raised to 88 kilometers, proved that most of the ozone is situated below
40-50 kilometers.
Ozone left to itself will be entirely converted to 02 molecules. The perma-
nent ozone content therefore indicates some regular dissociating factor which
splits 02 molecules into oxygen atoms 0 + 0. Then ozone molecules can be formed
by the collision of 0 atoms with 02 molecules.
This dissociating factor is the ultraviolet radiation of the sun with a
wave length of 0.18 micron or shorter. Here we encounter the important contem-
porary "sun-earth" problem. Many are now working on this problem, one of the most
important in geophysics and astrophysics.
It was recently proved that ozone has such a strong absorption band in the
infrared region around the 10-micron wave length that although the total amount
of ozone in the atmosphere is only 0.00002 of the amount of water vapor, the re-
radiation energy absorbed by ozone is only slightly less than that absorbed by
water vapor. The difference in vertical distribution of these two gases prede-
termines their different roles as temperature regulators of the troposphere and
stratosphere.
There are many reasons to believe that the concept of ozone as a temperature
regulator in the stratosphere will determine the development of the theory of the
stratosphere in the future, but this viewpoint needs checking and development.
What confirms this viewpoint and what needs critical and careful study?
3L
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The point is not solely that there is little water vapor in the strato-
sphere. Since there is a great deal in the troposphere, almost all terrestrial
radiation of those long waves which are absorbed by water vapor remains in the
troposphere. On the other hand, terrestrial radiation of that wave length (10
microns) which is absorbed by ozone passes freely through the troposphere.
One can calculate the equilibrium temperature which an arbitrary gas would
have if it were the only component of air in the stratosphere. For water vapor
it is minus 80 to minus 85 degrees and for ozone it is minus 35 degrees, i.e.,
50 degrees higher. Thus, the higher the ratio of ozone to water vapor, the
higher the air temperature. Since, in the stratosphere, this ratio increases
with height, the temperature also increases. This basic fact could not be ex-
plained by theories which did not take the role of ozone into consideration.
Optical measurements have established that the amount of ozone in the
stratosphere depends on geographical latitude and time of year. The amount de-
creases toward the equator and increases toward the poles, and it is maximum
in spring and minimum in fall. Noting this fact, one can easily explain by ra-
diation equilibrium the decrease in temperature of the stratosphere and the in-
crease in height of the tropopause from the poles to the equator and the sea-
sonal variations in height of the tropopause. Until recently, there was no the-
oretical explanation of these basic facts.
The quantitative side of the new theory is still in need of development,
mainly because of the lack of necessary data on water vapor and ozone content
for various levels. Information on the ozone content is lacking for the most
interesting part of the stratosphere, i.e., the layer from 10 to 20 kilometers.
Systematic data for individual thin layers cannot be obtained by existing
methods, nor can the variation in ozone content be measured in the transition
through the tropopause, although this is of extreme importance. Well-known
specialists in many countries are working to improve the methods for the de-
termination of ozone content. One new method that promises improvement --
searchlight sounding of the atmosphere -- is now being successfully developed
in the Geophysics Institute, Academy of Sciences USSR. In this method, the
powerful beam of a searchlight is directed skyward. By observing afar the beam
at various points with the help of special instruments, one can study the vari-
ous phenomena characterizing the individual atmospheric layers. The Geophysics
Institute has made considerable progress in this direction, having conducted
such optical sounding of the atmosphere up to heights of 55 kilometers. At any
rate, the theory of the stratosphere will be advanced considerably after more
accurate data is obtained on the vertical distribution of water vapor and ozone
around heights of 14 to 18 kilometers.
D. Temperature of the Higher Atmosphere Layer
Soviet rasonde measurements, which have reached 25-30 kilometers, indicate
a slight increase in stratosphere temperature with height. In the past decade,
however, important results obtained by indirect methods indicate that special
temperature conditions prevail in the higher levels. These may briefly be char-
acterized by the rule, "the higher, the hotter." We will first consider acoustic
data.
