Cloud Height and Sampling Altitude Although a number of hydrodynamic and other phenomena accompanied a nuclear explosion, a few of the pertinent physical characteristics involved in the rise and stabilization of a cloud directly affected sampling techniques. The hot tubble of gaseous and particulate.debris, remaining after explosion, had a temperature of several thousand degrees centigrade, This bubble displayed a large vertical acceleration because its density was mech lower than that of the surrounding air, During the initial stages of: its rise, a toroidal circulation (smoke-ring) usually formed in the bubble which for sufficiently high burst heights is markedly_ streamlined, For bursts near the ground this circulation appeared to be disturbed by turbulence to a degree which was dependent upon initial burst conditions, As the stabilization altitude approached in the later stages of rise, this toroidal circulation weakened and eventually ceased to exist. By adiabatic cooling as the cloud rose through lower and lower atmospheric pressures | and by the far more important process of entrainment of cooler air fron the external atmosphere, the temperature of the ascending gas bubble fell rapidly. The temperature continued to fall until at some altitude the | cloud attained density equilibrium with the external atmosphere. Momentum carried portions of it past the initial equilibrium altitude, but as adiabatic cooling contimed the density of these portions became greater than that of the ambient atmosphere and their rise stopped, Subsidence occurred then to an altitude somewhat above the initial equilibrium point, 203 AFWLJHO SWEH-2-0034, A peo c