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OCR for page 141
The Medical Implications of Nuclear War, Institute of
Medicine. ~ 1986 by the National Academy of Sciences.
National Academy Press, Washington, D.C.
Atmospheric Perturbations of
Large-Scale Nuclear War
ROBERT C. MALONE, PH.D.
Los Alamos National Laboratory, Los Alamos, New Mexico
Several of the papers in this volume have discussed nuclear winter,
large fires, and the dynamics of smoke plumes from large hires. I would
like to elaborate on this theme by describing new computer simulations
of the atmospheric consequences of the injection of a large quantity of
smoke. I will focus on what might happen to the smoke after it enters the
atmosphere and what changes or perturbations could be induced in the
atmospheric structure and circulation by the presence of a large quantity
of smoke.
To help in understanding the significance of these atmospheric pertur-
bations and the manner in which they anse, I will start by breaking the
nuclear winter phenomenon into its component parts. A very simplified
view of nuclear winter is represented in Figure 1A, in which is shown a
vertical column of processes and a box to the side that represents smoke
injected into the atmosphere. Ignoring the rest of Figure 1 for the moment,
it can be seen that there are two basic ingredients to nuclear winter: sunlight
coming into the earth's atmosphere and smoke that has been injected into
the atmosphere by fires. The smoke absorbs some of the incoming sunlight,
causing a reduction in sunlight reaching the earth's surface. A radiation
The material on which this presentation is based is drawn from two papers (Malone et
al., 1985, 1986). Readers interested in a more comprehensive discussion that includes
historical background, related research, technical details of the model, and more extensive
references should consult these articles, particularly the latter.
All figures are reprinted from Malone, R. C., et al., 1986, Nuclear winter: three-
dimensional simulations including interactive transport, scavenging, and solar heating of
smoke, J. Geophys. Res. 91 (D1): 1039-1053, @) 1986 by the American Geophysical Union.
Reprinted with permission.
141
OCR for page 142
142
PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES
deficit at the surface results because the surface continues to emit infrared
radiation (heat). The smoke particles do not trap infrared radiation effec-
tively, so the heat goes out into space (not indicated in Figure 11. This
continuing heat loss to space combined with reduced incoming sunlight
causes the surface to cool. This is the origin of the so-called nuclear winter
effect.
It is apparent Mat the magnitude of the cooling would depend on the
amount of smoke injected and that the duration of the cooling would
depend on how long smoke remained in the atmosphere.
The latter point brings us to the next element of complication in this
picture, which is the removal of smoke from the atmosphere by rainfall
(Figure 1B). Precipitation scavenging of smoke, as this is also called, was
considered in the TTAPS study of nuclear winter (Turco et al., 1983) and
~ r -A ,
I ~ SUNLIGHT I ,
1
~ , ~
SURFACE
COOLING
ABSORPTION
BY SMOKE
HEATING
~OF SMOKE
l l .
I ! WINDS
~ I
SMOKE LOFTING
LOWERING OF
TROPOPAUSE
| ATTENUATION |
OF SUNLIGHT
.
,. . 1
DISTRIBUTION
AMOUNT OF
SMOKE
I, B
A |
.________________J
FIGURE 1 Interconnection of the processes which control the distribution and res-
idence time of smoke in the atmosphere and the resulting surface climatic change.
Some arrows indicate that one process causes another; other arrows indicate only that
a process influences the operation of the process to which the arrow points. For
example, the presence of smoke in the atmosphere results in the absorption of sunlight,
which causes heating, which causes both lofting of the smoke and lowering of the
tropopause. These two effects influence (decrease) the efficiency with which precip-
itation removes smoke by changing the vertical distribution of both smoke and pre-
cipitation. Removal by rain changes the amount of smoke. Heating also modifies the
winds, which influence the distribution of smoke. Source: Malone et al. (1986, p.
1040).