In World War I it was observed that sometimes a heavy artillery barrage
could be heard at great distances but with regions of silence. Later, the "anom-
alous zones of audibility" were established by acoustic measurements in heavy
explosions. Normal audibility disappears at a distance of 30-50 kilometers. A
region of silence follows, and then still further from the point of explosion
the sound is heard again (Figure 3). It has been theoretically proved that the
sound waves are refracted from air layers 35 to 60 kilometers high. The sound
waves can be refracted back to earth if the air temperature (upon which the ve-
locity of sound waves depends) in the return layers increases with height. The
phenomena observed can be explained if we assume that the air temperature
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increases rapidly with height from 25-30 kilometers to 50 kilometers, e.g., 30
degrees at.40 kilometers, about 60 degrees at 50 kilometers, and 75 degrees at
60 kilometers (Figure 4). fon the assumption of a uniform increase of tempera-
ture with altitude setting in at about 30 kilometers, Whipple calculated the
temperatures necessary to account for the transit times of the sound and the
angles of the downcoming rays as observed during daylight hours of the months
from May to September in the years 1928 - 1930. The temperatures came out
around 7 degrees at 40 kilometers and 77 degrees at 55 kilometers. -- Terres-
trial Magnetism and Electricity, edited by J. A. Fleming, McGraw-Hill, New York,
1939, reprinted 194% p 501
The steady increase in temperature with height in these layers is confirmed
by twilight observations. Since the density of air in the levels from 20-30 to
150-250 kilometers can be found by this method, temperature and pressure distri-
butions can also be calculated. This method has been used extensively in Ger-
many, the US, Britain, France, and other countries. Even today, however, Soviet
scientists lead in this method because of the theoretical and basic experimental
work of the Abastumyan Astrophysical Observatory, Academy of Sciences Georgian
SSR, and the Geophysics Institute of the Academy of Sciences USSR. In 1946,
the density of air up to heights of 250 kilometers was determined from measure-
ments at the Abastumyan Observatory. From these densities, the air temperatures
were calculated; at 200 kilometers, the temperature was calculated to be 600 de-
grees.
Thus, the opinion, held until recently, that the upper layers of the atmos-
phere are very cold is now refuted. Interesting results have been obtained by
observations on the luminescence of meteors. Simultaneous photography of meteors
from two points permits one to determine the height, speed, and brightness of
the meteor for various points of its trajectory. The values of air density ob-
tained by this method agree well with those obtained by twilight observations.
For the past 6 to 8 years, a number of determinations of air density have
been made with the help of reflected radio waves. All these methods taken to-
gether permit one to construct an approximate picture of the temperature of the
upper stratosphere. (Figure 5). Above 60 kilometers the temperature begins to
drop and reaches a minimum at 80 kilometers. Above 80 kilometers the tempera-
ture begins to increase rapidly again, and this increase continues to 200 kilo-
meters. But above 100 kilometers we enter a special region of the atmosphere,
the ionosphere.
E. Composition of Air in the Ionosphere and the Problem of Vertical Mixing
The ionosphere is divided into the following layers: the E-region at 100
kilometers and the F-region at 250-300 kilometers; the latter is sometimes sub-
divided into the F1- and F2- regions. There is also the weakly reflecting
D-region at 50 to 70 kilometers, which operates only on the longest (kilometer)
wave lengths.
The chemical composition of air in the levelr,.above 100 kilometers can be
determined by studying the spectrum of the northern lights and the luminescence
of the night sky. Photographing the northern lights simultaneously from two
points 10 to 50 kilometers apart permits determination of their height. This
method showed that the lower edge of the northern lights never drops below 100
kilometers j On interesting case of an auroral arc with,a red lower border was
measured at the Auroral Observatory at Tromso in 1932 by Harang and Bauer. They
found the are descended to an altitude of 65 to 70 kilometers. This is the low-
est height as yet measured by the photographic method." -- J. A. Fleming, Op.
Cit., p 5877. The upper edge extends to 250-400 kilometers and in rare cases to
800-1,000 kilometers. In the laboratory, the chemical composition of a gas can
be determined by passing an electrical discharge through the gas and studying
the spectrum given off by the gas. The northern lights, in the same way, are
just luminescence caused by an electrical discharge in the air. Thus, the air
composition up to 100 kilometers can be determined by a study of the spectra of
the northern lights.
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Another interesting natural phenomenon, called night-sky luminescence, was
discovered some 30 years ago. The brightness of the night sky on a clear moon-
less night, as shown by measurements and calculations, is two or three times
"greater than necessary," i.e., greater than can be explained by the light of
all stars. It was proved that the higher atmospheric levels, mainly the level
from 130 to 180 kilometers, shine continuously. Study of the spectra of this
luminescence, the nature of which is still not completely clear, permits one to
determine the composition of the upper levels of the atmosphere over any part
of the world, and not just over polar regions, as in the case of the northern
lights. Studies showed that the air composition even in the highest levels was
the same (nitrogen-oxygen) as that prevailing in the lower levels. This result
was unexpected, since it had previously been considered from the fundamental
principle of hydrostatics (which yields the well-known "barometric" formula)
that light gases must predominate in the higher levels and that therefore the
ionosphere must be almost completely hydrogen. Now it has been proved that hy-
drogen does not exist in the stratosphere and ionosphere, at least not as a
permanent and noticeable component. Thus, the atmosphere is "mixed" at all
heights. This result is not surprising since, according to the stratosphere
theory previously discussed, there is no vertical mixing in it, i.e., the
stratosphere is a region of stable vertical equilibrium.
The problem of a "mixed" atmosphere is one of the most important in present-
day geophysics. Complex analyses of air samples taken from various levels up
almost to 29 kilometers have recently been undertaken in various parts of the
world. The studies have been concentrated on the content of oxygen and helium.
