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298 JOURNAL OF APPLIED METEOROLOGY VOLUME 29 at 4-min intervals. On the 20 min pass the droplet dis- tribution had broadened considerably with mean droplet size now between 15 and 20 J.Lm. Liquid water contents had increased to 0.15 g m -3 at the seedline and to 0.5 g m -3 near the seedline. The 2D-C and 2D- P images showed smaller particles with some images indicative of water drops up to 100 J.Lm in size. Rauber and Heggli ( 1988) have presented cases in mixed-phase clouds when water drops of this size were sampled by the 2D-C, and indicate methods useful to deduce the phase of small transparent images on the 2D-C. The evidence at P3 + 20 and P3 + 23 is similar to that presented by Rauber and Heggli when large water drops were present. Compared to other regions of cloud, rel- atively high concentrations of droplets 19-25 J.Lm were sampled within 1 min of these two penetrations. The highest water content of the 1800 to 1840 flight segment was observed at 1821:30 by the CSIRO probe, 0.48 g m -3, while liquid water content measured by the JW probe on the aircraft (not shown) were half those of the CSIRO probe from 1814 to 1840 indicating the presence of droplets > 40 J.Lm. A summary of these penetrations of P3 is included at the top of Table 2. The dispersion for P3 is calculated assuming the ice observed near the seedline nucleated at the time of treatment. The 2D-C and 2D-P images are shown in Fig. 6 for times of P3 penetrations. Note the change from den- drites and aggregates of dendrites on the 12-min pass to fewer dendrites and more small spherical, transpar- ent particles (examples are indicated by the arrows) on the 20 and 23 min passes. As indicated above there is strong evidence to suggest that these images are water drops 100-200 J.Lm. On the 28-min pass a distinct in- crease in ICC composed primarily of particles < 200 J.Lm was observed near the seedline. This is apparent in Fig. 5. Compare the 2D-P distributions at 1826 and 1831. The images (Fig. 6, and others not shown) in- dicate that these particles are small water drops, rimed columns, needles, and small graupel. This rapid gen- eration of ice, unexpected in a placebo case, was likely the result of a secondary ice crystal process that began around 1815. Note from the FSSP data in Fig. 5 that 20-25 J.Lm droplets were observed at 1814, 1822, and 1826 on the edge of the ice region. Droplets this large were not observed at any other location. Also recall the increase of small ice particles at 1822. The broad- ening of the droplet distribution and the presence of large drops is consistent with secondary ice crystal pro- duction (Hobbs and Rangno 1985). Natural ice gen- eration processes such as these complicate the differ- entiation of regions of high ICC caused by seeding. P3 + 0 2D- C j- j. j lSx ,l. r ,rJV t!Pt.~ r j r r.c.I ~ ~ J: t j j.l !.j .l~ f ,~~) J'!'.~ 2D-P ,r~~l. r1.rtjn)'~Hi~)jllltr Ilr)LJ)~j' IIjf.jrrr~~i* it r jl~jrl.JJ.j~j"~I"'r~ltJ~ ~UJf...rJ'lh~nnhtrk.~rr~LJlrhkj~~~Jrn.rj~. P3 + 12 2D-C H 0.8 mm .,. - ~ t r .L J-j' ,~ r r )- J r .r r rr r t ,~ ~ Jilt j- j' r J J r ,~ \", r ~ 2D-P H 6.4 mm rn.~~r~n.nni~~lrt~~ff1rrftrlrjl.rj)r.~Lrlrrr~)~rrrrr)#r'I.~j~Ir~ILljfrj}~f1~nl*j"J..J~t~~rn.~i.J-tH),T P3 + 20 2D-C oJ- oJ- oJ- oJ- 1 ~ t-. J ,~ J .I.l j r ~ i r J J ~ ~ j J r ;.. .rGJ' t r ~ ~ t t r ~ J !' .~ l- !' r r f ~: ~ J r r .~ ~ r 2D-P I'r Jfjr-)nJ'f1rtfl~~l.Ji Lfjl~~~m Ilr/.Hj"JI" rJr )'"r~~))t~fj~rrlf r~j'~Jj.~hrll)'~rrrrH~itrlirrl H~~nHif}/. rj"rj'jHj'j.~~Jj. J'ftf rrl.~t P3 + 23 2D-C , f L .L !-.. f r ~ J' ,I' j t r ~ .1 ,l... ~ ~ j r .u f ~~ r r .1 ~ ... ,L.. ,~ r ,~ .. .. .l !It j. ). !~ j. f }m1n~ rlITi~rnrr~UI'~I,HHl(~/r)nl.l.y jmrr~mfh ilMnlm rTI.jJ/Hlllln I.IIllt Ilr~HjJ i'ljlllrrj~hllrJHI.})"j)jlf))'lr~rlmrrMt ~HljJJ II. P3 + 28 2D-C . r ,l r r ~ j" f" r .L... I ~ .L ).. r j" r .. [ rr ~ J J ,I ,I !-.l !... r !,I- .I ~ . j'" ~ ~ j- f !J 2D-P II j~)JIJlm l)jllrllJlJlllnrrHf jf j~)JJ)JJjjjJ~)Jmjl).rjjJj/)jll)jWjJI.IJr rJJjjfWI/IIJJW))llfmtljffIIIJJIJf l~jljJjltIJ )~f.f1Jj)ljJjjjJJ~JJJJHlfjJJlltIJjJJtfjjjJJt ))J)/lrhIJ/}ff} III~~ FIG. 6. Images from the 2D-C and 2D-P on the research aircraft during penetrations of P3. The bottom row of images in each pair is the 2D-P.