WMOD00311 ‎(2)‎

• Title: Climatologies and Intercomparisons of Rawinsonde Data Collected During Winter Storm Periods in Utah
• Date: 8/1/1980
• State: UT
• Weather Modification - Doc Type: Report

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a mixing ratio of 3 gKg-1 at cloud base has been used as a
lower limi t .

For item three, bounds of cloud top temperature between
-10 anq -30oC were suggested for conditions with insufficient
natural freezing nuclei available to start the precipitation
process. Cloud top temperature is chosen as an index of the
. naturally occurring materials in the atmosphere which will
serve as freezing nuclei. It is known tha.t the acti vi ty of
such materials increase as temperatures decrease.

The bounds for item four were derived from consideration
of the barrier's configuration, cloud depth, wind speed and
direction, and the velocity at which the precipitation particles
fall. Under conditions with high cloud tops and strong wind
speeds normal to the barrier, the precipitation particles
could be blown over the crest and evaporate in lee-side downdrafts
causing a decrease in precipitation across the barrier.

Recently, evidence has been presented which indicates
tha t some of the limits suggested by the Vardiman and Moore
study might be subject to question. Accord.ing to Hill (1980)
the atmospheric sampling equipment which was used in the research
programs,prior to 1973 produced errors in humidity measurements
during daytime rawinsonde data collection due to a lack of
adequa te shielding from solar radiation. Hill contends. that
these errors caused much of the daytime sound:Lng data to indicate
warmer cloud tops than actually occurred and could have biased
the apparent reults. Hill's concerns appear justified and
it would seem that additional analysis of the data used in
Vardiman and Moore's study, perhaps using only nighttime sounding
data, would be in order to resolve the question. The concepts
presented by Vardiman and Moore are, however, not in question.
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