WMOD00500

• Title: Observations of Silver Iodide Plumes over the Grand Mesa of Colorado
• Date: 10/10/1988
• State: CO
• Weather Modification - Doc Type: Report

OCTOBER 1988

HOLROYD, McPARTLAND AND SUPER

I
,.

x
all in
ice
U; plume
E :+
~
E .
~ \
.
w .
Q ~+
::;)
!::
~ crest
c x
3
x
10 100 1000
Total ice nuclei per pass

FIG, 5, The average vertical distribution of total ice nuclei counted
for each pass near the crest.

~

ticle plumes were averaged over the same partitions as
in Table 2. The results are not presented because the
various regions of the table were dominated by the data
of particular dates. All the data from the seeding site
were from 2 to 16 km (rather than 14 km as above).
They were combined into the "ice" column in Table
3 and plotted in Fig. 6 to represent a vertical profile of
ice particle concentrations. The concentrations were
generally greater at the higher altitudes, probably as a
result of both the greater effectiveness of the nuclei at
colder temperatures and the decreasing concentrations
at lower altitudes as the ice particles settled and evap-
orated. The bottom of the profile was dominated by
the experiments of 20 March, in which the effects of
evaporation on snow showers were visible in the pho-
tographs of the clouds as well as in the ice particle
measurements.
The regression line [Eq. (1)] fitting the right column
of Table 2 and plotted in Fig. 5 was used to estimate
IN concentrations for comparison with the ice particle
concentrations in Fig. 6. The total IN per pass, C, as
measured at - 20oC, was assumed to be sampled within
a 150 wedge over a crest approximately 7 km down-
wind of the seeding site. The aircraft would pass per-
pendicularly through the plume there at about 95 m
s -I in a time, t, of almost 20 s. The air was sampled
at a rate, r, of 10 L min -I , giving a sample volume of
rt. The counter operated with a loss ofIN to the walls
assumed to be a factor of 10 (Langer 1973). The es-
timated IN concentrations, N, are given by N = IOC j
rt and are listed in the - 200C column of Table 3 for
each 0.2 km layer.
Garvey (1975) gives data on the AgI effectiveness,
E, at various temperatures, T. The concentration of

1139

* Than typical temp,

nuclei effective at other temperatures is N. E( T)j E
(-200C). Several winter months of microwave radi-
ometer and surface temperature measurements have
revealed a typical crest temperature of about -70C
during liquid water episodes (Boe and Super 1986).
An approximate moist adiabatic temperature profile
for these typical conditions is listed in the far right
column of Table 3. The values ofN were converted to
the typical temperature profile and to profiles 30C
warmer and colder for the remaining columns of Table
3. This presumes that the NCAR acoustical counter
observations are similar to AgI activation in natural

u;
E
E
~

I',
-'b'( 1 ,
'ft.'(~'" ~
a\ '3o~ \',
--... / \
-- /
II of\.'~. \"'_./ \
.S aG'\.\ -- 1
--
+ 1
".'"
o\~.~ ".
rest a\ '3 o~ <1- -
--
--
-

W
Q
::;)
~
~
c(

3

10 100
Ice nucleus and particle
concentration L-1

FIG, 6. The vertical distributions of average ice particle concen-
trations resulting from ground-released AgI smoke, and the distri-
butions of ice nucleus concentrations effective at three typical tem-
perature profiles,