Operation Castle, Project 6.6, Effects of Nuclear Detonations on the Ionosphere

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TIMI clrrslthd or lltnlttd.ftatus of this reportrppliot Defense of the United State+ within the moaning of the . Its transm~sslon or the revelation of its contents

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contents in any manner tc an unauthixized SANDIA BASE, ALBUQUERQUE, NEW MEXICO :; ‘.

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Inquiries relative to this report may be made to Chief, Armed Forces Special Weapons Project If this report is no longer needed, return to AEC Technical Information Service Extension Oak Ridge, Tennessee

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Thie doaubnt condste of 75 pages, Report to the Scientific Director EFFECTS OF NUCLEAR DETONATIONS ON THE IONOSPHERE Evans signal laboratory SigKll corps libgiaeeriilg xdoratories Fort Ebnrnouth, Neu Jersey

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GENERAL SHOT INFORMATION Shot I Shot 2 Shot 3 Shot 4 Shot 3 Shot 6 DATE I March 27 March 7 April 26 April 5 May 14 May ( Unclassified ) Bravo Romeo Koon Union Yankee Nectar Bikini, West of Bikini, on 8argc at Intersection of Arcs with Radii of 6500’fram Dog (Yurochi) and 3 Statute Miles from Fox ( Aomocn). Eniwctok, IVY Mike Crater, Flcro ( Elugclab) TYPE Land Borgc Land Barge Barge Barge

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DuringOperationCASTIE,two ionosphererecorders were operated In orderto studythe *effectsof the detonationson the ionosphere. bimaal.data from existingstationsat Maui and Adak and specialdata furnishedby existingstationsat Guam and Okinawawere examimd for Severeabsorptionwas observed200 mileswest of all multimegatan E regionaftereach major shot was indicatedby the diffuseSporadic-E returnsatRongarik. Also, for shotsof megatonrangesan effeaton erationIVX was observed,its naturevaryzingfrom shot to shot. This phenomenonis apparentlyfar morecomplexthan originallyassumed, but it is stillattributedto the large-scaleconvectionresulting from the mnversion of blast-waveenergyinto heat in the upper&tmos-

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Thisreportis one of the reportspresentingthe resultsof the interestedin otherpertinenttest infomation,referenceis made to This sumary reportincludesthe following.&&rmation of possible general3nterest.t(1) An overalldescriptim of sach detonation, tcmation,amblentatmosphericconditionsat detonatim, etc., for the listingof all reportscoveringthe militaryeffecttest prcgram.

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Tb assistanceand cooperationof the foilowingindividualsand ed the operatim phase of Project6.6 in an outstandingmanner,dethan was required,so as to iusurethe success of tb project. Personnelof the Nationalbureauof StandardsionospherestatiaE IMt at the ionospherestationon Okinawa,who coopsratedso fully in the specialoperationof their stations. Standards,which providedone of the ionosphererecardersused and Signal Corps RadioPropagation Ageccy, which providedthe services which Okinawaionogramsreproducedhereinwere obtained. aided immeasurab*Zyin analyzingthe data and in writingparts of the. first draft of this final report. tive in the preparationof the figuresused in this report.

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Map ShowingLocationof Stationaand Approximate MinimumFrequencyDetectedat Site Ebr for Day of Shot 4, Comparedwith Normal Values. ......... RongerikFollowingShots 3 .;xd 2 and at Bikini Following Mike Shot (OperaAon,IVY),Compared at about 2 l/2 hr aftereach shot and also I2 Returns (lefi) and Shot 2 (right)by about 3 112 to 4 hr, Rcngerikat Shot 2 Plus 3 hr 49 rain, Comparedwith

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g 40hOtos55 ti, Shdng Mak: and Lrregular 57 to 70 zuA.n,Show@ Echo Risingfrm 350 to Showing Probable Smrioe Effect. ........ Showing Early PossibleEffectsand Startof

