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DESCRIPTION OF AIR AND SURFACE BURSTS 29Fig. 2.07b. The circulation entrains radiations. As the fireball cools andmore air through the bottom of the condensation occurs, the color of thetoroid, thereby cooling the cloud and cloud changes to white, mainly due todissipating the energy contained in the the water droplets as in an ordinaryfireball. As a result, the toroidal motion cloud.slows and may stop completely as the 2.09 Depending on the height ofcloud rises toward its maximum height. burst of the nuclear weapon and the2.08 The color of the radioactive nature of the terrain below, a strongcloud is initially red or reddish brown, updraft with inflowing winds, calleddue to the presence of various colored "afterwinds," is produced in the imcompounds(nitrous acid and oxides of mediate vicinity. These afterwinds cannitrogen) at the surface of the fireball. cause varying amounts of dirt and debrisThese result from chemical interaction to be sucked up from the earth's surfaceof nitrogen, oxygen, and water vapor in into the radioactive cloud (Fig. 2.07b).the air at the existing high temperatures 2.10 In an air burst with a moderateand under the influence of the nuclear (or small) amount of dirt and debrisUPDRAFTCENTERTHROUGHOF TOROID."-,,;:.,. .: \::. ,~,,", ~""',' ~.,CIRCULATIONI h: ,t T GASES( ;t :STEM~_:/~~~ ~~"~::,~ :';~"~ COOL AIR BEING DRAWN.~-! f\:~.." -::: UP INTO HOT CLOUD~ ~/1 c,- .ff~~c 'Figure 2.07a.Cutaway showing artist's conception of toroidal circulation within theradioactive cloud from a nuclear explosion.