WMOD00298

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

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growth and sedimentation in the experiments where the transfer

function was defined. At this time, observations of the crystal sizes

or habits in the cloud chamber are not available, although a microscope

video camera will be installed to provide this information in the
future.

The transfer function has not been determined exactly ,for the

types of crystals and conditions existing at all temperatures. Clearly,

the form of the transfer function will depend on temperature, pressure,

and saturation ratio, since these all affect ice crystal growth and

sedimentation rates. An estimate of the errors involved by using the

single transfer function (Figure 3.4) at all temperatures employed in

this study can be made by comparing the transfer function to fallout

data obtained from 0 to -20oC in dry ice seeding tests in the

isothermal cloud chamber (Morrison, 1989). The cloud chambers are

similar in size. The only differences involve the crystal growth rate

dependence on vapor diffusivity (which varies with pressure) and fall

speed dependence on pressure. These should be minor influences. It is

also presumed that the dry ice experiments were not overseeded. The

cumulative ice crystal signals at various isothermal temperatures in

Morrison's experiments are presented for comparison to the cumulative

form of the function used to deconvolute dynamic chamber experimental

data in Figure 3.5. The transfer function well characterizes the

average ice crystal appearance rate for the temperature range of

experiments performed in this study (-5 to -200C). In this range,

Figure 3.5 shows that the median time for detection of an instantaneous

ice crystal nucleation signal may be overestimated or underestimated by

a maximum of up to 15s, depending on temperature. The same effect goes