wd ' accurate observations of the character of the cloud. The winds were easterly to 5,000 feet, light southerly above to about 30,000 feet, becoming westerly about 30-0 knots to the tropopause. Secause of large amounts of. fakteut from the second burst, which occurred eleven days earlier, it was impossible to trace the history of the debris from Koon. According to the meteorological trajectories (Figure 2.4), ‘the ‘lowest layers moved westward, the mid-tropospheric portion milled about to the north of the Marshalls for many days and the upper portion moved eastward, remaining south of the Hawaiian Islands, reaching the southwestern states on April 13. No fallout station reported debris which can be definitely assigned to this burst, although it is likely that some of the activity assigned to Romeo is a mixture of debris from the two bursts. No fallout has been assigned to Koon in this report. -, 2. UNION vy \ The fourth test of the series, Uniondetonated at Bikini at 1810 GCT, April 25, 19She¢ The wind pattern was ‘typical, easterly tradesin the lower levels, light winds above, becoming westerly near the tropopause, and strong easterlies above 70,000 feet. Trajectories of this burst are shown in Figure 2.5. If the 30,000- and 40,000-foot trajectories are correct, very little fallout was evident from these levels, since no debris was detected in Mexico or along the Gulf cosst util May 5 or later. Fallout at Medford, Ore., on May 2 and in the western states on the. following days is in good. agreement with the 18,000-foot meteorological trajectory. It is very possible that the lack of mateorological data resulted in erroneous trajectories at 30,000 and 10,000 feet, since debris arriving in Central and South America on May 5 was most likely transported at these levels. Fallout to the west of Bikini seemed to be in good agreement with the trajectories. It should be noted that even though a month had elacsed since the last burst, considerable fallout is occurring throughout the tropics mid It is by no means certain that the debris assigned to Union is not from an earlier burst, or that some of the activity Bssumed to be from Romeo is not actually from Union. b Wi 2.5 YANKEE Yankee, the fifth burst of th8-s8Mies, was_detonated from Bikini at 1810 GCT, May hk, 195h. 1 -12-