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The first objectiveof this experimentwas to firmlyestablish the cause-and-effectrelationshipsfor an ionosphericphenomencmfirst The secondobjectivewas to obtaincorroborativedata on effects at a greatdistance,first observedfor Shot Mike of OperationIVY, in orderto determinethe possibilityof the use cf such effectsas a mans of long-rangedetectionand to determinewhetheraq indicatim of the magnitudeof the yield could be cbtainedat distant‘locations. It was also anticipatedthat detailedstudy of 'W&h the local and the distantdata would providea betterinsightinto the machaknowledgeof the upper ionosphere. ztnvestigatethe effectsof the blastwave on the ion-densitydistributionin the E and Fl layersof the qonosphereand to studythe ab sorptiveeffectsoccurringbelow the E region. to rise to abnormalheights,and its ion density,tiasuredby critieal

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frequency,was found to fall belm normalvalues (seeReferenoe1). operatedfollowingat leasta dozen atomicexplosfons,occurringat than that of any previoustest explosion,it was concludedthat the effectwas a conseqwnce of ths nmgnitudeoftheshot. It was ream pcrrablemagnitude,confirmationshouldbe soughtand that, by locating two ionosphererecordersin differentdirectionsfrom the source,a betterinsightinto the mechanismmight be obtained, A possibleexplanationof the phenomenonwas given,based on the assumptionthat the blast-waveenergy,arritig at ionospheric heightsas a shockwave,was absorbedthere and convertedinto thermal energy,thus raisingthe averagetemperatureof a lare;eregim of the upperatmosphere,causingexpansionand risingof the heatedvolume. Ifthechargedparticlesweretomove inthe SW directionastbe neutralair molecules,the F2 layer would rise with the risingair mass, and the depressedcritical freqwncy wouJd be explainedby the doubt m this simpleexplanation;so a more involvedhypothesiswas of new ionizationdrift theoryhas made possiblea more-complete8xIn orderto testthe theorygivenfor IVY Bike results,it was at first proposedthat two ionosphererecordersbe so locatedthat propagationof the blastwave to the two operatingsiteswould take place acrossand slang the earth(smagneticfield,respectively*However9 it was not logisticallypracticableto obtainsuch locaticras. Atoll (aboti200 miles west of Bikini)were selectedas the best available locationsfrom which to obtainionosphericdata that might result .ina betterunderstandingof the phenomsnon. Gkinawawere interpretedas duetoan indirecteffectof Bike shot QI the F2 layer. From 'thetimes at which the irregularitieswere first tiatedby the blast,was propagatedhorizontallyin the F regim at a in ths rangesreportedby several This velocitywas shownto be withto have beentho firsttimethata

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ing for about l/2 hour,was attributedto abnormalabsorptionin the the shockwave and the consequentincreaseof collisionfrequency. This was observedfollowingShots Mike and King of IVY. It was ccneludedthat this absorption,thoughsignificant,would probablynot Initiationof effectsin the E region,due to local changesin Bikinifor Shot King, which took place at Eniwetdsand which was relativelysmallctxnparedwith Mike and the majorityof the CASTIE to followatomict3X@OSiOIl8. This appearsto be anotheraspectof the effectsdus to localchangesin iou density,as it seemsto be increasedbackscatterfran a regionthat is "roughened"by turbulence.

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quenciesof the layersof the ionosphere.,Transmittedpulsesof by the equipment~tbeirwturn, tbstraveltime Lndicatingthe rangeof 1 to 25 megacycles. The frequency is sweptthroughthe dicatedhy the frequencyabovewhichthe s&&L penetratesthe layer, thusproducingnoreturn,andisa measureof the maximumelectron oscilloscop trace, showinglayerbight au a functionof frequency. cussionofthemethodandofthe interpretationofthe photographs designedto radiateand receiveprincipallyin the vertlcaldirecticn Scheduledoperaticpof the recordersat bothMarshallIslanda ataticnebeganseveraldayspriorto the firstshot. It ccmtinuedin wards,the recorderat Rongerikhad to be startedpriorto each shot and left to operateunattended,at one sweepper minute,untilthe filmortbe gasolineinthe power unit ranoub. Atbotb stations,a sweeptime of 15 set was used,the entirerangeof frequenciesFran 1 to 25 megacyclesbeingcoveredin thattime. In the programwhich obtainedin the courssoftestandmaintenanceruns.)

