World-Wide Fallout from Operation Castle

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-. coNTlarrs

ACKNM~EMENTS ...... - .

ILLIGIRATIONS......

ABSTRACT...... ,o ...... CHAPTER1 INTRODIX=TION...... cH@!TER2 CASTLETESTS ......

2.1 Bravo . . a...... 2.2 Romeo ...... 2.3 KOOIL ...... 2.& Union ...... 2.5 Yankee...... 2.6 Nectar...... * ...... cHApTEp.3 WB,LD-WIDEFALLOUT...... 3.1 Castle Total...... ohils for IndividualTests ...... ::: F oqarispn.'&ith Total Beta Yield...... 3.11 l?ZEGGZogical Interpretation......

3.5 ~imum Activityat . IndividualStations l .,.-.z_,~__,_ PC. ._. mm& SPECIALClBSElRVATIONS .... , ...... 38 APPENDIXA MAPS OF DAILY FALLOUT,...... 39

...... l 220...... __ ...... ”

ACKNWLEDGEMENTS

The work reportedon here was performedunder the directionof Dr. Lester Machta,C.hief, Special Projects Section, Scientific ServicesDivision, U. S. xeatherBureau. The monitoringprogram was establishd by the Healthand Safety Laboratory, New York Operations Office, Atotic EnergyCommission, Merril Eisenbud, Director, arx?that office provided tIx radiological-data. Mr. Daniel E. Lynch of the Health and Safety Laboratoryserved as coordinatorof the program.

Msv helpfulsuggestions were rece!i.&dfrom colleaguesin the SpecialProjects Section, D. Lee Harri.6,Kenneth M. Nagler,Francis Pooler,Jr., and Leo B. Quenneville. The staffof .tbissection performedthe laboriousand pemstax3ng plottingof data and prepara- tion of the finishedmanuscript. - iv.- ..

ILLIETRATIONS

Page

* 1.1. Fallout Monitoring Network, Pacific Hemisphere ...... 2 1.2 Fallout Monitoring Netuork, Atlantic Hemisphere...... 3 2.1 Winds Aloft for Castle Events...... 7 2.2' Meteorological Trajectories for Burst No. 1, Bravo . . . . 8 2.3 FESteoroIogicalTrajectories for Burst No. 2, Romeo . . . . lo; 2.L Meteorological Trajectories for Burst No. 3, Koon. . . . . 13 2.5 Meteorological Trajectories for Burst No. 4, Union . . . . lb 2.6 Meteorological Trajectories for Burst No. 5, Yankee. . . . 16 2.7 i%teoz?ologicalTrajectories for Burst No. 6, Nectar. . . . 17 3.1 Total Fallout From Castle Series as of July 1, 19511, PacificHemisphere ...... 20 3.2 Total Fallout From Castle Series as of July 1, Gl, Atlantic Hemisphere...... 21 Total Fallout From Bravo, Pacific Hemisnhere ...... 2J.4 Total Fallout From Bravo, Atlantic Hemisphere...... 25

Tot,& Fallout From RomeiS.Pacific Hemisphere . . . . . l . 26 3.6 Total Fallout From Romep,.AtlgnMc Hemispher_et 3.7 Total Fallout From Union, Pacific Hemisphere ...... 28 3.8 Total Fallout From Union, Atlantic Hemisphere...... 29 3.9 Total Fallout From Yankee, Pacific Hemisphere. , . . . . . 30 3.10 Total Fallout From Yankee, Atlantic Hemisphere ...... 31 3.11 Total FaJ_out From Nectar...... '-.. * . . 32 3.12 &ximm Activity on Sampling Day at Individual Stations, Pacific He.misphere. . . . . ,...... 34 3.13 ~aximm Activity on Sampling Day at Individual Stations, l Atlantic Hemisphere. . . . . i ...... - ...... 37 A.1 + A.186 Radioactive FaQout i& the 24-hour Periods Begin- ning February 28 - May 31,:'11954...... _. .40-225