OCR for page 143
ATMOSPHERIC PERTURBATIONS OF GE-SC NUCLEI Wow 143
also in the report on this subject by the National Academy of Sciences
(1985~. However, with the models that were available at the time, it was
necessary to assume that the removal of smoke by rainfall occurred at a
rate that was prescribed based on the observed lifetime of smoke particles
in the unperturbed atmosphere. Although it was recognized that changes
in the atmosphere would occur, it was not possible to take these changes
into account in the models.
It has now become possible to investigate these atmospheric changes
with more complicated models that have been developed in the last few
years. These changes are quite important because they influence the ability
of precipitation to remove smoke from the atmosphere and, therefore, the
duration of the climatic effects of smoke. Now the last elements can be
added to the diagram (Figure 1C). The principal ingredient in Figure 1C
is heating of smoke-filled air due to absorption of sunlight by smoke
particles. This heating causes changes in the atmospheric circulation and
structure (also indicated in Figure 1C) the atmospheric perturbations
alluded to in the title of this paper.
The first of these perturbations is a major change in the atmospheric
circulation patterns that causes the heated air and the entrained smoke
particles to rise. This carries some smoke particles well above the altitudes
to which they were injected initially by the fires. The second change is
one that takes place in the vertical thermal structure of the atmosphere,
which is also brought about by the heating of smoke-filled air. As I will
show in this paper, both of these effects inhibit the ability of the atmosphere
to purge itself of smoke. Specifically, they reduce the efficiency of smoke
removal by precipitation.
In fact, there is a competition between rainfall, which removes smoke
from the atmosphere, and these atmospheric perturbations, which act to
isolate smoke from removal by rainfall. Precipitation scavenging begins
to act as soon as smoke is injected into the atmosphere. In the model
calculations, precipitation is able to remove a substantial amount of smoke
during the first two weeks. During that time these perturbations develop
and, at least for summertime conditions and large smoke injections, can
become dominant.
These changes in the atmospheric structure and circulation are important
in their own right, but it should be noted that they form a feedback loop
in which elements of Figures 1A, 1B, and 1C are interconnected. In the
full diagram, the amount (and spatial distribution) of smoke remaining in
the atmosphere at any time is influenced by the changes caused by solar
heating of the smoke itself. In a given season of the year, the intensity
of heating depends on the amount (concentration) of smoke. Consequently,
if larger injections of smoke are postulated, stronger heating results and
causes larger atmospheric perturbations and greater inhibition of smoke
OCR for page 144
44
PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES
removal by rain. Thus, the larger the amount of smoke injected, the greater
is its ability to modify the atmosphere and, thereby, to inhibit its own
removal. (For very large smoke injections, another effect, discussed by
Malone et al. [1986], modifies this conclusion.) For a given amount of
injected smoke, the intensity of heating depends on the amount of sunlight
that is available. Assuming that smoke would be initially injected only in
the Northern Hemisphere, the heating of smoke and the resultant atmos-
pheric perturbations would be greater in July than in January, simply
because there is more sunlight in the Northern Hemisphere in July than
in January.
The computer model that we used for our studies is a general circulation
model or global climate model, or simply a GCM. It is a three-dimensional
model that solves on a computer the mathematical equations describing
the evolution in time of the winds, temperature, moisture, and other
quantities throughout the earth's global atmosphere.
To study the nuclear winter problem, the capability of transporting
aerosols (very small particles) with the simulated winds of the model was
added. The model's solar radiation scheme was modified to allow for the
absorption by smoke particles of sunlight coming into the atmosphere. A
very simplified treatment of the removal of smoke from the atmosphere
by rainfall was also added. For this rainfall was used as predicted by the
model itself, so that changes in rainfall caused by the heat-induced at-
mospheric perturbations could be taken into account.
In the computer simulation studies that I will describe, smoke was
injected into the model atmosphere over the United States, Europe, and
the western part of the Soviet Union. The injection rate decreased linearly
to zero at day 7. Half of the smoke was injected during the first two days.