The oxygen content up to 20 kilometers is strictly constant, i.e., 20.9 percent
by volume. There is a slight decrease in the oxygen content above 20 kilometers,
reaching 20.4 percent at 282 kilometers (Figure 6). There is 0.00052 percent
helium at the earth's surface, and 0.00054 percent at 25 kilometers. Geophysi-
cists must explain the mechanism of vertical mixing of air in the stratosphere
and ionosphere. The temperature criterion of vertical stability of the strato-
sphere is of course incomplete. Horizontal air movements must be taken into
consideration, especially since, as we shall see below, there are permanent
high-speed air flows in the stratosphere and ionosphere.
F. The Ionosphere and the Sun
The spectra of the northern lights and the luminescence of the night sky
show that oxygen is completely dissociated in the ionosphere. In the past 3 to
5 years, evidence has appeared on the partial dissociation of nitrogen, but this
question is still under discussion.
The agent that supports permanent dissociation and ionization of air in the
ionosphere is solar radiation. When sunspots increase, ionization of the upper
layers is intensified, accompanied by disturbance of radio communication, mag-
netic storms, and especially bright northern lights. But what is the radiation
of the sun that produces ionization and dissociation; is it ultraviolet or cor-
puscular? Many are working on this very important problem of present-day astro-
physics and geophysics. There is evidence for both types of radiation.
Several eclipses have been used for observations with the help of radio
waves on ionization variations during optical and corpuscular eclipses. The ac-
tive effect of ultraviolet radiation upon the F-region (10-20 percent decrease
in ionization during optical eclipse) was established beyond question. The in-
fluence of a particle (corpuscular) eclipse was not observed. The observations
of Ya. L. Alpert an article by Al'pert,?"The Structure of the Atmosphere and
the Processes in the Region of the F-Layer" appeared in Zhurnal Eks rimental'-
no i Teoreticheski Fiziki Vol I No 11 Nov 1948;
a . N. Goroz ankin near Moscow during the 9 July 1945 eclipse per-
m e some conclusions on the influence'of solar corpuscular streams with veloc-
ities of 400-600 kilometers per second and higher. A number of observations with
the newest equipment during future solar eclipses are still necessary to clear up
all essential facts on the dissociating and ionizing action of solar radiation on
the ionosphere.
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G. Wind in the Stratosphere
The study of air currents in the upper layers of the atmosphere is a prob-
lem of great practical and theoretical importance. The development of a theory
of general atmospheric circulation, the principles of the general study of move-
ments of the atmosphere and the theoretical basis of weather forecasts, and de-
mands of long-range artillery, rocket aviation, and acoustic reconnaissance all
require information on the speed and direction of air movements at various
heights and at various points of the globe, dependent on the time of day and
season. Geophysics still lacks the required data, and it is urgent that it be
obtained.
First in the methods of studying winds in the stratosphere are observa-
tions on noctilucent clouds. These clouds are sometimes visible after sunset
and before sunrise. It has been established that noctilucent clouds are always
located at an almost constant height, i.e., 80-83 kilometers. This constancy
of height is apparently connected with the presence of a permanent powerful
temperature inversion which begins right at this level. These clouds move rap-
idly, and their speed can be measured by photography. Second are meteor trains,
which permit determination of the speed and direction of wind at various heights.
Some information on the movement of "clouds" of high ion concentration in the
ionosphere has recently been obtained by radio observations.
Important information on this problem may also be obtained by acoustic
measurements of the zones of anomalous audibility in powerful explosions. This
method has not received the development which it deserves. Soviet geophysi-
cists (Prof S. V. Chibisov and others) are credited with the best theory on
this complex phenomenon.
Finally, in 1946, an Englishman made a number of observations on the drift
of smoke formations from special smoke chambers fired from a zenith cannon up
to heights of 30 kilometers. The presence of powerful and regular air currents
at various atmospheric levels was established. A typical representation, in
which some data is collated, is shown in Figure 7.
Wind velocity in the troposphere increases with height, reaching a maximum
of 20 to 25 meters per second beneath the tropopause. At this height, moreover,
the winds have a prevailing direction. In the stratosphere, the wind velocity
begins to decrease rapidly with height, reaching a minimum of 6 to 8 meters per
second at 19 to 22 kilometers. In the higher layers, however, an exceedingly
rapid intensification of winds is observed. The wind velocity approaches 70
meters per second at 40 kilometers, and 140 meters per second at 60 kilometers.
The powerful temperature inversion beginning at 80 kilometers may possibly play
the role of a "second tropopause" in certain respects. In any case, the wind
velocity apparently reaches its maximum (up to 160 meters per second) here and
decreases in the higher levels.
The prevailing wind direction in the "second tropopause" is directly oppo-
site to the wind direction in the tropopause proper. It is possible that these
two tropopauses constitute an important element of a closed circulation system
in the stratosphere, and that the much greater velocities in the upper tropo-
pause are necessary according to mass balance or conservation of mass (since
the air density decreases with height).
Appended figures follow]
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