WMOD00317

• Contract/Permit #: 14-06-D-6999
• Project Name: CAWRP
• Title: Cascades Atmosphere Water Resources Program - Volume I
• Prepared For: US Department of the Interior Bureau of Reclaimation
• Date: 7/1/1970
• Weather Modification - Doc Type: Report

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Needles were collected from the aircraft flying at low levels over the
Puget Sound Basin. The observations confirmed the conclusion of Magono and
Lee (l966) and Ono (1970) that needles grow in the temperature region between
-4 to -6oC under water-saturated conditions. The needles collected in the air
were generally elementary needles (Nla), but bundles (Nlb) and even a few
combinations of needles (N2a) were observed. The needles ranged in length
from about 350 to over 3000 ~m, with an average length of 850 ~m. The needles
din nut l'eflch a limiting a-axis dimension of 60 urn as noted by Ono (1970).
Needles with widths up to 160 urn were observed. The needles observed in the
Pacific Northwest storms appear to have a smaller length to diameter ratio than
that reported by Auer and Veal (1970).
At ground level in the Cascade Mountains, most of the needles occurred as
parts of aggregates or in combinations. Needles up to 4000 urn long were
collected, but the average length was 1500 urn. There appeared to be more low
level moisture available for the growth of needles over the Cascades. However,
due to the methods of collection t, it was also possible to collect larger
needles at the ground than from the aircraft.
Both the air and ground observations indicate that needles can be broken

up in the air. Most easily broken were fragile knife-edge tips which protruded

from the main body of the crystal.

4.2.2 Sheaths (Nlc, Nld, N2b)

Differentiation between sheaths, warm slender columns, and needles was

often extremely difficult. A more workable definition to differentiate between

these crystals is needed.

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