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Dorml operaticat Guamio fivetimesau hour (as in Secticm Normal operationat Edak+ fivetimesan hour (as in sectica aud at 3 aud 30 minutespast). .

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DATA AND RESULTS The attemptto achievethe first principalobjective-verffizAwrtlcally "YrrPsmittedradiommes until 7 or 8 hoursafterdetonation. The absorptionitselfthus becomesan importantphenomenon. at SXe Elner is apparentin Figs. 3.1 and 3.2, original?.yprepared b!inimumFmquenc3-Detectedat Rongerikfor Day of Shot 4,

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for the field report on Shot 4 alone, but used here sincethese cgrves typm all shots of wry large magnitude. In these figures,the minImum frequency reflected from the ionosphere and detected at each station is plotted against lccel time,using a light line. The standard symbol “Bll is used to denote times when complete absorption apparently prevented any ionospheric return; occasionally, for very brief intervals during these periods, an extremely weak signal was perceived, hence the symbols are locahd in the vicinity of the R-eahile it is true that there are other factors Influencing the minimumfrequency value, it is prfncipally a function of the degree of curves of Figs. 3.1 and 3.2. The trend of these curves indicates that the minimumdetected frequency is greatest when the sun is highest and the absorption bhich is due to the icnizing radiaticol from the sun) is Unimumdetectable frequency, day of Shot 4 8 8 e B Ditto - occasional values during periods di otherwige comflete absorption lhx and min observed values ceding and following Shot 4) Fig. 3.2 - L!idmum Frequency Detected at Site Elmer for Day of Shot 4, Compared with Normal Valma ‘

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The lateabsorptiwaeffectsof Shot 4 observedat Site-Elmer there folMw*g Shots 1, 2, and 5, but not 31 as shown in Table 3.1. This table and the correspondingTable 3.2 for Rongerikwerecompiled from a thoroughexaminationof the scaleddata. Althoughtheretias> definitionof %mmal" and to sme erraticismof absorption),Tablets to have been strikingsimilarity,for all four very large shots,in the eudlngtime of completeabmrption at Rongerikand of the renewedabsorptionatElmr,as well as inthetime ofreturntonormlminimum frequenciesat each location. ww 1 Ended Bogan 1 Ended * Equipnt failedat plus 3 h 45 m - absorptiat.stillpxvsent.

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One difficultyarose in interpreting.the early abaorptiont thew was a weaknessor completelack of echo tracesover the entire . frequencyrangeduringearly morninghourseven on daya when no shot took place. This has been attributedto a combinatiauof low restate that, on shot days, there appeartohave been three periodsof ably be attachedto each. Pirst,due largelytothe equipmsntinthe signalintensityto fall below the thresholdof detectability. Since this coincidedwith shot time, it accountsfor the beginntigof what was calledcomplete"absorption"ccauingjust beforeor aftereach shot. Second,an effectconnectedwith the overheadarrivalof the shockwave in the lower ionosphericlayerswas expectedto startat aboutplus 15 min at Ronsrilcand aboutplus 20 min at Elmerfor shots. at Bikini. This effectis the increasedabsorptionof radio signals 3.2, it appearsthat this effectlasteduntilabout plus 35 min at Rongerikand somewhatlongerat Elmsr (whichis about 50 miles more . distantfrom Bikini). The third periodof absorption,which.seems 1, 4, and 5, and an indeterminatetime after Shot 2. It lasteduntil tion of this protractedeffectis given in Section4.1. The lengthy Site Elmer, may be attributableto a similarcause. In commonwith real*ltaof previousionosphericexperiments activityoccurredfolloviugall shots,as evidencedby the data taken at Rongerik. At Elmer,the data were very scantydue to abaorpticol there were sinilarto those above Rongerik. In orderto obtaina quantitivecomparisonbetweenpost-shotand normalspot-adic-E.conditions,the graph of Fig. 3.3 was plotted. The freq\llency(fzsjat Rongerikfor three weeks prior to Shot 1; it ia ponds to ths averagezero time fc:*Shots land 2. Curvesfor Shots 1

