WMOD00315 ‎(2)‎

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

S L W Flux Precipitated

Over a 10-km Distance

January-March, 1985
423 hours with SL W ~ 0.01 mm
275 mm precipitation were recorded
127 mm additional precip possible

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Figure 2-7. - Flux of SLW distributed evenly over a l()'km distance downwind of radiometer. Calculations
were based on Integrated SLW measured by microwave radiometer, and winds recorded 70 m a.g,1. above
the Mesa during January through March, 1985. The 127 mm of precipitation calculated was 46 percent of
the 275 mm that was actually recorded by a nearby high-resolution gauge.

a single 5-hour period in late March during which an SLW
between 0.80 and 0.90 mm was recorded, which accounted
for 15 percent of total flux.

2.5.2 Distribution of SLW Episodes. - An episode of SLW
was defined as the continuous presence of SL W as mel\sured
by the radiometer, and uninterrupted for longer than 2 hours.
If SL W was again detected within 2 hours, the episode was
considered to be continuous. Using this somewhat arbitrary
definition, many hours usually passed prior to the onset of
another episode. Periods of missing data were ignored. Hours
of valid data immediately preceding or following missing data
were not evaluated due to episode length ambiguity.

The cumulative distribution of the 115 SLW episodes re-
corded during the 5-month period is shown by the solid line
on figure 2-8. Fifty percent of the episodes were less than
3 hours in duration, while only 12 percent were 12 hours
or longer. The longest episode was 41 hours.

Considering the number of hours contained in the episodes
of any given duration and not the number of episodes, the
perspective changes considerably. For example, figure 2-8
shows that 50 percent of all SLW episodes were less than

3 hours; however, the number of hours contained within
episodes of 3 hours and less was only 14 percent of the total
hours of SLW. Thus, cumulative distribution of hours of SLW
shows that 50 percent of all hours of SL W were contained
in episodes that were 15.7 hours and longer, as shown by
the dashed line on figure 2-8.

The SL W episodes longer than 5 hours comprised 80 percent
of the total hours, so the time available for an effective seed-
ing response was often greater than originally thought. A
2-hour time lapse from detection of SLW to onset of effective
nucleation (by seeding) would result in 210 hours (24 percent)
being "missed". The impact in terms of missed flux might
be considerably less because the greater SLW amounts in
any given episode frequently did not OCCllr at the episode
onset, but rather some hours later.

2.5.3 Rosemount Icing Rate Meter. - Wind tunnel calibrations
showed that the Rosemount icing rate meter would "trip"
at an average loading of 0.09 g. Approximate values of LWC
were calculated from the number of trips in 1 hour using the
equation:

LWC = NM
cAs

(1)

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