WMOD00402

• Project Name: Sierra Cooperative Pilot Project
• Title: Sierra Cooperative Pilot Project - Final Report for Period November 1984 - September 1986
• Date: 6/1/1987
• Weather Modification - Doc Type: Report

I
I

2.3

I

2.

Locating Regions of Supercooled Liqui~ Capture by
Snowflakes in Cloud Using the Stable isotopes of Water
and Ice Crystal Structures.

I

I

An estimate of the range of elevations within the cloud system where
the bulk of the precipitating water is being captured, can be obtained by
measuring the 180/160 ratio in the snowfall water. By observing also the
ice crystal habits and degrees of riming or accretional growth we ~in
obtain valuable information on temperatures (and elevations) of cryi;tal
formation.

I

I

The liquid water droplets in the cloud, prior to accretional ~ipture,
will have stable isotopic compositions (180/160 ratios) given by thla equi~
librium ratios corresponding to their ambient temperatures. Once fl!:'ozen
onto the growing or falling ice crystal this resulting frozen element of
the crystal will retain that isotopic ratio provided no evaporation occurs
during its passage to the ground.

I

I

In sununary, the plan for this section. of the research program is to
combine the chemical and isotopic analyses with the ice crystal structures
to obtain better insights into:

I

1.

the extent to which AgI is captured by the snow in
the target area:

I

2.

the use of this data for verification and continuing
development,ofthe GUIDE model used for targeting
prediction:

I

3.

the locations of regions of supercooled liquid water
in the cloud systems of interest: and

I

4.

the extent to which this technology might be used
for covariate analyses of randomized seeding programs
both in the Sierra Nevada and elsewhere.

I

( c) The Field Proqrams:

I
I
I

After beginning of the contract period, all necessary preparations
for the 1984-85 field season were completed. These activities included
installing the portable snow collector (to be used for the time sequential
sampling at the Kinqvale (HALO) site and related equipment in a dedicated
field vehicle. Several discussions were held with Bureau of Reclamation
personnel as to the best location for the sampling activities which was
approximately one-half mile to the east of the Kingvale site. No appro-
priate alternative sites could be located. This is the same locatic)n used

I
I