WMOD00288 ‎(3)‎

• Title: Atmospheric Tests of an Organic Nucleant in a Supercooled Fog
• Date: 12/2/1989
• State: CA
• Country: United States
• Weather Modification - Doc Type: Report

The P. syringae nucleant was dispersed as a fine
powder from the front window of a Cessna 421 aircraft On
two test runs of 3 to 4 km in length. On the first run, 10
gms of nucleant were distributed, while on the second,
about 100 grns were released. Following each test run, the
King Air 200T cloud physics aircraft flew tracks within the
fog that were orthogonal to the original seeding track. The
flight track for the second case is shown in Figure 4. The
tracks of the seeder and monitoring aircraft, moving from
north to south, coincided until 102450 PST, when the
Cessna aircraft entered the fog for commencement of
seeding and the King Air aircraft began a turn to the east
to setup its monitoring runs. The rest of the track is that
of the King Air, as it crossed the seeding track five times
for measurements.

A summary of the pass measurements is provided in
Table 1. Note that fog water contents averaged 0.20 to
0.25 gm/m3, the mean (averages over 6 sec.) maximum
droplet concentrations ranged between 100 and 150
drops/cm' and the mean (6 sec averages) droplet size
ranged between 10 and 17 JLm. Natural ice in
concentrations of 1 to 2 crystals per liter were encountered
in the undisturbed fog near the time of the test runs.

Examination of the 2D-C entries in Table 1 suggest
that the light seeding rate (10 gm over the test track) of
P. syringae produced no detectable seeding signature.
There is no evidence of increased ice crystal concentrations
during the four monitoring passes that began about 1
minute after the release of the nucleant at 100833 PST. Ice
is present with mean (5 sec averages) sizes 50 to 100 JLm
during all passes, but the concentrations are low. If there
was a seeding signature, it was missed by the monitoring
aircraft.

The entries in Table 1 suggest a different
circumstance for the heavier seeding rate. About 5 minutes
after release of the nucleant at 102450 PST, maximum ice
crystal concentrations of 155 crystals per liter were detected
as the monitoring aircraft traversed the test track. Mean
particle size at first penetration of the plume was 85 JLm.
Six minutes later the maximum particle concentration had
decreased to 40 per liter but the mean ice crystal size had
increased to 166 JLm. This appears to be a seeding
signature that warrants closer examination.

'.z '-''"'-....;,

A visual inspection of the 2D-C particle images
during portions of the five monitoring passes is possible in
Figure 5. The vertical lines in each panel are 800 Jim long
and the particles can be scaled by using this line as a
reference. The times (in secs) in the left margin of each
panel are the elapsed tiimes between the passage of the
seeder aircraft and the times that the monitoring aircraft
intercepted the seeding track. If the times are short, the
nucleated particles might be too small to be detected by the
2D-C probe.

Nothing is evident in the images during the first two
passes. Note the two large ice particles during the latter
portion of pass 1 (panel 2). Such particles, although low in
concentration, were comlnon during the MOLAS program.
They had an origin that was independent of the aircraft and
the nucleant releases.

UW KING AIR FLIGHT TRACK

DATE. 891202 TINE INTERVAL. 102200-103800

TO'.,," ....hU... I.. PAOHA IStANO. CA

".

DISlAliC( u.. ...t I

Figure 4 Flight track of the University of Wyoming
King Air during the second test of the P. syringae
nucleant on 2 December 1989.

Table 1.

Pass Data Summary for MOLAS

Date Begin
Time
(PST)

FSSP CON FSSP d
Avg TAS PASS TRF Avg. Max MIN MAX MIN MAX
(m/see) I Oc JW LWC (l/em3) (microns)
(gm/m3)1 (6 sec. avgs.) (6 sec. avgs.)

2D-C
MAX CON d
(#/1) (5 see
(1 see mean
value) size)

Comments

1212 100833 0 drop of 10 gm of Pseudomonas Syringae
from Cessna 421
1212 1009~8 96 1 -8.0 0.25 10 102 11 13 1 5~ no evidence of plume
1212 1011~2 95 2 -7.6 0.20 9 135 11 1~ 1 59 no evidence of plume
12/2 101~36 96 3 -7.8 0.20 27 126 11 12 2 65 no evidence of plume
12/2 101700 100 ~ -7.5 0.20 2 10~ 10 17 2 107 no evidence of plume
1212 102~50 0 drop of 100 gm of Pseudomonas Syringae
12/2 10255~ 87 1 -7.7 0.20 62 109 10 11 2 1~8 no evidence of plume
12/2 1027~8 85 2 -7.6 0.20 19 1~6 11 12 1 60 no evidence of plume
12/2 103012 93 3 -7.6 0.20 2 87 10 17 155 85 obvious penetration of plume
12/2 103248 96 ~ -7.2 0.20 18 125 10 12 9 13~ still :In plume
1212 103606 97 5 -7.5 0.25 7 1~0 10 15 ~O 166 still in plume
file: \bill\tablel.ps
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