& j A.l@ - A.188 Average Daily Fallout During Month of June, 19~..__._...,...... -- - wb-227 s- . ABSTRACT

A world-wide netvworkof gumned film stations xas established to monitor fallout followiq Operation Castle. Xlthoqh meteorological data were poor, a general connection of troyos?heric flow patterns with observed fallout was evident. There ws a tendency for debris to re.win in tro?ical latitudes, with incursions into tk teverate regions associated with mtecrological disturbances of t.he predo.tinantlyzonal flou. As tha season advanced, such incursions becam more evident. Outside of the tropics, tLhesouthwestern United States received the greatest-_ total fallout, about five t_imest-hat -received in Japan.

._^_...... _~. .._ T.he.mximuin fallout-on any day at an individual station in the &G.t.edStates, corrected to [email protected] day, was 200,000 d/m/ft2.

It is concluded that the probability of early fallout in inhabited regiok would be reduced bp holding Pacific test series in the wkter months.

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‘.Lindicaticns that the arbitrapJsystem ';lgs in error,the activitywas (’ In L reassignedto the appropriateburst. the case of observationsin the Pacificand adjoiningregions, it was usually possible to determine the burst respocsible for the activityfrom an exarcdnation ; .I of the trajectoriesof the debris in conjunctionwith observed c- increasesin radioactivity.Elsewhere in the world,it was ordinarily necessaryto use the arbitrarilyassigned burst. 4.1 maps of daily falloutvalues indicate the burst assignmentused in computingthe decay correction, Unlessotherwise indicated, all radioactivityis reportedin units of disintegrationsper rrdnuteper squarefoot of greed film, decayed_-- to 100 days after the dev ---of the burst. The twTo2 law for the decay of fission prodscmty has been used throughout.

The maps of.daily falloutinclude only the data from the land stations,since there is considerableuncertainty in the ship data. The locationsof the shipswere Imperfectlyknown and the procedures for avoidingcross-contatination of samolesin handlingand mailing, particularly on ships exposed to heavy fallout at soT?etime d$.ng . their voyage, were not adequate. The SND data were utilized in the drawire of isol,ines of activity on the failout m~s and in the intepretatior! of theI land staticn data.

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The bursta of the Castle series are given in Table 2.1. . Table 2.1. Castle Test Series

'Burst Yield & Ho GCT Total -0 Bravo Feb.28 18U 15 Rome9 Mar.26 1830 Koon Apr. 6 1820 L&on Apr. 25 1810 Yankee P'bY 4 1810 Nectar by 13 lE20 ,

The first burst was detonatedon .B-&bi Atoll,-%fi succW%ng~~four from barges in the Bikini lagoon and the las; on Enik-etokAtoll. 4. . most of the radioactiveclouis created in tk Castle seriesextended to very great heights, and the greaterpart of the cloud in levelsbeyond tk reach of routine meteorological observations. For this reason, it tis been Possible to prepare adequatemteorological ';rajectoriesto dete&e tte cath of the debrisat variouslevels. T&network of uper air obserm stationsin the tropicsis etireir.elysparse at best, and wind reports at levelsabove &O,OOG feet-are'virtually nonexistent, with the exceptionof a few-fromstations in the l&shall Islandsand adjacentareas established-especially for this test series; hen at these stations,the highestotiservations rarely extend above I 100,000it. 4 ..x :

