explosive conventional weapons, not only in explosive effects, but in the
widespread effects of radioactive fallout. Most of the fallout will settle
back to earth within the area of ground zero. However, large quantities of
fallout particles will be carried downwind of ground zero by the upper air
Due to the lethal effects of fallout on personnel, commanders
must have the personnel, equipment, and knowledge necessary to determine the
Through this determination, the commanders can take the
necessary actions to protect troops and equipment.
A current Effective
Downwind Message in the hands of trained personnel can provide the commander
with the information necessary for a life-saving decision. To develop the
information, it is necessary to know how to make a wind vector plot, compute
nuclear data, prepare an Effective Downwind Message, and the procedures for
disseminating the Effective Downwind Message.
When a nuclear weapon is detonated, it is characterized by the mushroom
cloud reaching high into the air, the brilliant flash, and the tremendous
blast. The mushroom cloud created by a surface or low air burst is debris
being picked up, vaporized, and becoming radioactive. The majority of this
material will fall back to earth in the vicinity of ground zero; however, a
large amount of these radioactive particles will remain aloft and will be
carried away from ground zero by the wind. The final location of fallout
depends mainly on the heights from which the fallout particles start their
descent and the wind structure between the ground and various parts of the
nuclear cloud when these particles are falling. The heights from which the
particles start falling depend on the yield of the weapon, the size of the
particle, and existing weather conditions.
Thus, since the yield is
determined from nuclear burst information, the reliability of the fallout
prediction depends to a great extent on the upper air wind data and the
nuclear burst information available.
The wind vector plot is used to determine the lateral limits of fallout, the
effective downwind direction, and the effective wind speed.
This plot is
prepared by the NBC Center (NBCC) on receipt of new upper air wind data. It
is prepared on overlay paper, oriented to grid north, and drawn to
The plot consists of a series of vectors representing
wind layers between the surface of the earth and the height to which upper
air wind data are obtained. The vectors are plotted head to tail, and each
vector represents the distance and direction a nominal size particle would
travel over the earth while falling through the wind layer.
size particle is defined to be of such size (a spherical particle 143
microns in diameter) as to require 3 hours to fall from a height of 11,000
meters to the ground.
The significance of the wind vector plot is that
after it is oriented by the GZ tickmark and grid north, it represents a
series of points on the ground where the nominal size particles