Essays --

Cloud seeding is a branch of geoengineering and weather modification that deals with the precipitation that occurs from clouds. Practitioners of cloud seeding techniques attempt to directly affect the levels of precipitation that will occur from a cloud in hopes to either cause more precipitation or alter the behavior and effects of clouds and storm systems. Cloud seeding works by lacing clouds with particles that promote condensation of water molecules. Precipitation will only occur if water molecules become large enough to escape the force of updraft building the cloud. The water molecules condense around solid and liquid particles known as nuclei. (1-WSText7CldF) which are abundant in the atmosphere. Nuclei are grouped into two categories, cloud condensation nuclei (CCN) and ice forming nuclei (IN). CCNs will cause water vapor condensation both above and below the freezing point of water, while INs only create ice crystals at temperatures below the freezing point. (1-WSText) Clouds with temperatures above the freezing point of water, known as warm clouds, form precipitation through the collision-coalescence process (2-WSText7Precip) Droplets of water collide with each other and coalesce to form larger droplets of water which in turn collide with other water droplets. Once they get large enough, the water droplets become rain. Clouds that have temperatures below the freezing point are considered cold clouds and produce precipitation through the Bergeron-Findeisen process (2-WSText7Precip). The Bergeron-Findeisen process says that ice crystals form at the expense of supercooled water. Ice crystals grow because the supercooled water vapor are attracted to the crystals. The Ice crystals have a lower saturation vapor pressure tha... ...ium chloride. The salts attract water vapor and droplets to coalesce and collide, forming larger particles that eventually become precipitation. Instead of spraying the nucleating agent into the cloud like with the static seeding method, researchers fire off flares with salts in them. This method is used to seed clouds in South Africa and Mexico, both of which have shown positive results. Analyzed results of experiments in South Africa shown that hygroscopic seeded clouds developed larger rain masses than those that were not seeded and they kept the total level of rain for longer than non seeded clouds (4-WMODCol). Researchers from the National Center for Atmospheric Research claimed there to be a significant enhancment in precipitation over a 3 year experiemnt in Northern Mexico ((6-WSText7RainM) The final method of cloud seeding is the dynamic method of seeding.