WMOD00315 ‎(2)‎

• Title: Colorado River Augmentation Demonstration Program - Technical Report January 1983 - March 1985
• Date: 4/1/1986
• Weather Modification - Doc Type: Report

2.5 Temporal Distribution of
SLW

Radiometer data were recorded as 2-minute averages, which
were later averaged to the nearest 0.01 mm for I-hour in-
tervals for November and December 1983, and January
through March of 1985. Periodic tipping curves were con-
structed to maintain proper calibrations. The radiometers
were always operated in a vertically-pointing mode. In the
absence of liquid water, the liquid values recorded were
slightly negative or zero. Thus, any positive I-hour average
represented the actual presence of liquid water.

Over the 5 months, valid data were recorded for 3351 hours,
or 92 percent of all possible hours, of which 958 hours (29
percent) had average liquid water amounts of 0.01 mm or
more. Surface temperatures recorded at the GMO (elevation
3290 m) during periods of liquid water were less than 0 oC
98 percent of the time; therefore, the liquid water recorded
by the radiometers can be considered supercooled.

2.5.1 Distribution of SLW Amounts. - The distribution of
the SLW amounts discussed in section 2.5 is shown on figure
2-6. The median value is 0.08 mm. Only 5 percent of the
958 hours were greater than 0.50 mm, while 57 percent

60

indicated 0.10 mm or less. The greatest hourly average was
1.07 mm [13].

To put these amounts into perspective, consider a hypo-
thetical environment that is shear-free, with the wind speed
from the .surface upward being constant and equal to that
measured by the sensor 70 m a.g.1. at the GMO. The SLW
flux from the radiometer to cloud top and perpendicular to
the wind would then be the integrated SLW multiplied by
the wind speed. Assuming that all the SLW flux might be
precipitated uniformly within a lO-km distance, approxi-
mately the cross-axis width of the Mesa, an upper limit on
seeding potential can be estimated.

'tl-I

For the January through March 1985 period, during which
the 70-m wind sensor was in operation, 423 hours with an
average SLW greater than or equal to 0.01 mm were re-
corded. As measured by a high-resolution precipitation gauge
near the radiometer, 275 mm of precipitation actually fell
during these 3 months. The maximum additional precipita-
tion that might be obtained by complete precipitation of the
SLW flux within 10 km is 127 mm (fig. 2-7). This amounts
to an additional 46 percent, most of which would be derived
when SLW amounts of 0.30 mm or less were recorded by
the radiometer. The higher SLW amounts did not generally
contribute significantly to the total flux. The exception was

~ 50
en
:I:
t:
~ 40
en
a:
:;:)
0
:I: 30
LL
0
W
"
<(
~
Z
w
()
a:
w
l:L.
>,1
0
0.0 0.2 1.2

Figure 2-6. - Distribution of I-hour averages of SLW recorded by microwave radiometer for 958 hours during
November and December 1983. and January, February, and March 1985.

10