c The meteorologic81 trajectories for the variousbursts C8nnot, therefore,be computedet levelsabove &J,CQO ft. and are doubtful even e&lower lemls, 811 trajectoriesgiven in this report were computedby personnel of the Air WeatherService- @uPA Branch)and ri-eprepared for the 8SO-mb.r(s,OCCLft), 70041. (lO,GOO-ft.), SOCI-mb.(18,0O&ft.), 3004nb. ~3O,CKX+.~, and 2OO-nb ~40,00M3.1, lemls only. b The tenperaturesottndings for all of the Castlebursts were very similarin their major feetures. There were no pronounced invwrsionsin the lowerlayers (exceptfor an inversionat about 7,000feet duringRomeo). The air w8s quite moist up to ebout 5,ooOfeet, end somewhetdrier shove,with fairly SteeD 18pSeretes in the upper troposphere.The tropopausew8s between&8,ooO erxi 9t,oo0feet with very stablel8DSe r8fXS in the lOwi3rStr8tOsphere ebove, The winds obtainedfrom observationsmade at or near esch of the shotsare shownin Figure 2.1. . ?’F ,‘” - _L : .- 2.1 BRAVO , _L(.

The first burst of the Castle series,Bravo, MS detonatedfrom 8 coralreef in BikiniAtoll on 181r5GCT, February28,_1991. The resultingcloud of radioactivedebris reachedto feet Tha tropopause at this time ~8s at about s&,ooO feet, The low-leveleasterly tredes extendedto about 6,000 feet, with light westerlywinds incre8sing with 8ltit7Xie to 8 maXimUm Of aboqt ho knOtS at 35-b0,000 feet, Satiily xinds extendingto the kiss2 cf 2-z strah,~hzre. preFaiied . throughoutthe stratosphereto the highesteltitude reached by the meteorologic81observations, about 100,000feet. Winds 8tthislevel were eesterlyat about 50 knots.

Trajectoriesof the lower parts bf tf-ecloud are shown in Figure2.2, but unfortunately,no trajectoriescan be constructed Tozbtb high3rlevels. Availableevidence to about lCG,OGCfeet o servationsin the .hrstillsand at Guam) indicatesgeneral essterly winds in the lower stratosphere,so that this portionof the cloud moved toward the Phillipines.ho observationsto indicate the mov8- ment of the cloud above lOO,OoO feet 8re availeble. However, it is likely thet essterly winds prewiled et these levels.

The daily f8=0& maps for the period following th&Bram> test 8re particulerly interesting in that t%e background of fission product activity from previous tests Was negligible and the succeeding burst d%d not occur until 26 d8yS leter, so that the progressionof areas of falloutfrom dsy to day is more easily seen. 5 KNOTS too - + +

+ +-?a. 4 + 90

w 80

W cl g 3 30 a

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+ i/- P P 0 ...... 2 BRAVO. K&i UNION YANKEE NECTAR ENIWETOK lO”7’N 16S06’E ENIWETOK ENIWETOK ENIWETOK 4 WIIP) 1000 GCT 2100 GCT 2100 GCT IS00 GCT I500 ect 20 FEB. -6 -*m, 25 APR. 4 NAY 13 NAY

FIGURE 2.1 WINDS ALOFT FOR CASTLE EVENTS

7 ~_~~~_~~~~~ _ __ .___ ------__-J- . \ i : s3 - .--_ _.___-__o’- %.. 2 w I _-_--- - . ‘N ti w

8 The eiastuard mow debris reached the Americason March 9 and 8, indicatingan average westi wind of -about40 knots, in good agreeaaantwith the few tid,observationsavailable in the upper troposphere.Although the progressionof debris to the west appearsto be in good agreeraentwith tha 5,0&I-foottrajectory, indicatingthat the transportoccurred in the trade wind layers, it is entirelypossLblethat stratospheric debrismoving with the tpperlevel easterliescontributed to this falloutalso.