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TIME FROM ZERO (HR) FromFig. 3.3 it is seen that the highestsporadic-EfrequencLes , then came very near to normalvale by plus denly attatiednear plus 4 hr for Shot normalas the others. 3 i; not as much abovendr as lcag above This shouldnot be surprisingin view of the smallrelativeyield of Shot 3. The amountof data is instificient to be conclusive. normal even before the shot. occurredon a day when frequencieswere above_

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For purposes of cornparieon,an ionogrm for a normalday ie To Illustratethe unusualnature of the sporadic-Eeahoes ob sent+, each arrangedto be read from top to bottcnt,startingat the left,with the elapsedtime from zero indicatedin hoursand minutea. Shot 1 flu (see Figs. 3.5 and 3.6) 34 1/2 D& - firstvisibleecho of any bd afterthe shot; Es at llo km

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a picturetypicalof this periodshowinga strong lower boundaryand considerablescatterabove dicationsof Flat 200 to 300 b, 3 to 4 mc) min - Es continuesstrongbut Fl is mseenn through cudinaryare clear but %qreadn)

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2 3 4 6 6 IO 14 UC 2 6 4 6 6 IO I4 YC 4 I&C), very weak due to abempticm "spread"EB echoes, emwhat strongerbut still hour periodcentemd here .

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faint traces of Fl am near 4 mc) 23 min - aev8rallevelsof Es includingone at htgher tyrn; (ES continmd unusualfor 45 ndn more) Fig. 3.7 - Ionospheric Recordsat RongerikFollmringShot 2 by 39 ti

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separately,exceptthat Shots land 2, whichproduced prapoaeesucha pl%FJeAt&imlismore usefulthanourms pluttidagainat timeof day;it is alsojustifiablebecauseeach of the threeshots Mona inths F2 region were similar.)Ineachcase, the virtual height of the layx-rose to wellabovenormaland returnedto normlat a similarrateand aftera nsarlyequaltlm interval.LIkerise, the aftereach shot. Thus, the F2 regionabovethe Rcmgerlkstation, Completeabsenceof returna near shottimehas been attributedto arrival of tbo shockwavein the lowerionosphere(seeSection3.1). which the F2 lapr begantoappearIn the ionograms.

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ELAPSED TIME AFTER DETONATION (HRS) FollowingShots land 2 and at BikiniFollowingMike Shot

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top two lmograms of Fig. 3.10)we:-mak'e&iioesappearing-Anscatreaordtothenext. TheP2e~hoescontinmdtobe irregular end er raugeof heighta.Therewaoa prevalenaeofreturneinthe region 'betmn thms two mgiclllspossiblyobuque or the extraordinaryray, withtwo shortperiods scalable somwhatsoonerin the caseofShot lcladensityat two levels,bothextraordinarilyhAgh,withthe ion deneltyof the higbr etratumgmaterthanthatofthe lower0 Under Au accuratecalctit&m of the electrardensitydietributiaa implied by the sha:m of the cume in suchionogramsio ~saible, but diatributicmwhichmighthavebeenpresentbad the d&muptim not t&ma $lace. Discussianof the iaa movematwhichmay havecausedatmh not simultaneouslypsent in earlier recorde (ae fb F2 layer was dm to horizontalinhomogeneityand generalirregulerityof Ate ian

