User Guide

ATMOSPHERIC EFFECTS OF BLASTS
The Mushroom Cloud. The heat from fusion and fission
instantaneously raises the surrounding air to 10 million degrees C.
This superheated air plasma gives off so much light that it looks
brighter than the sun, and is visible hundreds of kilometers (km)
away. The resultant fireball quickly expands. It is made up of hot air,
and hence rises at a rate of a few hundred meters per second. After a
minute or so, the fireball has risen to a few kilometers, and has
cooled off to the extent that it no longer radiates.
The surrounding cooler air exerts some drag on this rising air,
which slows down the outer edges of the cloud. The unimpeded inner
portion rises a bit quicker than the outer edges. A vacuum effect
occurs when the outer portion occupies the vacuum left by the high-
er inner portion. The result is a smoke ring.
The inner material gradually expands out into a mushroom
cloud, due to convection. If the explosion is on the ground, dirt and
radioactive debris get sucked up the stem, which sits below the fire-
ball.
Collisions and
ionization of the cloud
particles result in
lightning bolts flicker-
ing to the ground.
Initially, the cloud
is orange-red due to a
chemical reaction
when the air is heated.
When the cloud cools
to air temperature, the
water vapor starts to
condense. The cloud
turns from red to
white.
In the final
stages, the cloud can
get about 100km
across and 40km
high, for a megaton
class explosion.
VDSG – RESTRICTED – VTB-OO1-13
RESTRICTED 1—3
If you see the flash, duck and cover!
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