Analysis of Recording Raingage Data for the Israeli II Experiment. Part I: Effects of Cloud Seeding on the Components of Daily Rainfall

Abstract

Earlier Published analyses of the second Israeli randomized experiment (1969?75) were restricted to 24-h data; this paper provides more details which are based on continuous time data from recording raingages. The present analyses confirm that when cloud tops were warmer than ?21°C, seeding increased the efficiency of precipitation. In the ?21° to ?11°C window, both amount and duration of rainfall increased by some 50%, but no extra rain events appeared. Extra rain events were apparently initiated by seeding when cloud-top temperatures were warmer (?11°C and above); however, this did not significantly increase the amount of rainfall. No effect of seeding was found when cloud tops were colder than ?21°C. It appears that seeding makes the existing process of rain formation more effective and also inducts precipitation formation in some clouds that would not have precipitated naturally.