makes smoke linger for long periods. Under stable
effective smoke cloud. In order to determine this interval
conditions, smoke streamers tend to travel parallel
you must first understand the basic characteristics of a
downwind for a long distance before they spread and
smoke cloud and the terrain over which smoke will be
merge into a continuous blanket of smoke. Even after
produced. These conditions are described below.
merging, this blanket of smoke lies low to the ground and
reduces visibility at ground level. Stable conditions may
Characteristics of a Smoke Cloud
keep the smoke from rising high enough to cover the top
In combat, smoke-producing devices are used to
of buildings, or other tall objects.
produce smoke screens or smoke clouds of various sizes
Neutral. When there is little change in temperature
and densities. Once produced, the life of a smoke cloud
based on altitude, conditions are neutral. When the sky is
may be described in four successive phases (Figure 7).
more than 70 percent covered with clouds, neutral
Individual streamer. Each smoke device emits a
temperature gradients prevail.
The atmosphere is
steamer of smoke that travels downwind and begins to
moderately stable, and conditions are generally favorable
expand. Depending on weather conditions, the smoke
for smoke. Under a neutral temperature gradient smoke
may rise into the air or stay close to the ground. The
streamers have a steadier direction, and there is less
farther the smoke travels downwind, the more the
tendency for them to rise than when they are under
unstable conditions. Also, streamers tend to spread and
About 20 to 30 meters downwind,
rise more quickly than under stable conditions.
individual smoke streamers begin to merge. This merger
Therefore, neutral temperature gradients are best for all
point starts the buildup phase. The screen becomes
thicker as several smoke streamers merge. However, the
Lapse. The lapse (unstable) temperature gradient is
screen is not uniform at this point because parts of the
just the opposite of inversion. The air temperature
screen have more smoke particles than others.
decreases with an increase in altitude.
Uniform. After the smoke travels about 50 meters,
conditions make smoke break up because the air is
the screen density becomes uniform. The same number of
moving. In low winds, during unstable conditions, the
smoke particles exists in any part of the screen. The
smoke streamer may rise abruptly from the source. In
uniform phase of the screen usually travels downwind
higher winds, the streamer may pass only a short distance
about 2 to 6 kilometers. Local weather and terrain dictate
downwind before rising and becoming diffused.
the exact length of the screen.
Practically all smoke absorbs moisture from the air.
Terminal. Eventually, the smoke screen breaks up.
The smoke particles absorb moisture and increase in size,
Large smoke particles settle on the ground, and smaller
thereby increasing their density and making the smoke
ones dissipate into the air. In this phase, the screen
more effective. Most smoke munitions produce a denser
becomes so thin that it no longer degrades vision of
smoke when the humidity is high than when it is low.
Therefore, high humidity is always favorable for smoke
Light rains decrease visibility; therefore, less smoke
Visual observations are used to determine the type of
is needed for concealment. Heavy rains and snow reduce
terrain over which a smoke screen is to be used. When
visibility to the extent that smoke is rarely necessary to
using the spacing guide (Figure 8), only two types of
terrain-water/open and wooded-are considered. After you
have determined the type of terrain, the wind speed, and
temperature gradient, you can determine the spacing (in
Since smoke is carried by the wind, it normally
meters) of smoke pots by looking at the spacing guide.
follows the contours of the earth. On flat or unbroken
Example: Determine the spacing for ABC-M5
terrain and over water, smoke streamers take longer to
smoke pots to produce a smoke blanket under a neutral
spread out and mix together. On the other hand, trees and
condition in a wooded area with 13 kilometers per hour
buildings tend to mix smoke streamers and increase
smoke coverage. Large hill masses and rugged terrain
First, look on the spacing guide for the Wind Speed
cause strong cross currents that disperse smoke, causing
column to locate 13 kilometers per hour. Read across the
holes and unevenness.
1 to 14 kilometers per hour line to the Temperature
Gradient column for the neutral condition. Continue
across the Terrain Description column on the wooded
Part D-Determine Smoke Pot
line. Continue across the Position Spacing column for
The spacing of smoke pots is the measured distance
Haze and Blanket figures. You will find that the distance
interval between positions necessary to produce an
between smoke pot positions for a haze is 70