WMOD00298

• Title: Quantifying Ice Nucleation by Silver Iodide Aerosols
• Date: 5/1/1990
• State: CO
• Weather Modification - Doc Type: Report

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Calibration of the ice particle counts was made versus "ground truth"

collections onto microscope slides. From numerous calibrations, it was

found that the standard deviation in ice particle counts was about 30%

of the total, independent of temperature or ice crystal habit. The

total ice crystal number settled from the chamber was determined by

multiplying the ice particle count by the ratio of liner bottom surface

area to the sample hole area.

A slight measurement lag in detecting freshly nucleated ice

crystals occurs because crystals must grow and settle to the bottom of

the chamber. "Instantaneous" pulse nucleation tests in the chamber

using liquid CO and dry ice injections into supercooled water clouds
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have shown a nearly Gaussian response, peaking 30 to 75 s after

nucleation, depending on temperature and pressure ( which affect

crystal growth rate and fall velocity). A deconvolution procedure is

used to obtain the true response from the measured ice crystal signal

(Mage and Noghrey, 1972). The finite difference approximation to the

Laplace transform which describes the relation between the

instantaneous rate (s -1) of ice crystal formation (R) and the actual

nucleation response (X) is given by,

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R(t) -

n-T/t:.t
L C(n) X(t - nAt) t:.t

(3.1)

n-l

where the coefficients C(n) represent a transfer function describing

the response to a unit impulse of ice crystals, T is the total time