WMOD00508

• Title: Physical Response of Winter Orographic Clouds over the Sierra Nevada to Airborne Seeding Using Dry Ice or Silver Iodide
• Date: 4/4/1990
• Weather Modification - Doc Type: Report

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DESHLER, REYNOLDS AND HUGGINS

291

APRIL 1990

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of the seedline selected by the OTM, or the radiometer
measured SL W > 0.1 mm for the previous 10 min.
After seeding began the cloud physics aircraft mea-
sured the initial growth of seeded ice crystals by tracking
a parcel of air as it drifted downwind from the seedline.
By integrating true airspeed and heading, the computer
on the research aircraft could direct the pilot to make
repeated penetrations of a point drifting with the wind
(Cooper and Lawson 1984; Huggins and Rodi 1985).
An attempt was made to track a point on the seedline
where the SL W was initially >0.05 g m -3. The 5-cm
radar at SHR performed continuous surveillance of
the seeded region. Intensive surface observations began

at KGV when an experimental unit was declared, and
continued for an hour beyond the time when seeding
effects were expected to have passed. Since KGV was
typically 45-60 min downwind of the seedline, the ob-
servations there bracketed expected seeding effects by
an hour or more.

e. Seeding material

Because of the warm temperatures, > -1OoC, at
which seeding opportunities were found to exist, the
primary seeding material used was CO2. The dry ice
was dispensed at a rate of 0.2 to 2 kg km -1 from a