The most stiking fact which emergesfrom a study of the falloutin the period followingthe Bravo test is the tendency far the debris to remain in the tropicallatitudes. By far the largestamounts of falloutoccurred in the latitudeband from 10'S to 20*N,+ith occasionalexcursions into the more temperate latitudesof each hemisphere,particularly in the Americas. An exampleof this can be seen in tk southwesternUnited States in the period beginningMarch 1s. At this time, a deco low pressure systemextending through most of the tropospherewas locatedjust off the vest coast, with strong s0ut.hesterlpwkds over thz southwesteRls+yates. This depressionmoved slowlyeastward so t.hat by March lath,,the sonth~estarlywinds mre over the Xississi>pi ~8~8y. An examinationof the falloutmaps reveals tihatfallout during this period was associatedwith t.kesoutkesterly winds, which carrieddebris from the tropicalregions. It is signM.cant that this falloutMS independentof precipitation.The Ihighest falloutValues occurredduring the first Uhree days of the period when there was no precipitation,and even on the 15th, when there uere severalstations reporting precipitation, the fallout occurred ,in the region dominatedby the southwesterlywinds and uas not, closelyassociated with the existenceof precicitation;'A somewhat simihr seriesof events occwreci_int&he period Xarch 21-25,although precipitationwas more uidespreacL% this case and may have had more influenceon the observedfallout patterns. . i

The secondburst of the Castle series??.o~eo? WJS detonated frm-'a'%argeat3833GCT-Xarch 26, 195!!

The Kind observationsassociated with this burst- showed light easterlywinds at virtuallyall levels increasingin 4 speed above SO,w feet to a m&&&n of 92 knots from the SE at the top of the highestobservation, 9!&000 feet. nthoughx'he tra.jec'%orle.. @igure,2.3)at all levels in$he:3ropospnaremoved westward $.nit,ially,the 30,000-and hO,OOO-foottrajectories curved northward

-9. _.-_ -..--_.: .___

-.-.- -._..-__ and then eastward within a very short time. The lowest levels con- tinued westward and the 18,000-foot trajectory appeared to curve back towards the United States on the 28th, although the meteorological data is uncertain. Winds in the stratosphere up to the t level of the tOD of tha cloud were probably from the east, carrying most of the mushroom westward.

A1thoug.h almost a month elapsed between the first and second bursts of the. Castle series, enough’debris from tha first burst was present to seriously interfere with attempts to trace the progress of the second cloud by an examination of fallout data. For example, an increase in deposited activity occurred at some stations in Central and South America on March 31 and -4pril 1, several days before the meteorological trajectories would indicate the arrival of debris, It is not certain if this is due to the complete lack of meteorological observations in the Eastern Pacific and the winds were really stronger than assumed, or that the debris was actually from t.he Bravo burst. (Note: Since all fallout data is extrapolated m to 100 days after the assigned burst, values ssfiq?t?d to different bursts cannot be comzared d5rectly. The extraoola tion factor denends both on the day,of t.he burst and on the day the saqle *wascounted. For the areas mentioned in this oaragrarh, values assigned to burst 2 would have ‘XI be increased by about a factor of three if the debris

here ? ssiqed._..ta_ .. -burst- 1) . By April 2nd and 3rd ,increases in a cti :

4 Koon, the third burst of the qies was de tontiY&da t Bikini 3%13‘20 GCT, Aoril 6. 19%. bit. cloudy conditions prevented

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accur8te observations of the Character of the Cloud. 1L ---I .._I_ _. The winds were easterly to 5,000 feet, light southerly above to about 30,000 feet, becoming westerly about 30-40 knots to the tropopause. tiecauseof large amountscf f&Lout from the second burst, which occurred eleven days earlier, $t was impossgble to trace the history of the debris from Koon. According to the mtecr~logicaltrajectories (Figure.2A);the ,lowest layers moved uestvard, the mid-tropospheric portion milled about to the north of the Marshalls for many days 811dthe 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, elthough it is likely that some of the activity assigned to Romeo is a ndxture of debris from the two bursts. No fallout has been assigned to Koon in this report.

