Description of the The ZEBRA Day cloud in its initial stages mas about nine miles avey, Per- ZEBRA Day Cloud This projected portion of the cloud rose mtil about the twelfth minute haps because of its nearness and the uncbstructed view, the flames in the fireball when it began to spread out. At about the tenth or eleventh mimite, the top of the seemed brighter and appeared to last longer than those of previcus weapona. cloud had moved to the east of the broad stem, and observers om the U.S.S. Bairoke the first tro mimites, the clowl! wae rising almost etreight up. During The cloud had the were able to look up into the base of what had been the rising mshroom head, The familiar mshroow form, but the head of the cloud did not have a well-defined circu- observers on the Bairoko stated that the cloud, viewed from the bottom, had « bollow lation after the secomd minute, appearance and looked somenhat like a smoke-ring. There was more cloud mterial in At the end of the third minute, the upper part of the cloud began to move torard the east, as it became subjected to the westerly winds. the edges of the cloud than in its center. From the third minute until after the eighth minute, there was little change in the part of the cloud appeared to break away, but it never did get far from the min body sbape af the atomic cloud, of the cloud, the east. It contimed to rise and was bent more and more tora By the ninth minute, the finger-like projection which rose out of what had been the primary portion could be seen plainly. It appeared timt a relatively smaller At the fifteenth nimite, the finger-like It was noticed, about this time, that the lower extremity of the atomic cloud ended at the region of shear betreen the easterly and westerly winds, near an elevation of 7,000 feet, As for as could be seen, there appeared to be no cloud bubble of hotter gases was contained within the primary portion of the atomie cloud, paterial which could be definitely observed as the atomic cloud below that level. and that this relatively hot bubble did not cool as rapidly ae the remainder of the Fron the fifteenth minute up to one hour past H-hour, the cloud consisted of three cloud, primary parts, When the primary cloud mass stopped rising, this bubble continued its rise for an additional 5,000 feet before cooling to the temperature of the surrounding air. They were a cloud streamer, the remains of the uppermost finger-like projection; a large globular mass, the primary portion; and the long tenuous stem. After one hour, the edges of the atomic cloud began to be indistinct, and the cloud began to blend with the thin cirrus clouds which almost completely covered the aky. Then, et one and cue-balf hours, the outline ef the cloud became imlefinite. Finally, at H-bowr plus two hours, only a light tan patch remiined of the primary cloud mass; and no other parts of the atamic cloud could be seen. This cloud seemed to be entirely composed of smoke and dust with no suggestion of moisture, No 4ce cloud or cirrus veil on the top of ths mushroom was reported,