Night Versus Day Cloud Seeding in Langmuir's Periodic Experiment

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  • 1 Office of Atmospheric Resources Management, Division of Research, Bureau of Reclamation, U.S. Department of the Interior, Denver, CO 80225
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Abstract

During the last ten 28-day cycles of Langmuir's periodic seeding experiment, beginning 15 October 1950, silver iodide smoke generators were operated one day each week from 1600 to 2400 LT on odd-numbered cycles and from 0800 to 1600 LT on even-numbered cycles, to see if daytime inactivation of the smoke would affect the outcome. However, the differences between nighttime-seeded and daytime-seeded cycles went unanalyzed. Analysis of previously published data now shows that the weekly periodicity of precipitation was greater during nighttime-seeded than during daytime-seeded cycles, especially in the block of analysis regions east-northeastward from the seeding site at Alamogordo, New Mexico. The same was true with respect to periodicity of temperature at the 70 kPa level over Omaha, Nebraska. Between nighttime-seeded and nonperiodic-seeded cycles there was a greater difference than between daytime-seeded and nonperiodic-seeded cycles. Whether these differences were caused by seeding remains unsettled. No accepted theory supports the hypothesis of effect, but if it were true it would be of immense importance.

Abstract

During the last ten 28-day cycles of Langmuir's periodic seeding experiment, beginning 15 October 1950, silver iodide smoke generators were operated one day each week from 1600 to 2400 LT on odd-numbered cycles and from 0800 to 1600 LT on even-numbered cycles, to see if daytime inactivation of the smoke would affect the outcome. However, the differences between nighttime-seeded and daytime-seeded cycles went unanalyzed. Analysis of previously published data now shows that the weekly periodicity of precipitation was greater during nighttime-seeded than during daytime-seeded cycles, especially in the block of analysis regions east-northeastward from the seeding site at Alamogordo, New Mexico. The same was true with respect to periodicity of temperature at the 70 kPa level over Omaha, Nebraska. Between nighttime-seeded and nonperiodic-seeded cycles there was a greater difference than between daytime-seeded and nonperiodic-seeded cycles. Whether these differences were caused by seeding remains unsettled. No accepted theory supports the hypothesis of effect, but if it were true it would be of immense importance.

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