2.4 UNION 3 : ,i? The fourth test of the series. Union'iK.deton8tedat 3ikini at 1810GCT, April 25, 1954~ T.hewind pattern was 'typiC81,easterly trade33 the loam+ levels, light winds above, becoming westerly near the tropopause, and strong easterlies above 70,000 feet. Trajectories of this burst are shxounin Figure 2.5. If the 30,000- and 40,000-foot trajector,,ias are correct, very little f8llOUt 118sevident from these levels, since no debris MS detected in %?xico or along the Gulf co8st until &y 5 ,or_later._Fallout at &dfotid, Ore.,.on Pay 2 and in the!western states on the.following days is in good agreement with t& U&000-foot meteorological trajectory. It is very possible t-hat'thelack-of mateorological data resulted in erroneous trajectories at 30,000 and 40,000 feet, since debris arriving in Central and South America on May 5 MS most likely transported at these levels. Fallout to,t.he west of Bikini seemed to be in good agr,,.'oavnt kiltht:be irajectcries. It should be noted that even though a month had elapsed since the last burs3 considerable fallout is occurring t.!roughoutthe tropic_a,qZ5i% is b;rno means certain that the debris assigned to &&n is not from an earlier burst, or that some of the activity Bssumed to be from Romeo is not actually from Union.

-.-- 13 2.5 YAtiE _.,_ l . _.L_§ Yankee, the fifth burst of th2jXER5es, w8sAe_$ona_tedfrom Bikini 8t 1810 GCT, May 4, 1951r. ,

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-... . ._-.-- Although the winds, In general, were similar to those of the previous bursts, th3 westerly winds just belo-wthe -tropopauseattained Mgher speeds t than had occurred during the previous tests, 55 to 65 knots at to,000feet. '&ajectorie.sare shown in Figure 2.6. ‘-D&F33 z-wads?‘- +%tq on f!bj a, iaci fal.l%$t-+~ i-id&$reedeve, I;tbe-wq&ern@ins&ates and the Rockies by %yg. ~8~oul;~from this burst cmtinuad over t& w&tern &If of tti Mted States . (wj.ththe exception of the P8cifi.cCoast) in significant amounts for 8 period of more than 8 week. The falloutfrom Yankee in this xegian exceeded, by almost an order of magnittlde,the fallout from =~,_~~,the other tests of the series. The westward moving debris appeared to proceed faster than indicated by the low-level trades, reaching Koror by.May 6 and Singapore by my 9. Again, it is Very possible that high-level easterlies carried the debris, aince the. '2$3O knot uirds required are somewhat fester than expected in the trades of t& Western Pacific.

2.6 NECTAR

The last test of the series, Nectar, was tiaa only burst detonated from Fsriwetok. It occurred at 18x) GCT, ?by 13, 19%,

“an,.1 +4 -_. .,Y _.._) _-_T_‘_r ; -- -‘,- ‘fz +t,- --i& ?!-i! - _ & -i_. _.’ \. easterly Kinds e;;stir.,ti~CG .LJ,&~ ;eet, with &gut wasterUes abov.. to the b8se of the stratosphere. The trajectories from this burst (Figure2.7) began with 8 slightly greater component towards the north than for the previous bursta. l Slice Yankee and tictar &re separated *by only Nne days, it is virtually impossible to distlngui~h between debris from the two bursts. An attempt to separate the two sources of debris was made for tha first mek follo>@r~ Nactar,. but. MS not attempted bayond this time. Da-fly fallout maps for the remainder of the month, &y 22-31, are given with all dab extrapolated to 100 deps after &actiar because of the arbitrary system of burst ass;_gnment used. However, it is likely ttit the major portion of the fallout reported on these days origin8ted from Yankee. To convert the reported activity to 100 days after Yankee,assumi~ the debris originating from Yankee, the ~811~s given on the maps should be increased bs &nllL304&

