Case Study: Cloud Seeding

Case Study Cloud Seeding to Increase Rainfall ? The data were collected in southern Florida between 1968 and 1972 to test a hypothesis that massive injection of silver iodide into cumulus clouds can lead to increased rainfall. In this experiment, on each of 52 days that were deemed suitable for cloud seeding, a random mechanism was used to decide whether to seed the target cloud on that day or to leave it unseeded as a control. An airplane flew through the cloud in both cases, since the experimenters and the pilot were themselves unaware of whether on any particular day the seeding mechanism in the plane was loaded or not (that is, they were blind to the treatment). Precipitation was measured as the total rain volume falling from the cloud base following the airplane seeding ran, as measured by radar. Did cloud seeding have an effect on rainfall in this experiment? If so, how much? Number of cases: 26 Variable Names: 1. Unseeded_Clouds: Amount of rainfall from unseeded clouds (in acre-feet) 2. Seeded_Clouds: Amount of rainfall from seeded clouds with silver nitrate (in acre-feet) The Data: Unseeded_Clouds Seeded_Clouds 1202.6 2745.6 830.1 1697.8 372.4 1656.0 345.5 978.0 321.2 703.4 244.3 489.1 163.0 430.0 147.8 334.1 95.0 302.8 87.0 274.7 81.2 274.7 68.5 255.0 47.3 242.5 41.1 200.7 36.6 198.6 29.0 129.6 28.6 119.0 26.3 118.3 26.1 115.3 24.4 92.4 21.7 40.6 17.3 32.7 11.5 31.4 4.9 17.5 4.9 7.7 1.0 4.1