WMOD00514

• Title: Preliminary Field Experiments of Snowmax on Cumulus Mediocris Clouds to Artificially Induce the Production of Ice Particles
• Weather Modification - Doc Type: Report

malfunction with the liquid water probe
made this impossible. A series of clouds
at different temperatures were to be used
to determine the effects of Snomax as an
ice nucleant at temperatures between -20
and -60C. To do this a relatively large
field of cumulus mediocris to cumulus
humilis were necessary.

2.2 Instrumentation

Quantitative measurements of the
number of ice particles and general
atmospheric condi.tions were accomplished
by using a SPEC model III ice particle
counter, Rosemont Temperature Probe, EG+G
system dew point hygrometer and a Loran
position indicator. These values were
acquired and recorded by an airborne data
system using a 2-80 based microprocessor.
This system was designed to record data at
one second intervals and be written to
floppy disks.
The ice particle counter (IPC) is a
cross pOlarized ice particle counter which
uses the concept reported by Turner and
Radke (1973) and is explained by Lawson
and Stewart (1983). The measurements with
the higher particle counts were smoothed
by using a 5 second average for that point
similar to Lawson and Stewart (1983).
The Rosemont temperature probe uses a
platinum resistance temperature element
and has a range of +500 to -SOoC with an
accuracy of O.SoC and a resolution of
O.loC. Comparison of this instrument with
others during the North Dakota Thunder-
storm Project (Boe et al.,1989) showed a
consistent error of 1.00C colder than the
actual temperature. For the purpose of
this paper the graphs have been adjusted
to show the actual temperature (lOC has
been added to the measured temperature) .
. The aircraft used was a Beechcraft
Duke which has beensui.tably modified to
accommodate the instruments for weather
modification experiments.

3. RESULTS

A total of five different clouds were
seeded with SnOmax. The first two candi-
dates were within a series of clouds which
were approximately 3 to 4 km apart. Analy-
sis of the flight track shows that after
seeding the initial flight. path was not
intercepted. Consequently there were no
measurements made of the seeded areas.
The third candidate was seeded at
temperatures between -1.50 and -2.SoC of
which there were no ice particles detected
before seeding. Subsequent penetrations
were conducted at 3 and 5 minutes after
seeding. Little or no airframe icing
occurred during any of the penetrations.
There were also no signs of growth by the
cloud during the duration of the experi-
ment. Ice particles were not expected at
this temperature because according to Fig.
1 the activation temperature of Snomax was
not reached.
After Climbing back to the -SoC level
a fourth candidate was chosen for seeding.
On subsequent passes at 3, 6 and 11

,.;.

.,
'-

minutes after seeding no significant
amounts of ice partiCles were detected.
Airframe icing occurred on each of the 3
penetrations. This cloud grew and event-
ually formed an a,nv il. Determina tion of
ice crystal concentrations at cloder temp-
eratures higher in the cloud was not
attempted.
The fifth candidate was similar to the
fourth, and was seeded on the first two
passes through the cloud with a total of
30g of Snomax. On the first pass through
the cloud there were very few ice
partiCles detected (Fig 2a). Cloud temp-
erature was somewhat variable, and the
ride was moderat.O!ly turbulent (f ig. 2b).
The second pass, 3 minutes later, was
smoother with a more consistent updraft.
There were more ice particles detected,
but still not in high concentrations, and
with a more uniform cloud temperature
(Fig. 3). During both the first and
second passes the aircraft accumulated as
much as 7 mm of ice on each pass.

c: 2000
0
~ 1600
C
'"
0
c: ~ 1200
0'"
u:::
...J
"'-- 800
~#
;;;
a. 400
'"
~
0
0

--.--.--1

r-

,- I
10 15

,
35

40

20

25 30

5

Time In Cloud
Sec
-2 -------- on__._._______

-3
'"
:;
~ -4
~u
~o -5
E
~
-6

-7

-8

I
10

25

IS

.10

.I~

.:r

20

o

Time in Cloud
Sec

F.iguJte 2. al I c.e paJLtic.le c.ollc.ent.w..t.<.on
and b I ctoud tempelUU:uJte 06 .{Ju"uaI. Hed-
ing penet~on.

There were some definite changes in
the cloud by the time of the third pass (7
minutes after initial seeding). The cloud
had grown approximately 2000 ft in height
since seeding. Upon entering the cloud
the ride became turbulent with varying
degrees of updraft and downdraft
intensity. Significant numbers of ice
particles were detected along with warmer
temperatures as shown in Fig. 4. During
this pass the aircraft accumulated only
small amounts of airframe ice. These

154