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H ba To conserve space, daily.fa.Ilautlnaps for the month of June hre.notsbm. Rather,a map shovkngthe averagedaily fallout for the month is given, together-with the number of days for which data was available-atesch station. Again, the extrapola- t#ar fsbased o~%.Nectar,and activityia shown at 100 days after burst. It 18 also likely that the Ilvljorportion of the fallout ul.Jme originatedfrom Yankeeand all 'vales shouldbe increased by rbout 258 to give -valuesat 100 days after Yankee. b

Althoughths discussionof the transportof debrisin the atmospherehas been confinedto essentiallyhorizontal tmjectcries, the actualpaths of individualradioactive particles are complex, three-dimensionalphenomena, influenced by the fall velocitiesof. the particles,atmspheric turbulence,rain scavengingand orographiceffects.

J _’ .P 1 ! . _,._ ._..... -3

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c TOTALWCRLD-WIDE FALLOUT

3.1 CASTIE TOTAL . Tha total world-wide fallout from ea.chof the Castle tests (eXceDt Roan) and from the whole series has been comuuted on the basis of results from the monitoring network. Since none of the stations were located imediately downwind of the test area so as to emerience fallout in the first day or two following a detonation, it is apparent that by far the largest fraction of the fallout, the “close-in” fallout, has not been measured.

A comDosite mar,for the comnlete series. showing the total of all fallout occurring through June 30, 19j&, 3rd decayed to July 1, 195&,,is shown in Figures 3.1 and 3.2. These maps contain the cumulative to+21 of all debris 3eoosited on t:y network from February 2& through June 30, 19%. T5e debris has extrapolated ta July 1 on the basis of the burst assignments indicated in Annendix A (except for fallout occurring after ?ay 21, w.hichwas reextranolated to Ya;lk.ee,see Section 2.6).

Isolines of activity were interpolated between stations and the average fallout for the wo Id was computed, by numerical integration, to be 9101: d/m/f\ 5 for a. total of 2.2.73 megacuries. 1

. . 3.2 TOTALS FOR INDIVIDWL TESTS--'---.--

To obtain t.hetotal fallout due to each of the individual tests, the following crocedure, was zsed. At each station, all fallout assigned to t:~ given b>urst,as indicated on the mars of Ancendix A, =s summed, and titetotal fallout values, in d/m/ft2 at 100 days after burst, were entered on a man. (For th?se comcu- tations, fallout occurrixq after May 21 was not considered, since there was some doubt as to burst assignment.) In the event that data were missing for an occasional day at a given station, the --missing values were estirratedby interpolation. If data were missing for a number of days, the sum ijas entered in oarentheses and indicated as a .lower limit of ‘activity. Isolines of activity were drawn and th? total fallout commuted; : by numerical integration. -

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__.._ ._._ f-1R i n I /

: 4- ‘T_ ’ ‘\ - / /Y. z ’ /, , -. i_ _ It-is not appropriateto comoarethe resultsfrom the,various testsuithout.first considering the timeperiods between tests. For example,fallout from Bravo was not masked by later debris for about 8 month in the region of tests, and could be identified for an even longerperiod in regionsremote from the test site, On the other hand, Union debriswas quicklyovershadowed by fallout from Yankee.,which occurrednine days later. The world.-widedistribution of falloutfrom Dravr,is shown in Figures3.3 and 3.L. Assignedto the burst MS all falloutfrom the period from February28 to April 5, 19%. with the exception of debrisin a limitedarea which was determinedto be from Romeo (SeeAppendix A). The averageactivity of this fallout,corrected t0 100 days after burst, was 1937 d/m/ft2, for a total fallout of h. 79 megacuries, or 3.74 megacuries as of July 1,'1954.

Figures3.5 and 3.6 show the total Romeo fallout from the time of the bursts through ~%y 3, 1954. T:ke2world-wideaverage activity at 100 days after burst was 1445 d/m/ft for a total of 3.57 megacuries, or 3.71 megacuries on July 1. tiedebris was assigned to the third burst, K’oon.

