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<br />!
<br />
<br />c!ocumentation. Nucl~i.. ~wmp!.~(! in the upper portions
<br />t.>~ the first cloud were 3un.d.y nbovlo: noise level.
<br />TllO:3e in the :iecond clout! w~ r~ un order of magni-
<br />tuce above ~ackground with ::t ,i.gni f lCiltlt ic~ crystal
<br />co:'c~ntration::i pr~sent at thl1 ::lame r:lme.
<br />
<br />
<br />_~ oIoIllI"""',."".....
<br />~.;:tfIU c..""Il'l'.....lIQff
<br />
<br />. ~...
<br />t;
<br />~
<br />
<br />,
<br />
<br />j 40 ,.
<br />.r ::/ ,~O~:
<br />
<br />~.""~/ ,,10 l.t .-0'" .......... 1O.r
<br />~ f- IV.. / . ,..--- " ::..f.
<br />! f- -\:; \ f /...... " [ti
<br />!.c ;\\\'-,;~, /~) ~
<br />I .. ...\ ' \ " "'1
<br />r ~\ ". .', "\ / /
<br />,r.. =1 ....''''-', ,,/ ,/ ,
<br />g ~ "'-" \. ''''... - ,,,,,/ . "J"
<br />~ i-'~", "'" /"". //
<br />'r ...... ---' // .
<br />~......J\o;"'.~ ~-~./ __,- J
<br />~ , : ;"-:v"".':-'-;r"'-'~~v:v~{~ J..2-
<br />KOO eo 1100 u IlJ '4 2J U 10 M 40
<br />,.... ..,.
<br />
<br />~igure 2 J\n altitude-tim~ diagram of the flare-
<br />seeded cloud 2 on 27 June 1976 show.lng
<br />cloud boundarie9, alrcraft altituces a.nd ice con-
<br />centrations.
<br />
<br />,\n altitude-time diagram illustrating the
<br />24 July cloud 2 case :ls presented .In F .lgure 2. The
<br />quasi-horizontal lines represent: the cloud top and
<br />base and the twO aircraft tracks and their sample
<br />times. All interpolations and extrapolations of
<br />ice concentrations away from the sampling levels
<br />art! obviously crude in tllis figure and below in
<br />Yigurt! J. Uecelerator- :ilide 9c.lmples of the cry-
<br />stal~ showed concentrations about 1.11 times hi.gher
<br />thAn the IPC data, and with some degree ot aggrega-
<br />tion. ~ost crystal types observed, th9ugh planar
<br />and small, are best described by the 1.1 cla::l::i of
<br />~!agono and Lee (1966). The maximum precipitatJ.on .
<br />rate at cloud buse wus O!J,gCI'Vcu 25 minutes ufter-
<br />sc~ding. !he snow shower consisted of centlmetcr-
<br />s!.zed aggregat.es too large to be mt!a::lur~d by the
<br />,P~~S instrum..::nts on the C.LOUG base aircraft. Ice
<br />!1uclei 1:""0 ord~rs or magn ltude above bac~<ground
<br />.....ere obs~rvel.! on one f.!...!.ter which was exposed at
<br />cloud base from the t.Lmt.;: of scedlng until just
<br />after tile ?eil~ in precipitation. 1'he filter
<br />~xposec for the remaindc.r of th~ exp~rime.nt also
<br />showed nuclei well above background concentrations.
<br />'t-~~llsurem~llts oE the InJ.tiul latct'al ::Iprlluu.ltlg riite
<br />of: the glaciated port.l.on or the cloud showed it to
<br />bc about the same ll!:l the updr.aft varIllnce measured
<br />~y the uppt:r aircraft. The: resulting ice'c.loud
<br />""as revisited 70 minutes after seidiug and found to
<br />~1.:\Ve only about '. ice crystals ,Q.- remaining.
<br />
<br />5. DISCUSSION OF THE AgI-NH4I CASES
<br />
<br />The results of the base seeding experiments
<br />are presented in Tables 2a and b. Five base seeding
<br />cuses in w!\ich no resultJ.ng Ice crystuls were detect-
<br />~d before ~he end of smn~'llng are also mentioned in
<br />Ta1.J!.e 2b. '~'he average updraft needed to raise the
<br />Ag ~ to the sampling level ls cOllllHlred to the average
<br />updraft observed at base from the dotg aval1a~le
<br />w.lthin + 10 minutes of the t.lme of seeding. In four
<br />'of the five cases with no ice detected, the average
<br />updraft was insuffic.lent to car-ry the seeding mater-
<br />la.l to the ict: crystal sampling level. In the cases
<br />
<br />that had ice crystals ~etectedl the:: ~yerage updrafts
<br />obscrv~d at base ....ere: ....1th1n 0.2 m 9 . of the
<br />r-~quircd values.
