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<br />4. CONCLUSIONS
<br />
<br />There is little doubt that the P. syringae particles
<br />nucleated ice crystals in a supercooled fog at _8oe, since the
<br />aircraft were flown at power settings during the nucleation
<br />tests that should have eliminated the generation of Aircraft
<br />Produced Ice Particles (APIPs). To our knowledge this is
<br />the first test of this nucleant in the atmosphere for which
<br />quantitative confirmation o~ its n~c1eating cap~bilities ~as
<br />been possible. The seedmg SIgnature begms as hIgh
<br />concentrations of small particles which grow with time. The
<br />mean, median and modal particle sizes are nearly equal in
<br />the plume, suggesting a common origin for the ice crystals.
<br />The primary initial crystal habit appears to be columns or
<br />needles, which rime during the growth process.
<br />
<br />Our failure to detect a seeding signature for the
<br />release of the 10 gm of nucleant must be interpreted as a
<br />failure to penetrate the plume by the measuring aircraft
<br />due to the limited dispersion and resultant areal extent of
<br />the plume. Passage of the measurement aircraft just a few
<br />meters above or below the track of the seeder aircraft
<br />could account for missing the plume in the light seeding
<br />case.
<br />
<br />Additional atmospheric tests of the P. syringae
<br />nucleant at warmer temperatures are desirable to learn its
<br />true nucleation capabilities in a temperature zone that is
<br />not serviced well by conventional nucleants, such as silver
<br />iodide. These initial quantitative atmospheric tests indicate
<br />that P. syringae may prove to be a valuable tool for
<br />artificial nucleation in the atmosphere.
<br />
<br />5. ACKNOWLEDGEMENTS
<br />
<br />This research was done within the context of a study
<br />of Aircraft-Produced Ice Particles (APIPs) that was funded
<br />by the National Science Foundation under Grant No. A TM-
<br />8813846.
<br />
<br />We are especially grateful to Mr. Glenn Gordon of
<br />the University of Wyoming for processing much of the data
<br />that were used in this article. His knowledge and expertise
<br />were invaluable to the success of our efforts.
<br />
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