WMOD00483

• Title: Microphysical Observations of Winter Clouds Over the Southern Canadian Rockies
• Weather Modification - Doc Type: Report

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Particles and hydrometeors are Measured by
four probes from Part ide Measur in 9 Systems
located at the belly position. These include:
a'l ASASP (aerosols 0.1 to 3 um), a FSSP probe
(cloud droplets 0.5 to 47 urn), a 2D-C probe (ice
crysta 1 s, 25 to BOO urn), and a 20-P probe
(precipitation particles 0.2 to 6.4 1lI11).
Position keeping is accolllpl1shed using a Litton
inertial navigation system. Instrument data are
sampled through a CAMe llDdular interface,
managed by a computer based system and are stored
on a s treami n g tape dr ive. Data ana lys is is
perforllled on the ground using a VAX 11/780
computer. A IIOre complete description of the
aircraft system is given in Cheng et al., 1986.
The aircraft system configuratron---remained
essentially the same throughout the three field
programs examined here.

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2.2 Cloud Microphysicll Cli..tologies

A summary of the microphysical
measurelllents made on these eleven days is
presented in Table 1 for ,all Olin-cloud" data.
"In-cloud" data points were identified as those
one-second values where eithe3 a droplet
concentration greater than 10 cm- was measured
by the FSSP prob, or an observation of ICC
greater than 1 L - was indicated by the 20-C
probe. L i qui d water measurelllents were derived
fro~ FSSP probe data for all cases except for the
February 1984 flights. For these cases, the J-W
probe was used for liquid water measurements
after instrument problems with the FSSP precluded
quantitative measurements.

The values in Table 1 represent the
arithmet i c avera ge of all Min-cloud" one-second
data avera ges. Inc1 uded are the f1 i ght date,
number of one-second "in-cloud" samples,
environmental temperature at measurement level,
liquid water contents, ice crystal concentration,
ratio of liquid water to ice crystals and mean
ice crystal diameter. Also noted are estimates
of the cloud base hei ~ts and base temperatures
representative of the clouds. The liquid water
to ice ratio expresses the amount of water
available per ice crystal and has been suggested
as an index of "seedabil ity"

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(Heggll. et al., 1983). Higher ratio values
indicate ~there NY be sufficient supercooled
liquid water present for introduced Idditional
ice crystals to grow to precipitation-sized
particles.

Cumulative frequency plots of all the
one-second liquid water and and ice crystal
values were also plotted for the aggregated t'ata
sets. These plots have been presented elsewh!re
(Barlow et al., 1985) and will only be noted
briefly here. The results suggested that cloud
liquid water values in excess of 0.1 9"l-3, are
relatively frequent. These plots indicated that
over SO\ of the liquid water values recorded
during each of the three field seasons exceeded
this value. Average ice crys\al concentrations
are close to or less than 10 L- for ~st cases.

As indicated in Table 1, the combination
of relatively high liquid water values compared
to ice crystal concentrations yields hi gh
"seedibility" ratios as indicated in the tables.
Average values for these are on the order of a
few hundred and suggest, according to a minimum
benchmark of 10 (Heggli, et al., 1983), a
"seeding potential.. ------

The preliminary results of a llDre detailed
analysis of aircraft data collected on
February 9, 1984 have also been examined. A
total of 17 cloud penetrations were Nde during
f1 i ghts on tM s day. These lIleasurelllents were
made near the upper edge of a stratocumulus deck
that extended across the divide and became llDstly
broken to the east. Cloud bases were
approximately eleven thousand feet (_130C) with
tops lIpproaching thirteen thousand feet (_140C).
The relative frequency of occurrence of
ten-second averages of "in-cloud- liquid water
contents is given in Fi gu:fe 2. Over 55~ of the
values exceed the 0.1 9"l- minimUM for a seeding
potential cited for the Sierra Mountains (Marwitz
and Stewart, 1981). Ice crystal concentrations
were all less than 10 L-1, commonly around 1 l-l.
This combination of available liquid water and
low ice -.:luld suggest that many of these clouds
would meet the microphysical criteria for being
"seedable".

Summary Sut"tk:a tor Each Flight
Temp LWC LWCIICC Ie Cloud Bale Cloud Base
Flight it He ICC CItg of water Diem Height Temp
Incloud (deg C) (g/m') (111 ) per crystal) film) (kllot"t) (deg C)
830315 4127 -19.0 0.17 10.5 ~11 411 10 -12
830324 2303 -14.4 0.34 1.0 1264 397 9 -8
831209 2805 -19.9 0.01 5.6 13 533 7 -13
831210 3777 -1,3.6 0.22 3.0 722 295 7 to 10 -610 -13
840201 919 -19.2 0.05 1.9 199 330 8 -8
840208 1408 -9.9 0.10 1.1 409 150 11 -7
840209 2903 -13.0 0.11 1.8 470 309 11 -13
840210 2737 -18.2 0.06 1.3 1137 394 8 -8
840211 3389 -17.1 0.01 10.1 S46 320 6 -6
840212 4451 -9.9 0.02 11.0 61 323 5 to 11 o to -10
C.. 840213 2222 -12.8 0.09 54.0 52 86 10 -9
Tlble 1. Sunmary statistics of "in-cloud" lIicrophysical characteristics for each f1 i ght.
Included are averages of cloud supercooled liquid water content (lWC) , ice
crystal concentration (ICC) and mean ice crystal diameter (IC Diam).