3e The constancy of the measured heisht of the top of the éloud over a period of one heur in Table I is consistent with the slow movement of the cloud. easurements by Colonel Fee in the aircraft to the east of Ground zero ere not so consistent and calculated heights eppear to decrease rith time, probebly due to an increase in true base line coving to a nestward movement of the cloude Colonel Fee's date place the tcp cf the cloud variously betyveen 127,009 and $9,000 4. feet. The rate of rise of the cloud can be chtained frecm Figure I. It 4s to be noted that ea marked vertical ceceleration cccurred at two rinutes, at which time the conspicuous lateral spreading occurred. This is in agreement with the cbservations of C. E, Falser except that actual Reasurement indicates the “splashing” cecurred against a berrier betvcen 100,000 and 110,000 feet, vhich may be of significance in connection vith the usual increase in teciperature at arcund 100,000 feet. Some chservations given to Dre Urry by Col. lcrris in the 5/36 sampling control aircraft cre plotted also in Figure I. Col. Licrris*s cbservation at 40 seconds as the cloud went by his altitude is in fair agreement with Dr. Urry's curve as also is his observation some tine after 20 minutes. At five minutes, Col. Merris*s observatien is considerably lower than Dr. Urry's but the top is wall within the stratosphere. Se Sone observations by lr. Singlevich of Headquerters USAF, AFCAT-1 under similar conditions, but at 30 to 4C nautical miles frem ground zeno at the time of IVY King test are shown on Figure I fcr ccrperisone be The hypethesis put forware by Professcr C. E. Palrer in his second letter of 2 Fetrucry 1953 fer the seccndary fermetion of the main large cloud appears to the author to be plausible but it elso appears equally certain thet the bulk of this main cloud ended up in the stratosphere between * 60 and 120 thousand feet. The maintenance of its shape and form are believed to be due to its internal turbulence and unequal heat distribution. Any estimate of the decree of mixing of the secondarily fermed large main cloud vith a primary column of nuclear debris, if indeed this did not intinately occur during rise, is purely hazerdous guessycrk. As far as is known, no observations were made for guidance on this aspect of the problem. It seems apparent that sampling was conducted some thousands of feet below the bottom of the main cloud, as statements by scme of the pilots cf the F-&4 sampling aircraft, appears to confirm. Te There is attached hereto es an integral pert of this prebdlen a memorandum from bre Pe He Allen tc Dre %. D. Urry dated 11 December 1952, © discussing a well-defined relation between early rate of rise cf the cloud and the energy of a nuclear explesicn. te De URRY Assistant fcr Nuclear Pnysics Lf aA Office of the Technical Director, AFCAT<-1 3 Inels Table 1 Figure I Meno dtd 11 Dec 52 fm btr. Allen to Dr. Urry Copled/DOE 7 “- 2 ee ee a its, LANL, J-Div. |” = ~ = . -