Researchers have used a variety of aircraft and technologies to perform cloud seeding operations in the 78 years since scientists first began developing it. Cloud seeding is an approach to modify weather, most often for increasing precipitation. The usefulness and safety of this technology has mixed reviews with people and organizations both in favor of it and against it.
Bombers for cloud seeding instead of combat
One of the first uses of cloud seeding occurred on 13 October 1947 when two Air Force B-17s and a B-26 flew into a hurricane 415 miles east of Jacksonville, Florida. Their mission, “Project Cirrus,” was to deploy dry ice into the storm. The purpose was to see if the dry ice would affect the storm’s clouds and precipitation and cause it to change its path.
The first bomber flew at cloud level above the hurricane and dropped crushed dry ice from its belly. The second B-17 followed a half mile behind to monitor cloud changes, and the B-26 trailed behind, directing the first two. The first B-17 made a half-hour run over 100 miles and dumped 80 pounds of the dry ice. The idea was for the dry ice to make drops of water vapor and ice crystals in clouds stick together, forming large, heavy droplets that would fall as rain or snow. The B-17 made two more passes, dropping another 100 pounds of dry ice.
They circled back and noticed the cloud deck below beginning to break up and the cloud top starting to grow larger. This convinced the crews and scientists that the seeding had an effect, but it did not turn out the way they expected. The next day, the storm made a sudden 135 degree turn to the west and strengthened. It struck Savannah, Georgia on 15 October, killing one and causing $2 million, or about $28 million in today’s dollars, in damage in Georgia and South Carolina.
First arguments appear against cloud seeding
This caused a public outcry that the experiment had caused the storm to turn, and people threatened lawsuits. Eventually, scientists proved that other storms had made similar turns without human influence, and the lawsuits did not move forward.
In the years since 1947, researchers have continued developing cloud seeding methods to be able to increase precipitation. Today they are performing cloud seeding operations with more modern platforms including fixed wing aircraft, turboprop aircraft, helicopters, and drones.
Modern aircraft used for cloud seeding
The Beechcraft King Air C90/200 is one such design. Weather Modification International (WMI) in Fargo, North Dakota has installed cloud-seeding equipment on over 100 aircraft including 5 Beechcraft King Air 350s in the past 24 months. These modifications include installing weather research, atmospheric measurement, and cloud-seeding equipment such as ejectable flare racks, burn in-place flare racks, and firing-control boxes. Some of the other aircraft WMI has modified for cloud seeding and atmospheric research include the Hawker 400, Piper Seneca II, and Cessna 340A.
Aircraft deploy flares into clouds to spread particles
The aircraft deploy pyrotechnic flares to scatter cloud seeding agents or particles into clouds. The flares burn as they drop through clouds, releasing particles that promote ice crystal formation. Along with dry ice, silver iodide is also often used for cloud seeding. Its structure is similar to ice crystals, and it can cause water vapor to freeze and grow and then fall as precipitation.
A newer technology for cloud seeding is an electric charge producing device. It uses an electrode to create a strong electric field around the device to release ions from air molecules. These ions attach to water droplets in clouds, making larger droplets
“Charge can influence how a droplet population evolves into larger drops, sometimes reaching raindrop sizes,” said author Giles Harrison.
Obstacles and arguments against cloud seeding
Despite the research and advancement in cloud-seeding operations, it faces some obstacles. Some scientists claim it is not really effective in producing precipitation or cost effective. There is also some debate on whether the silver iodide could be harmful to the environment.
Worldwide interest remains strong
These questions do not seem to be impacting interest in cloud seeding. Currently, more than 50 countries around the world are experimenting with and using the technology. These include China, India, Dubai, Russia, Australia, and South Africa.
Another view of equipment mounted on aircraft for cloud seeding. | Image: Fargojet.com
Credit: avgeekery.com