<br />
<br />The 17 June cases 1 and 2 in Tab!e 2 are
<br />comparable. Bot.h !.nvo.:'..vt: thill (1.:2 km) ~tratocum1.\lu9
<br />dec~(,g dominated by a strong !.nVl::r'~~on. Thc upper air-
<br />craft almost alvays recorc!..;:d ~c~cdldlng cloud above
<br />the lnve r510n. '!:!lOugll t!li: bu~~ upr~ rafts !lUd an ade-
<br />quate strength, all the sampllng (DC lee In cl\lud 1
<br />occurred above the inverslon lev~J.. It is not known
<br />if crystals existed at :ower levc.:'..s. In case 2,
<br />iilu.!Jtrated in Figure 3, ice cry~tit"!.s w(:rc not. round
<br />1nit.ially in the cloud. They wcrc ruund .!.at:~r near
<br />the. bU!::le of the fnver-sion ju:;t before cloud glacia-
<br />tion was visi1.Jle':'l Even though t!l(~ average observed
<br />updraft. (0.3 m s -) was 'Jeakcr t'I.:'H'I In ~1c f.!.rst
<br />clouJ, only an aVerage of about 0.5 m 9 was needed
<br />for the main pu'::'se tll rese!\ tht: sLlmpling level in
<br />the time availa!>le. !WO initial \JhLsps or ice were
<br />obse rved early in the exnerImen Co The fJ. rs t '"ould
<br />have required a 2.5 m s-l upJrafc to hav~ been
<br />as::Jociated with seeding. Values that hig!1 were
<br />obs~rved among t~e 5-s 'eve'rage.g~...a,~', ba..9.t: J lpl,though
<br />the pass averag~s ....ere much .Lower.
<br />
<br />--''' Cl_ __. _...1 UI."__ "'1_-
<br />
<br />_ ..I __I. .11.... u.........
<br />:'::: :.:.:: ~::'; ~:;!Il ":J~:"::7 tc:;:;:7:/'I_~:~I.. ::!!;,.
<br />
<br />1rM~:"
<br />
<br />..1_"- _..u... ._u_. ...11 ....- _..I. ~~:. 1111
<br />
<br />0.1.) .::: ~ ::~ :,11
<br />
<br />nJ..I, I t)
<br />1.1;1.1 ...I~.
<br />..1....1..
<br />
<br />1,1110"
<br />I,'. lull
<br />
<br />_t.. .~:: i ::: :.11
<br />
<br />,.1110"
<br />
<br />J,t.
<br />J.I.:I,I.
<br />
<br />I '....1_ 11_. ...,. _. _' I._II
<br />
<br />_rrM....LI...... ,...1.. c......
<br />
<br />D.t.
<br />l~"
<br />
<br />"...
<br />-,
<br />
<br />.... u-p,.II.h ...... ..._.....
<br />......"..1..... .... ...~..,.,.,
<br />
<br />11,011."
<br />
<br />I'J.....
<br />
<br />..,
<br />(-1,1..,,,,
<br />
<br />..,
<br />1.'1
<br />
<br />I.'
<br />
<br />U.) ',I
<br />CU.ll.I,I.I,..II)
<br />
<br />...
<br />11.1."IOI.l,ull)
<br />
<br />,..
<br />(l,il.to"...II)
<br />
<br />The main ice pulse was finally penetrated
<br />by the upper aircraft ct;::scendlng further i.nto. the
<br />cloud. The lower aircraft observt:G .lts pt::ak precip-
<br />itation intensity shor,;~y aftt:Nu-r,!s and rt!pc'!'~ed
<br />the preclpitation to be r~achJItg. the grouud e.!: the
<br />1 km level. 'TI'Ie tota~ time from ~~edJng to ':.~'e
<br />tnllx.lmLlln preclp~.tatlon rate at cloud busc WHt! about:
<br />35 mJ.nutes. 'fhi::J is long compared to the 25 ain-
<br />t1te~ in the 24 June c:"oud 2 flare case and ,:he 21 .
<br />minutes in a similar CO2 case; it.'reflect~ t~e
<br />delay nec~ssary for th~ material to ris~ to activa-
<br />t.lan temperature leve~s.
<br />
<br />The effectiveness values for this an~ the
<br />other acetone-AgI-~H41 case~ oE Tal)le 2u ar2 plotted
<br />1n I"igure 4; t~ey arc close to t!lt~: laborator-y curve.
<br />The cold end of the temrerature error bar i::l for the
<br />cloud top in t~le 17 .June ca~e anG for the p.lume tlJp
<br />in the other cases.
<br />
<br />Cloud 1 on 29 July gave two estimates of
<br />AgI effectivenes::s. l..n initial pulse ~f ice was
<br />observed early and reouirec a 1..2 m s uodraft, an
<br />average value found o~er about a !~~.ilomet~~ di.stance
<br />j.n the updraft core at the ::start of. seeding. The
<br />
<br />\,
<br />
<br />,.
<br />, .
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