Fallout from Union (Figures 3.7 and 3.8) covers the period through May 12, a somew.%t shorter Teriod than the first two bursts, since Yankee was detonated only nine days after Union. The world-wide averagefallout was 28h d/m/ft at ,100days after burst for a total , of 0.70 megacuries,or 1.13 megacurieson July 1.

Yankee cumulativeresults are given in Figures 3.9 and 3.10.. : Debriswas specificallyattributed to t.ks burst t.h.rouph-?'b:;21; However, much of the fallout u!!ch occurred beyond this period also originatedfrom Yankee so thatthe.-total fallout is undoubtedly much greater than the,values given. Through iNay 21. Yankee fallout averaged 1219 d/m/ft for a total of 3.01 megac?lriesat 100 days after burst. CorrectLd to July 1, 1954, this value becomes 5.78 megacuries.

rjectarfallout is shown in Figure 3.1.1. Since this burst follower Yankee burst by only nine days, debris from !@ctar As identifiable as such only for a few days and in the regior: near the test area. This falloutfrom Nectar amountsto a uorld-k5<2 averageof 81 d/m/ft2, or 0.20 megacuries,at 100 days after burst, O.b7 megacurieson July 1, 19%.

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The smallpercentage of total debrisaccounted for by the observingnetwork is somewhatpuzzling. Althoughit must be assumed ‘that a large fractionof the activedebris was depositedin the b vLo%nityof th3 test site, it is also true that the shortcomings of the gummedfilm tectique, which have been ascussed in previous nsport~,may be responsiblefor the effect noted.

3.4 METECROLOGICAL mPRETATION

The total ,falloutfrom the Bravo test (Figures 3.3 and 3.k) clearly show the tendency for the major activity to rexain near the source latjtufie, mere seem to be no evidence that debris was carried ncrthmrd around tk uestern side of the Pacific high-pressure cell. L Almost no falloutoccurred in Japan,and very little on Iwo Jim from the Bravo test, The difference betweenthe two tests is a result of tk seasonal difference in L th3 locationand intensityof the"Gstern cell of the Pacific high. Tkds cell is almost non-existent,in the .mean,during the winter and i/._

- 33 - ea?ly swing, .whenthe Aleutian lows are farther south. As the western- cnJ1 of the Pacific hi& i otezasifies, more debris can be Carried towardths north, so that by the time oltb b&ee t&t (Figures3.9 and 3,101, in earZy &F&y,a larger fra-ction of the fsllout occurred in Jacan, Presumably, tests in the summer and early fall xould .result in the greatest contamination of the Japanese Zslsnds, while winter tests- would result in the least. Also during the winter months, nrecipita tion in Japan is at a . minimumexcept for a narrow zone on the western slopes. For most of Japan,maximum rainfall occurs during .the warm season,with the heaviestrains in June and September.

Similarly, in .other inhabited regions likely to be most affected by relatively early fallout, Nexico and Central America to the east and the Phillipines to the west of the test area, the dry seasonocc~s in the winter and the rainiest in the warmer months, so that here too, fallout would be at a minimumfor tinter tests as compared to other seasons.

3.5 HAXIM.U%ACTIVITY -AT INLjIVIDZA5 SEiTI13xS The bighest fallout reported on sampling day on an individual gummodfilm at each of the stations cf the notwork is shown in Figures 3.12 and 3.13, together with the burst responsible (figure in parentheses), t-he number of days after burst that the fallout occurred and the precipitation observed. All actitity Mlues are in d/m/ft2 corrected & sampling day. .As can be seen, the fifth burst, Yankee, was responsible for the 7Nghest a.ctiti.ty at most. of __. the stations. T5i.s is a result&t only of the fact that Yankee had the highest fission yield of any of the devices tested, but also because of the meteorological conditions associated with this burst. The high tropospheric westerlies were faster, resulting in a more rapid transport of debris towards the Americas. In addition, the winds in t.he eastern ?acific were from the west sout’?- west, resulting in tha passage of fresh debris ever ti-e $utlfcres$ern and southern states.