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Thisia known 88 a “C ccmditicud Xt should be noted that the G cmditim adduced here does not indicate any major dlfffmenc9 Wxeen the effects of IVY Mike and CASTIE1 and 2. It my be seen From Fig,. 3.9 that, during Operaticm: IVY, normal valwm of F2 critical frequency were much @eater than during the first mnth of Operation CASTIJL The Fl critical fxwquenciee, however, were of the same order for these two perioda. Ccmsequen+.ly,uhlle observatim of the F2 layer may have been L. Pmpossible following CASTIZ1 and 2 because of a G comlitlca, a comparable depression of the F2-layer critical frsqtrency %ml.titg frm IVX Mike would not have been sufficient to cause such condition; Figs. 3.13 and 3.34 give, for Shots 1 and 2 respectively, sequences of iouograms showing t’le deecending virtual height of the F2 layer as it returned to normal. There am indications of obliqw returns, partiaularly in the last picture of Fig, 3.l4, epidenohg effective layer tilt. No effect QL~the height or critical frequency of tb F2 layer was observed after Shot 3. This is consistent with the inferace drawn fmn Cperation IVY that the znininnmenergy release required to produce the rielngQ2 phenomenonla apparently mater than l/2 . was less pronounced than that observed ftioulng F2 layer ~19sobservable almost ccmtinuously after the absorptlcm that has been attributed to the effect of the shock wave 0~1the D-’ .’ ‘. region had abated. Scaled values of virtual height and critical frequency are shown In Fig. 3.&. Also plotted for coaparism eta mnriwua,minimum,and median values of data taken over a period of ehot, v prim to tbs shot. It may be seen that, following the ual helets were consistently greater than the height UA NGCondition* is an lcmospherlc abmrmality, observed occasicmally in all parts of,tbe rorsld, usually asaoc1ated rjith a amgnetio &arm. The condltlou is s’%mplythat the maxivmmdeneity of the F2 layer (as nmaeuredby its vertical-incidence critical fmquency) is equal to or less than t.hat of the tier- Fl. Rben an analyst finds an lonogram ?A which the Fl layer appears and the F2 layer does not, he mqects a G conditloa. Homver, posative identification la lnade only after studying records taken imediately preced&g or following the suspected condition. If these records show an F2 critical frequency just gmater then the Fl critical fmqusncy, a trend ia establishsd and it is a safe asaumptim that a G condition existed.

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clear evidencet of obliquityappearsin Fig. 3.18, partIc~Iy in the of a retumto mmal (atplua 90 and.%,&). AI ZDz&rated by of this period, the lack ofacmiatencyfrm~ca~ mintrtetothenext _ fmmmotim oftbe air molscules. \ Despitethe imegularltlea,an attemptaas made to analyzethe \ dab recardeddurkrgthb period. Ranges of'_heightand freqymcy valtresforthevariousgroupsofechcea tithe F2 regicarere plotted 70 min, Show-Echo Risingfran 350 to 500 looApparent

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heightto risewas notedin eeveralsequentialgrasps. Coneleqtlently, a plotwas madewiththe minimumheightof each'grouprepresentedwr cro8a(Fig.3.19). A possibleexplanaticafor the increasingheights wa8 immediatelyseen. The hypothesisis that the risingsequences ing horizontallyin somzdirectionawayfkomthe operatingsitea8 partof a radialmotim originatingabovethe explosion.(TIManten-, eredwhenhorizontalinhomogeneitieszre presentIn the ionosphere. The %eight#at which suchechoesappearis greeterby virtw of the“ greaterpathlengthand is, hence,called"apparentheight"in Fig.

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Fig. 3.19 - ApparentW.nimumHeightof Groupaof Echoesat Rongerti Assumingthat the point of reflectionmoved horizontallyat'a heighth with a velocityvg passingoverbeadat time to, the slant xnge Rattimetxnaybe fomdfromthe right&triangularrelationship of the seqtxmcebetweenplus 40 and 70 min, it Is possibleto es%+ lish valuesof h, v, and to whichfieldthe first hyperboliccurm shownin Fig. 3.19. Equation3.1 may be solvedfor h, vs end to in

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In Fig. 3:19),it appearedthat a similarheightvariationoccurred curve in a positiontranslatedjust 15 min to the rfght (later)producedan excellentapproximationto the crosses. A fu&her tranalefim of I.5min again resultedin a good fit, but over a smallerregion; as is evidentin the Figure. The line approxinatingthepoiatsafter plus 85 IIIJ~was fittedmerelyby eye, and is a duplicatim of the carrespondingportionof Fig. 3.15 on a deferent scale. The &roup As may be seen from Fig. 3.19, the firstcurve,which was obtainedusing the values of Equaticm 3.3? agreeswell with the trend of t,hecrosses. From this it appearslikelythat,as hypothesized, therewas a horizontalmovementof ionizationat a heightof about about45 min after Shot 4 was detonated. …