Because the cloud did not cool at the same rate uniformally throughout its volume, a vertical distribution of cloud material was observed at stabilization. In the simple case of an ideal, strongly streamline toroidal circulation of the outer portions of the cloud cooled more rapidly and stabilized at lower altitudes than the inner portions, Considerations of the surface relative to the volume of a cloud indicated that the altitudes of the top and base should be observed to be a power function of the yield of the explosion in a uniform atmosphere, Scientists frequently observed the temperature profile of the atmosphere above the tropopause, however, to be isothermal or sometimes to show a positive lapse rate, such as inversion, Clouds from higher yield explosions, therefore, had their rise strongly dampened by this temperature structure when they rapidly attained temperature equilibriumwith the atmosphere above tropopause altitudes, The altitude of the primary mass of cloud material was related to yield. Scientific personnel made observations at the Nevada Proving Grounds of many explosions both at moderately high altitudes and relatively close to the ground, the range of burst height in most cases lying between ,000-5,000 feet mean sea level. No attempt was made to correct for difference in height of burst for these data since particular atmospheric conditions such as temperature inversions, degree of wind shear, and humidity appeared to affect stabilization altitudes more than moderate differences in turst height. Because of these factors as well as the effect of the stratospheric 20h APOL/un SWEH -2-0034 ye? 4 . @t: