Types of Cloud Seeding

Hygroscopic Seeding

• Hygroscopic seeding is used in warm cloud masses (above 0 degrees Celsius or 32 degrees Fahrenheit). Large hydroscopic particles (sodium chloride) are sent into a cloud to enhance the formation of "collector drops" that grow into raindrops.

Glaciogenic Seeding

• Static Glaciogenic seeding is used in cold clouds (less than 0 degrees Celsius or 32 degrees Fahrenheit) and is designed to produce precipitation by causing ice particles to grow. It involves adding ice crystals (silver iodide and dry ice) to the clouds that will promote further crystallization and precipitation. Both elements, silver iodide and dry ice, are so cold they cool the surrounding crystals and cause more ice to form.

Aerial Seeding

• Aerial cloud seeding is considered the most effective because of the proximity to the clouds. It delivers the seeding agent using aircraft either from the top or bottom of the cloud. Releasing agents from the top involves direct injection straight into the cloud. Releasing agents from the bottom involves using the updrafts from the cloud.

Ground-Based Seeding

• Ground-based seeding can be a good resource if the cloud cover is extremely low or if the clouds cover varied terrain. Injection of seeding agents from the ground is done using flares and rockets.