|
<br />observations are consistent with the 200
<br />seconds required for the dry bacteria to
<br />grow to a 15-20 urn diameter hydrometeor
<br />found by Levin et al., (1987) and tne 3 to
<br />5 minutes required for 90% nucleation
<br />found by Ward and DeMott (1988).
<br />During the fourth pass through the
<br />cloud (12 minutes after initial seeding)
<br />there were no major changes except there
<br />was a greater conce~tration of ice
<br />particles shortly before exiting the cloud
<br />(Fig. 5). Airframe icing was again
<br />minimal. At this time the cloud had
<br />started to show signs of forming an anvil
<br />and had grown approximately 6000 ft above
<br />its original seeding height.
<br />The final pass through this cloud was
<br />17 minutes after the initial seeding pass.
<br />At this time graupel and raindrops were
<br />hitting the windshield along with high
<br />concentrations of ice particles (Fig. 6).
<br />This cloud had now grown into a small
<br />cumulonimbus with an anvil. Subsequent
<br />passes through this cloud were not at-
<br />tempted due to its size and nature.
<br />The field of cumulus around these two
<br />seeded clouds was still relatively the
<br />same as when we started. The two seeded
<br />clouds eventually ingested same of the
<br />neighboring smaller clouds. Two other
<br />cumulus clouds near the seeded clouds were
<br />penetrated at the -50C level, looking for
<br />natural ice with only small amounts found
<br />(similar to Fig. 2a and 3a). These
<br />"control" clouds were monitored for
<br />approximately 10 minutes without signs of
<br />growth or natural ice production.
<br />Upon descent past cloud base the
<br />fourth and fifth seeded clouds were pro-
<br />ducing rain to the ground with occasional
<br />cloud to ground lightning strokes.
<br />
<br />4. CONCLUSION AND COMMENTS
<br />
<br />Snomax is a bacterial protein which
<br />has an ice nucleating activation temper-
<br />ature between -20 and -50C. While incon-
<br />clusive, seeding at temperatures near
<br />-20C did not produce any detectable ice
<br />crystals while ice particles were detected
<br />in concentrations of 100 liter-I 8 minutes
<br />after seeding at temperatures near -50C.
<br />It is not clear why ice particles were not
<br />detected in the fourth cloud but it is
<br />speculated that penetrations at higher
<br />altitudes and colder temperatures would
<br />have revealed at least some traces of ice
<br />particles.
<br />Snomax shows a potential for use in
<br />rain enhancement type weather modifica-
<br />tion operations on cumulus clouds, al-
<br />though further research needs to be con-
<br />ducted regarding its feasibility for the
<br />use in hail suppression operations. The
<br />major concern here is the two orders of
<br />magnitude less ice particles possible per
<br />gram of Snomax as compared to AgI-AgCl-
<br />NaCl aerosols at temperatures colder than
<br />-120C (see Fig. 1). Snomax being active at
<br />warmer temperatures may prove to be of
<br />greater importance, than total number of
<br />particles produced. Further studies
<br />should be conducted' to determine the
<br />importance of both factors.
<br />
<br />...
<br />
<br />"\..
<br />
<br />\
<br />
<br />5 . ACKNOWLEDGMENTS
<br />
<br />This research has been sponsored by
<br />the North Dakota Atmospheric Resource
<br />Board, the NOAA Federal-State Cooperative
<br />Program in Al:mospheric Modification
<br />Research, Snomax ~~echnologies and Weather
<br />Modification, Inc.
<br />A special thanks to Patrick Ward of
<br />Eastman Kodak Company and Patrick Sweeney
<br />of Weather Modif ication, Inc. for their
<br />help and comments.
<br />Regulatory approval for
<br />activities was provided by the
<br />Dakota Department of Health and the
<br />Dakota Atmospheric Resource Board.
<br />
<br />these
<br />North
<br />North
<br />
<br />6. REFERENCES
<br />
<br />Boe, B. A., P. L. Smith, H. D. Orville, N.
<br />C. Knight, M. Hjelmfelt, D. A.
<br />Griffith, J. L. Stith, AND R. F.
<br />Reinking, 1989: North Dakota
<br />Thunderstorm Project Field Operations
<br />Plan, May 1989. 75P.
<br />
<br />Gregory, P. H., 1967: Atmospheric micro-
<br />bial cloud systems. Sci. Progr.
<br />Oxford, 55, 613-628.
<br />
<br />Lawson, R. Po, and R. A. Stewart, 1983: An
<br />improved optical ice particle
<br />counter. Preprint 5th Symposium on
<br />Meteorological Observations and
<br />Information,. Am. Meteor. Soc., 46-53
<br />
<br />Levin, Z. and S.A. Yankofsky, 1988: Ice
<br />nuclei of biOlogical origin. In
<br />Lecture Notes in Physics: Atmospheric
<br />Aerosols and Nucleation, P. Wagner
<br />and Vali (eds.), Proc. of 12th Inter-
<br />national Conf. on Atmos. Aerosols and
<br />Nucleation, 645-647.
<br />
<br />, Z., S. A. Yankofsky, D. Pardes and
<br />N. Magal 1987: Possible application
<br />of bacterial condensation freezing to
<br />artificial rainfall enhancement. J.
<br />Clim. Appl. Meteor., 26, 1188-1197.
<br />
<br />Arny and C. D. Upper,
<br />herbicola: a bacterial
<br />active in increasing
<br />to corn. Phytopathol.,
<br />
<br />Lindow, S. E.,D. C.
<br />1978: Ereinia
<br />ice nucleus
<br />frost injury
<br />68;' 523-527.
<br />
<br />,S. S. Hirano, W. R. Brachet, D. C.
<br />Arny and C. D. Upper, 1982:
<br />Relationship between ice nucleation
<br />frequency of bacteria and frost
<br />injury. Plant Physiol., 70, 1090-
<br />1093.
<br />
<br />Mandrioli, P.. G. K. Puppi, N. Bagni and
<br />F. prodL 1973: Distribution of
<br />micro-organisms in hailstones.
<br />Nature, ~~, 416-417.
<br />
<br />Maki, L. R. and K. J. Willoughby, 1978:
<br />Bacteria as Biogenic Sources of
<br />Freezing Nuclei. J. App1. Meteor.,
<br />12., 1049-1053.
<br />
<br />156
<br />
|