re | CHAPTER 2 _ MECHANISM OF ‘TRANSPORT. x The detons ation of a nuciear device releases a tremendous quantity of heat which serves to vaporize the bomb casing and | ' other nearby material and to heat the surrounding air to very adsl Antaneied, high temperatures. The bouyant forces of the heated gas canses the cloud to rise, sucking up quantities of dust and debris. The ascending cloud cools by radiation, entrainment of outside i... air and adiabatic expansion until it reaches equilibrium with its "environment, at which time it is said to be stabilized. In the. dL. continental tests, a short period of hovering at the level of detonation is usually observed, but it is likely that the explo- m . gion itself produced an upward impulse, at least for the MIKE , shot, since the initial rate of rise to about 90,000 feet was reported to approach the speed of sound, Both the MIKE and KING clouds developed the stem and mushroom so characteristic of the atomic explosion, but in the case of MIKE, the dimensions were very much larger than any previous burst. Since the bursts both occurred close to the ground the anomt of debris carried upward was very large. "In previous reports of fallout from the continental tests, a relatively complete discussion of the factors governing the | transport and deposition has been given. Briefly, the movement of the cloud is the result of the horizontal winds, the spread of the cloud the result of vertical and horizontal diffusion aided | by wind shear, and the downward transport the result of scavenging by precipitation, vertical diffusion and gravitational settling. Gravitational settling is undoubtedly an important factor within the first several hours after the burst when the very large particles fall out, but afterwards it is likely that the main descent of the debris outside of rain areas is produced by vertical diffusion rather than gravitational settling. Le A comparison of certain phases of transport and deposition ‘of the IVY clouds with those of domestic tests may be informative . in the light of the different locale and the fact that the IVY clouds -‘penstrated into the stratosphere. Considering first the locale, two essential characteristics differentiate the tropics from the mid-latitudjes. First the trade winds will almost always carry material westward. The upper level - -10-— , Oey