The sensitivity of smoke transport and removal to the assumed initial
vertical distribution of smoke was considered by using two profiles: a low
injection with smoke distributed between 2- and 5-km altitude in the lower
troposphere, and an NAS injection (so-called because of its use in the
study done by the National Academy of Sciences) with constant smoke
mass density between the surface and a 9-km altitude (NAS, 1985) but
still within the unperturbed troposphere. Both January and July conditions
were used to reveal seasonal differences. The behavior of aerosols in the
normal atmosphere was studied with a passive tracer which, like smoke,
is transported by the model's winds and removed by the predicted rainfall
but, unlike smoke, does not absorb sunlight. This last characteristic permits
the model atmosphere to evolve unperturbed by the presence of the passive
tracer. The contrasting behaviors of interactive smoke and passive tracer
illustrate clearly the importance of atmospheric heating due to sunlight
absorbed by smoke particles.
The amount of smoke that is assumed to be injected into the atmosphere
OCR for page 145
ATMOSPHERIC PERTURBATIONS OF LARGE-SCALE NUCLEAR WAR 145
is an important parameter, but estimates of this quantity are quite uncertain.
The study by the National Academy of Sciences (NAS, 1985) estimated
a range from 20 teragrams (Tg; 1 Tg = 1012 grams = 1 million metric
tons) up to as much as 640 Tg of smoke. I will present only results for
170 Tg, a value close to the NAS baseline value; results for other smoke
amounts can be found in Malone et al. (19861.
Now I would like to explain more fully some of the elements of Figure
1. Using July conditions, because the atmospheric changes are larger and
more easily seen, I will first describe smoke lofting and then show how
the structure of the atmosphere is changed. Next I will describe how these
effects influence the removal of smoke by rainfall and the lifetime of
smoke in the atmosphere. Finally, I will describe briefly the findings about
the climatic impact of smoke.
Figure 2 contains a comparison of two calculations that illustrate nicely
the influence of solar heating on the dynamics of smoke. One calculation
was done with interactive smoke; the results from it are shown with solid
contours. The second calculation was done with a passive tracer; its results
-
30
25
20
it,
15
10
5
to
' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
DAY 20
_ rlO
.1,: ~
UP 60 30 ED -30
-60 SP
LA TITUDE
10
20
30 _`
~2
50
70
100 ~
CO
200
300
500
700
1000
FIGURE 2 Longitudinally averaged mass mixing ratios for July conditions at
day 20. The dashed contours apply to a passive tracer, while the solid contours
apply to interactive smoke. In each case 170 Tg (1 Tg = 1012 g = 1 million
metric tons) of material was injected over the Northern Hemisphere continents
with a low injection profile (see text). The contours of mixing ratio are labeled
in units of 10-9 g material/g air. Source: Malone et al. (1986, p. 1044~.
OCR for page 146
146
PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES
are shown with dashed contours. In both calculations the same amount of
material (170 Tg) was injected over the Northern Hemisphere continents
in July at altitudes between 2 and 5 km (low injections). The contours
indicate the concentrations of material (in parts per billion by mass) re-
maining at day 20 in the calculations, averaged over all longitudes. The
display extends from the North Pole to the South Pole and from the surface
of the earth up to about 30 km, which is in the lower stratosphere. (I will
explain a little more about the normal atmospheric structure in connection
with Figure 3.) These contours tell us how much of the material is left at
day 20 and how it is distributed over latitude and altitude.
Most of the passive tracer remains at low altitudes, where it was injected,
because the passive tracer and surrounding air are not heated by sunlight.
Since scavenging by rainfall is fastest in the lower atmosphere, the passive
tracer is rapidly removed, as indicated by the relatively small concentra-
tions (Figure 21.
In the interactive case, on the other hand, the smoke does absorb sun-
light. The heating drives vertical motions that carry smoke-filled air up-
ward from the region of injection in the lower atmosphere. This takes
some smoke up higher, completely out of reach of removal by precipi-
tation. Also, the heating of the atmosphere inhibits the formation of pre-
cipitation. This allows more smoke to remain, as can be seen by the larger
concentrations on the solid contours.