On the western side of the Pacif.i?, the normal seasonal increase in intensity of the western portion of the Pacific high-pressure cell and the retreat of the Aleutian low resulted in the transport of Yankee debris to-ards the Japanese Islands in the lower levels, although the direct trajectories at these levels moved generally eastward.

- 3& -

SECWET ActiPrty In exces s of 200,000 d/m/ft'on sannling day occurred at two s&ions in the hited States following t,heYankee burst (Billings, Mont., and Salt Lake City, Utah) and was a result of dry fallout at Salt .LakeCity and with rain at Billings. These. values exceed by an order of magnitude the r~ximum fa1Jotd reported at any of the Japanese stations and are larger than t:lemaximum values reported at many of the Pacific Islands much closer to the Pacific Proving Ground. (it,should be noted that it is likely that Kusaie, Ponaoe and Kwajalein received their maxim-m.act.ivity following t-heBravo burst',houever, these stations did not start gummed film observations until about two weeks after this burst and the values given probably do not reoresent the mximum fallout for the Castle series.)

-.3# - SECRET

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4 - .___-.--.

CHAPTER4

SPECIAL OBSERV~TIOMS 4

A series of special gummed film collections were made on Ponape, in tI_eCaroline Islands. In additicn,to the regular gummed film observations, (which were made at 0030 CCT daily at Ponape), a gurmnedfilm stand was placed near the windward shore of the island to attempt to sample air unaffected by local dust sources. No significant differences were found. Another gummed film stand was placed near the regular stands, but the film was changed at 12-hour intervals, in the morning and evening. On 11 days with heavy fallout, ths film exposed during the daytime hours collected. about 50% more activity tbn did the film exuosed during the night hours, despite tie fact t"latgreciritation was about equally distributed in the two periods. This my be a result of the nocturral stabilization of the very lowest layers of the atmosphere which in.hibitedthe dezosition of debris frcm turbulent eddies, although diurnal variations in the vertical tezerstlze lapse rate are small on a 13h-square-mile island in the trade wind belt.

To investigate the denosition ,ofdebris due to rainfall, rainwat r samples were collected by a 30-inch diameter funnel (4.9 ft 9 ) coincident with the exposure of the 2/~-hour films. The collected water was filtered at the end of each observation period -_ arrithe filter sent to New York, for analysis. Cn the nine days TAth the i-easiestfallout at Fonape, the totai collection on the rain filters averaged 56% as muchactivity as on the one-square-foot gummed film. During t.& month of June, when fallout has relatively light, the rain filters collected th-iceas much activity as the gin;nedfilm. This is again indicative of the iportance of the rainout Trocess ir, brinp,ing old debris (and Dresmabiy smlier cariicles) tc the ground.

- 38 - APPEXDIX A

---MAPS CY’ DAIIE FALLOUT ’

Maps showingthe daily fallouton the monitoringnetwork from Febmy 28 to May 31, 19%, and the averagedaily falloutduring tb month of June,1954, are appended. All valuesof radioactivity are in d/m collectedon a squarefoot of gummedfilm in a day, extrapolatedto 100 days after the burst. In most cases,two films were exposedsimultaneously and the valuesfor each are shown. Tk burst to which the debriswas assignedfor extrapolationpurposes is indicatedon each map. (See sec. 2.6 with referenceto burst ’ 'assignrmntsafter Hay 21.1

Lines delineatingthe areas of significant fallout (over 100 d/rn/ft2/day extrapolated tz 100 days after burst), labelled with the event believed respmsible for the fallout, are s:?own. The lines are’ dashed ti areas of greatest uncertainty.

The preci.Ditation which fell during each samplingperiod is shown in accordance w’,th the code given on t,he mars. Snm has ‘beer. reduced to its ua ter equivalent.

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