WMOD00400

• Contract/Permit #: 14-06-D-6801
• Title: Structure and Seedability of San Juan Storms
• Date: 11/1/1976
• Weather Modification - Doc Type: Report

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38

the most likely candidate, but contact nucleation by particles smaller than

0.02 11m could also account for the observed behavior. Both these nucleation

processes are only poorly measured at present.

3. Ice nucleus measurements

a. Langer filter samples

The filter samples obtained Hith the rotating fiIter sampler (loaned to

us by Dr. C. Langer) shm\red variations both from storm to stOTIn and on differ-

ent parts of the filters. Dr. Langer processed the filters \'lith a "puff"

technique, \\Thich causes Hater to condense on the filter and \vhich generally

yields higher concentrations than obtained in conventional filter processors

operating near or below Hater saturation. Typical concentrations measured in

unseeded situations Here about O.l/liter at -19C, or about five times the

concentration obtained from blank filters. Increases to about l/liter Here

observed in cases Hhere He believed the storms to be seeded; the maximum

concentration observed Has 3/liter at -19C.

Before looking at the results, \ve tried to predict on physical grounds

Hhich cases Hould have seeding material present. Our prediction regarding

seeding took into account the follo\\Ting factors:

(1) It Has calculated from the NCAR Q/A turbulence data that during the

stable stages the AgI Hould not diffuse to the altitudes flown by the air-

craft. The NCAR acoustical ice nucleus counter onboard the NCAR Q/A agreed

Hith these diffusion calculations.

(2) Storm periods where the low-level sounding indicated neutral or

unstable conditions were assumed to be seeded if the seeding generators

Here operated within six hours prior to our flight time.

(3) If the seeding generators were not operating, but blocking flow

conditions had existed continuously from some time when they did operate