Before showing how the structure of the atmosphere is changed by the
heated smoke, let me first describe the atmosphere as it normally exists.
Figure 3A displays the longitudinally averaged temperature in the atmos-
phere for normal July conditions. The temperature contours are labeled
in degrees Kelvin (273°K = 0°C). The structure of the atmosphere in its
normal state is such that the temperature is warmest at the surface and
decreases upward with height to an altitude of about 10 km. This region
is called the troposphere. At about 10-15 km, the temperature becomes
relatively constant with height and then increases with height in the strat-
osphere because of the absorption of sunlight by ozone. The heavy dashed
line in Figure 3A shows the approximate position of what is called the
tropopause, which is the boundary between the troposphere and the strat-
osphere.
For the purpose of this study, the most important characteristic of the
troposphere is that it is the region of the atmosphere in which storms and
rainfall occur. Since precipitation is the primary removal mechanism for
smoke, this is where smoke removal will take place.
Figure 3B also displays the longitudinally averaged temperature for July
conditions, but with the atmosphere being perturbed by the injection of
170 Tg of smoke. The smoke was injected with constant density from the
surface up to about 9 km (NAS injection), so that all of it is in the
OCR for page 147
ATMOSPHERIC PERTURBATIONS OF LARGE-SCALE NUCl FAR WAR 147
A
30
1 1 1 1 1 1 1 1 1 11 1 1 1
(
25
23° ~210
^20 _ ~
15 I)
10
5
.
O
B
30
;S, 20
n
15
A: 10
r
'10
__ ) )
1~1 1 ~: )
NP 60 30 ED -30 -60 SP
20
30 ._`
50 `§
70
100
200
300
500
700
1000
~70 \
_ 330~ )
- t'---4270~q
o
30 ED -30 -60 SP
LA TITUDE
20
30 ~
50 `§
70
100 ~
co
co
200
300
500
700
1000
FIGURE 3 The longitudinally averaged temperature (degrees Kelvin) in the simulated
unperturbed (A) and perturbed (B) atmospheres for July conditions. The perturbed
distribution in (B) is a 5-day average beginning 15 days after the initiation of injection
of 170 Tg of smoke with the NAS vertical injection profile. The unperturbed distri-
bution in (A) is a long-term average. In each figure the approximate position of the
tropopause is indicated by a heavy dashed line. Source: Malone et al. (1986, p. 10451.
OCR for page 148
48
PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES
unperturbed troposphere and is initially subject to removal by rainfall.
The heating by sunlight of this smoke, some of which is carried higher
(Figure 2), is quite intense and changes the vertical thermal structure of
the atmosphere significantly. Figure 3B shows a S-day average of the
temperature during the third week after smoke injection began. There is
still a region in the lower atmosphere in which temperature decreases with
height; that is, there is still a troposphere. However, the top of the tro-
posphere is now at about 5 km, rather than at 10-12 km as in the normal
atmosphere.
Higher up the solar heating of smoke has raised the temperatures by as
much as 50-80°K above normal. A situation now exists in which the
smoke has created its own "stratosphere." Above the lowered tropopause
[heavy dashed line in Figure 3B], warm air overlies cooler air, a condition
that inhibits convective motions that would bring about precipitation.
Consequently, precipitation is confined below the tropopause and most
of the remaining smoke is above it, as illustrated in Figure 4. The heavy
dashed line, taken from Figure 3B, again represents the tropopause, the
boundary between the troposphere and the heated region. The cross-hatch-
ing shows where precipitation is occurring; clearly, it is confined below
the tropopause. The black stippling, which indicates various concentra-
tions of smoke, shows that smoke now resides primarily above the tro-
popause. Smoke that was below the lowered tropopause largely has been
removed by precipitation. Because the remaining smoke is now separated
physically from its primary removal mechanism, its lifetime in the at-
mosphere is greatly increased.
