rn LAT) nee Description of the XRAY Day Cloud Between the twelfth and thirteenth minute, the mushroom reached its highest The atomic cloud pushed through the deck of broken cumulus clouds almost inmediately and was above the highest cuwsulus shortly after the first minute. During elevation, The highest elemation angle was recorded at this time, Almost immediately, the period of most rapid rise, the cloud showed the internal oirculatian which ms a thin cirrus plume formed when a protuberance from the top-most part of the cloud ex- observed at Bikini and was in the charecteristio mushroom shape, As on ABLE Day at tended up into the northsasterly wind which ms in the stratosphere, To « ship-borne Bikini, several short clowd streamers, or spurs, seemed to project outward at an angle observer, this cirrus-like plume first appeared to extend upward and westward from neer from the bottom of the cloud at the time it was rising most rapidly. the center of the globular mse of cloud which had shortly before been the rising msh- Also, as at Bikini, when the top of the cloud reached 40,000 feet at apprarimtely H-hour plus roum, The base of the plune became brosder while the tip remuined pointed so that the 5 minutes, an ice cap was sean to form, The darkness prevented careful observations, goneral effect was that of a bird's wing extending horisontally from the cloud in the end all of the observers did not report this ice oap phenomena. Urection of the ships. i The upper portion of the atomic cloud was estimated to be approximtely 5,5 At the sixth mimite, the cloud top was approximtely 44,000 fect and the sketches show that the cloud consisted of two mjor portions, the mahroom with its miles in diameter at the time it reached maximum altitudes, and ite center was 19 wiles tapering stalk and a Jarge cumjlus-type cloud from which the stalk appeared to extend. distant from the observing ships, This lower cloud portion reached up to an estimated height of 15,000 feet and wa mingled with the other lover clouds so that it was mostly obscured. As the mushroon mass moved with a wind from 230 degrees at approximately 25 knots, as the wind-shaped sheet of cirrus above trailed behind. contimuad to rise, it began to move eastward with the prevailing southwesterly winds. This drift to the eastward began between the third and fourth simute when the cloud reachad approximtely 30,000 feet. Meanwhile, the lower portion wa drifting west- ward, and the stalk or stem wes elongating and becoming smaller in diameter. At nine minutes and thirty seconds past H-hour the U.3.5. Albemarle ob- After reaching muximue elevation, the upper cloud Toe TRAY Day cloud disappeared from view in the following mumer, Tha lower oumlus-type portion of the cloud remained visible until about H-hour plus teenty sinutes and then was lost to observers because of other clouds, The stalk of the muskrooa formed a broad, irregular shaped area of fina dust and smcke which appeared to disperse jtaelf in the region of wind shear. This amoky patch disappesred at about H-hour plus servers recorded a olenn break between the upper and lower oloud masses and this shear two hours, Meanwhile the primary portion maintained its general shape but appeared to wes estimated to ooour at 20,000 feet. The stem of the cloud rapidly dispersed in become thin and shast-like so that it closely resembled olrroowmius, Finally, et this region of wind shear during the following three or four minutes, leaving an approciestely H-hour plus three hours even this most prominent part of the atonia cloud irregular patch of dust or smoke which separated itself fram both the upper and lover sould not be distinguished by surface observers. portions of the cloud.