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<br />~ . <br /> <br />, . <br /> <br />8.17. Super, Arlin B., . 1995b: Observations of microphysical effects of liquid propane seeding on <br />Utah's Wasatch Plateau during early 1995. Appendix E of Bureau Reclamation Research - <br />Report R-95-12, Bureau of Reclamation, Denver, CO, 109-133. . <br /> <br />INTRODUCTION <br /> <br />A series of limited cloud seeding experiments was conducted from December 13, 1994, through March 11. <br />1995, on the Wasatch Plateau (hereafter Plateau) of central Utah. The primary purpose of the experiments <br />was to investigate the ability of AgI (silver iodide) to create significant ice particle concentrations within <br />orographic (mountain-induced) cloud at slightly supercooled temperatures. However, a secondary <br />purpose was to document microphysical effects of high altitude liquid propane seeding. The evidence <br />obtained from a limited number of liquid propane seeding experiments is the subject of this report. <br /> <br />The experiments were simple in design. Liquid propane was released in I-h "pulses" from a single HAS <br />(High Altitude Site) on the Plateau's windward (west-facing) slope. Microphysical effects of the propane <br />seeding were observed at a fixed downwind site (the Target) on the Plateau's top west edge. Both sites <br />are indicated on Figure E.l. Instruments at the Target permitted verification that propane-seeded cloudy <br />air passed by the Target, and permitted monitoring of ice particle characteristics before, during, and after <br />each passage of seeded air (each pulse). Various instrumentation at both sites provided supporting <br />measurements of wind, air temperature, and the presence of SL W (supercooled liquid water). <br /> <br />(Figure E.l not included here) <br /> <br />SUMMARY AND RECOMMENDATION <br /> <br />The IPC observations during the second experiment of March 11 th, taken together with those from March <br />5th, both argue for improved field documentation of propane effectiveness, especially at temperatures <br />above -5 C wh~reAgI is believed ineffective. It may be that higher propane release rates are appropriate <br />for slightly supercooled temperatures. There is no doubt that propane seeding can increase snowfall at <br />such temperatures when excess SL W is available. The questions yet to be answered are what release rate <br />is required to produce significant snowfall, and is such a release rate economical? The potential <br />importance of being able to seed slightly supercooled cloud, which is found in abundance, especially in <br />California but throughout the intermountain West as well, is too great to ignore these questions. <br /> <br />The approach used in these experiments can provide valuable information to partially address the <br />effectiveness of propane seeding. It is recommended that several additional propane seeding experiments <br />be conducted on the Plateau between the HAS and the Target. These experiments are simple and <br />economical, and targeting of the Target site is routine with southwesterly flow. Future experiments of this <br />type should concentrate on periods with no more than very light natural snowfall. It is usually not <br />possible to detect microphysical changes caused by seeding during higher natural snowfall rates because <br />of the variability of such snowfall. <br /> <br />, . <br /> <br />, . <br /> <br />65 <br /> <br />~- <br />