This increased lifetime can be seen in Figure 5, which shows the tem-
poral evolution of the total mass of material remaining in the atmosphere.
The upper four curves apply to interactive smoke calculations with vertical
injection profiles, as indicated, while the lower pair of curves apply to
passive tracer calculations with low injection profiles. The vertical axis
has a logarithmic scale. The total injection in all of these cases was 170
Tg, a value that is near the top of the diagram. As a result of scavenging
by rainfall, none of the curves ever reaches the 170-Tg level. A substantial
amount of material is removed while the injection proceeds.
The passive tracer curves in Figure 5 approximately represent normal
aerosols in the unperturbed atmosphere. Following the cessation of injec-
tion at day 7, these curves fall in almost straight lines, which means that
material is removed exponentially in time. These two curves provide a
useful validation of our model. They tell us that aerosols in the normal
atmosphere, as calculated by the model, have a residence time on the
order of one week. This is in good agreement with observations.
Now, contrast that with the behavior of interactive smoke indicated for
July by the upper pair of dashed curves. During the first week or two, a
OCR for page 149
ATMOSPHERIC PERTURBATIONS OF ~GE-SC~ NUCLEI Wit 149
- ~ ~ I: l::::! ~:l::.:::l::.::.:::l.: :l :! in I I I I I I
OAYS 15-20
25
20
C)
15
10
5
o
Ad..
...~/////////5~////~
.. : : : : At/ / / / / 7 / / ~ -
-~d~
UP 60 30 ED -30 -60 so
LA TITUDE
10
20
30 _
50
70
100 ~
CO
200
300
500
700
1000
FIGURE 4 The relative positions of the modified tropopause (heavy dashed line)
and the precipitation distribution (cross-hatched region below the tropopause),
both averaged over days 15-20, and the smoke distribution at day 20 (stippled area
above the tropopause) for the 170-Tg NAS case portrayed in Figure 3B. Darker
stippling indicates greater smoke loading; the smoke contour intervals correspond to
mixing ratios of to x 10-9, 40 x 10-9, and 70 x 10~9 g smoke/g air. These
can be compared win We solid contours in Figure 2, which apply to a low injection
July case, also at day 20. Source: Malone et al. (1986, p. 10451.
substantial amount of smoke has been removed from the atmosphere. This
is mostly smoke down low that can be easily removed by rain. But because
there is strong solar heating in the Northern Hemisphere in July, the rate
of removal of smoke is greatly decreased after the first two weeks. As
explained above, this occurs because some smoke has been carried higher
in the atmosphere and because the atmospheric structure has been mod-
if~ed. Approximately one-third of the mass of smoke initially injected still
remains in the model atmosphere after 40 days of the July calculations.
This smoke has a very long lifetime in the atmosphere, as indicated by
the near constancy after day 15 of the upper pair of dashed curves in
Figure 5.
Up to this point, I have only talked about July because it is easier to
illustrate the interesting effects for July conditions than for January. The
upper pair of solid curves in Figure 5 show the interactive smoke results
OCR for page 150
50
100
CO
O 10
CO
o
1
PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES
l
_ JANUARY
JUL Y
0 5
NAS LOW_
-'~PASSIVE, LOW
10 ~-0
TIME (DA YS)
FIGURE 5 The mass of material remaining in the global atmosphere as a function
of time. The upper four curves apply to smoke; the lower pair apply to the passive
Lacer. Solid and dashed curves indicate January and July conditions, respectively.
