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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. the aggregates, and the delicate way in which the crystals were attached to

each other, they were sometimes not replicated very well by the continuous

particle sampler. Large aggI'egates generally left a circular impression in the

Formvar.

There appeared to be a definite threshold concentration of individual

crystals below which aggregation did not occur. Also, there was an increase in

the concentration of aggregates as the concentration of large ice particles

{greater than about 200 ~m in maximum dimension) increased. The concentration

of aggregates also increased as the temperature increased provided other

atmospheric conditions remained constant. There was also an increase in the

concentration of aggre~ates with a decrease in altitude and with increasing

depth of the cloud. An increase in the concentration of aggre~ates with

increases in air turbulence and with the relative strength of the orographic

effect of the Cascades was also noted. Also noticeable was a decrease in the

concentration of individual particles and aggregates on the east slopes of the

Cascades compared to the west slopes. Often an increase in the concentrations

of ice particles and aggregates was accompanied by a marked decrease in the

concentration of water droplets.
4.4 Riming
Riming of ice particles was observed both in the aircraft and ground

observations. Riming was more common'on crystals which ~ew at temperatures

above -200C. Aircraft observations indicated the following trends. Cold

region crystals such as bullets, columns, and side planes were generally not

rimed. This was attributed to the large ratio of ice particles to water

droplets at these low temperatures. Plates were only occasionally rimed but