Some Physical Evidence of AgI and Liquid Propane Seeding Effects on Utah's Wasatch Plateau

Authors

  • Arlin B Super Bureau of Reclamation Denver, CO
  • Edmond W Holroyd, III Bureau of Reclamation Denver, Colorado

Abstract

A series of cloud seeding experiments were conducted on Utah's Wasatch Plateau during the winter of 1994-95.  Their purpose was to permit physical assessment of the effects of both silver iodide and liquid propane seeding, particularly at only slightly supercooled temperatures.  Seeding materials were released in 1-hour pulses from a location well up the plateau's windward slope.  The terrain often channeled the seeding plumes to an observing site, or target, located at a canyon head on the plateau top's upwind edge.  Snow particles were detected at the target with a vane-mounted 2D-C optical array probe whose strobing speed was governed by an anemometer.  AgI nuclei were detected there by an NCAR ice nucleus counter to confirm the prescence and successful targeting of seeding materials.  Seeding with AgI under cold conditions produced obvious large increases in ice particle concentrations and measurable increases in precipitation at the ground during one experiment.  Seeding with AgI under only slightly supercooled conditions, in which the contact-freezing mechanism is not expected to be effective, typically produced a negligible ice particle supplement.  A forced condensation-freezing mechanism may have been operable during two experiments, producing detectable enhancements in the particle concentrations, but further verification is needed.  Liquid propane seeding produced measurable increases in ice particle concentrations in some experiments, showing it to be an alternative to AgI at only slightly supercooled termperatures.

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Scientific Papers