Labels indicate low and NAS injections. The slopes of the passive Lacer curves
at late times yield 1/e-residence times of 5 to 6 days, which agree well with
observed residence times of aerosols in the lower troposphere. Source: Malone
et al. (1986, p. 10461.
for January. Smoke is removed faster in January than in July simply
because there is less sunlight in the Northern Hemisphere to drive the
atmospheric perturbations that enhance the lifetime of smoke. By the end
of six weeks in our January calculations, the remaining fraction of smoke
injected with the low and NAS profiles is about 5 and 15 percent, re-
spectively, compared with 35 percent in the July cases. Nevertheless,
solar heating of smoke does have a significant effect even under winter
conditions. After three weeks, there is approximately a factor of three
more smoke present in the atmosphere in January than would have been
the case without the influence of solar heating (compare the passive tracer
curve). In July the comparable ratio of smoke to passive tracer mass is
about 10 after 3 weeks.
Figure 6 consists of two maps of the world showing the distribution of
smoke looking down through the atmosphere at days 20 and 40. Most of
the smoke is still concentrated in the Northern Hemisphere. Transport of
smoke by the winds has made the geographical distribution of smoke fairly
OCR for page 151
ATMOSPHERIC PERTU~ATIONS OF ~GE-SC~E NUCLEI Wow
A
90
60
o
-30
-60
_ Ott
-90 II ~I··I.,I I,,I
-180 -150 -120 -90 -60 -30 0 30
DAY 20
-¢-~0.1~ ~J
1 _! I . . I . , , .
60 90
B
60
30
o
-60
120 150 180
DAY 40
r ~
...... ; ., 1,, 1, I
_90 ~ I I I I I I .
-180 -150 -120 -90 -60 -30
, I,, I ., 1,, I . . I . . I
0 30 60 90 120 150 180
FIGURE 6 The vertically integrated solar absorption optical depth of smoke at
day 20 (A) and day 40 (B) of the interactive July simulation with 170 Tg injected
with the NAS vertical profile. The contours are presented at intervals of 0.1, with
the lowest value being 0.1 on the southernmost contour. If ~ is the absorption
optical depth, the light reaching the surface from the sun overhead is reduced by
a factor of e-T. For ~ = 0.1, 0.3, 0.5, and 0.7, the factor e-T is 0.90, 0.74,
0.61, and 0.50, respectively. Source: Malone et al. (1986, p. 1047~.
OCR for page 152
152
PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES
uniform in longitude, although some nonuniforrnities remain. Some low-
level smoke lingers over the continents. This is possible because the
surface cooling (Figure 7) causes evaporation and precipitation to decrease
over the continents. Air over the oceans is clearer. Some smoke has
reached the Southern Hemisphere. The quantity displayed in Figure 6 is
called the absorption optical depth and can be used to determine the
attenuation at the surface of sunlight coming down through the atmosphere.
The fractional attenuation is about 10, 25, 40, and 50 percent for optical
depths of 0.1, 0.3, 0.5, and 0.7, respectively.
Figure 7 shows the changes in surface air temperature, relative to nor-
mal, predicted by the model when 170 Tg of smoke is injected in July.
A 5-day average of the temperature change near the end of the first week
is displayed in Figure 7A. It shows cooling by 15°C or more over large
areas of the interiors of the North American and Eurasian continents during
this period when the smoke clouds are particularly dense over the regions
of injection. The long lifetime of smoke under summer conditions causes
significant reductions in the surface air temperature to last through the
end of the calculation at day 40. Figure 7B shows the simulated temper-
ature changes during week 6; reductions of 5-15°C persist over the north-
ern midlatitude continents. The features in the Southern Hemisphere have
nothing to do with what is going on in the Northern Hemisphere; they are
due simply to normal weather fluctuations in the winter (Southern) Hemi-
sphere.
For 170 Tg of smoke injected in January, simulated surface air tem-
perature reductions of 5-15°C occur over portions of the northern mid-
latitude continents during the first few weeks. However, the faster removal
of smoke allows the temperatures to recover toward normal more rapidly
than in July.
The discussion so far has focused on a baseline value of 170 Tg of
injected smoke. However, it was pointed out in connection with Figure
1 that the intensity of heating, the magnitude of the atmospheric pertur-
bations, and the smoke removal rate all depend on the concentration
(hence, total mass) of injected smoke. A very small amount of smoke has
little impact on the atmosphere, which allows the smoke to be quickly
removed from the troposphere, much like the passive tracer results in
Figures 2 and 5. As the injected mass is increased in the simulations into
the range estimated for a major nuclear exchange, the solar heating of
smoke and the atmospheric perturbations increase in magnitude. The frac-
tional mass remaining in the atmosphere at late times also increases, and
its rate of removal decreases. This trend continues up to injected masses
comparable to the baseline value (170 Tg). With still larger values, another
effect comes into play that causes the fractional mass remaining to stop
increasing and even to decrease somewhat (Malone et al., 19861.
OCR for page 153
ATMOSPHERIC PERTURBATIONS OF ~GE-SC~E NUCLEI Wit 153
A
9o 1
30
-30 _
-60
B
60
30
n
-30 _
-on _
DAYS 5- 10
I 1 1 ~I ~ 1 1 1 ~1 1 _ _ .
- L~
-90
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
~ ~Do ~;~ a
MOO ~) _
to or
-5to-15 t ~>+5~/~
DAYS 35 - 40
· '~::
L~
-90
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
-5 to -15 it ~ >~ '1 ~ + 5 //
FIGURE 7 The change in surface air temperature relative to the unperturbed
atmosphere in July for 170 Tg of smoke injected with the NAS profile. Five-day
averages of the perturbed case, minus the long-term average of the unperturbed
case, are shown: (A) days 5-10, (B) days 35-40. Only changes larger in mag-
nitude than 5°C are shown. Values are indicated at the bottom of the figure; the
designation <-15 refers to temperature reductions below normal in excess of
15°C. Note that the warm and cool regions near Antarctica are simply manifes-
tations of storms which occur naturally in the wintertime circumpolar flow; they
have no connection with the changes occurring in the Northern Hemisphere.
Source: Malone et al. (1986, p. 1049~.
OCR for page 154
154
PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES
In summary, solar heating of smoke is a very important factor. It
produces two effects. One is that some smoke is carried well above its
initial injection height. The second is a modification of the atmospheric
structure in which heating pushes the tropopause downward. Both effects
contribute to isolation of smoke above the tropopause from precipitation
below and cause an increase in the lifetime of that smoke relative to what
one would find if solar heating of smoke were neglected. The magnitude
of these effects depends on the season of year and the amount of smoke
injected into the atmosphere by fires.
There would be substantial cooling of the Northern Hemisphere con-
tinents during the first few weeks in both January and July. In the July
case only, the prolonged lifetime of smoke suggests that significant tem-
perature reductions could persist for many weeks. Smoke would spread
into the Southern Hemisphere in July as a result of the strong circulations
driven by the solar heating of smoke. There would be very little spread
into the Southern Hemisphere for January conditions; the smoke simply
is not heated enough and is removed too fast.
Interested readers should consult the paper of Malone et al. (1986) for
a more complete discussion that includes the simulated surface climate
impact of various smoke amounts.
REFERENCES
Malone, R. C., L. H. Auer, G. A. Glatzmaier, M. C. Wood, and O. B. Toon. 1985.
Influence of solar heating and precipitation scavenging on the simulated lifetime of post-
nuclear war smoke. Science 230:317-319.
Malone, R. C., L. H. Auer, G. A. Glatzmaier, M. C. Wood, and O. B. Toon. 1986.
Nuclear winter: Three-dimensional simulations including interactive transport, scaveng-
ing and solar heating of smoke. J. Geophys. Res. 91 (D1):1039-1053.
National Academy of Sciences, Committee on the Atmospheric Effects of Nuclear Explo
sions. 1985. The Effects on the Atmosphere of a Nuclear Exchange. Washington, D.C.:
National Academy Press.
Turco, R. P., O. B. Toon, T. P. Ackerman, J. B. Pollack, and C. Sagan. 1983. Nuclear
winter: Global consequences of multiple nuclear explosions. Science 222:1283-1292.
Representative terms from entire chapter:
solar heating
