The pilots who make it rain

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Source: BBC

By Tao Tao Holmes

When a cloud-seeding pilot flies inside a storm, it is not a matter of flying from point A to point B: you are trying to get something out of the weather all around you. Where do you want to fly, and what are you going to find once you get there?

When you duck inside a cloud, at first, you see almost nothing. Then suddenly, there’s a dark mass coiffed in white, and you’ve got to go right into that dark place. It’s equal parts beautiful and strange.

Cloud seeding, the practice of injecting certain materials into storm cells to enhance precipitation, has drawn interest from a growing number of water-strapped countries – particularly in the past five years. Currently, around 60 countries on five continents are operating cloud seeding operations to enhance rainfall, mainly for reservoirs, watershed, and agriculture.

But figuring out how and when to fly into the clouds is no simple matter.

Pilots are normally not taught to fly in so close to, or straight into, storm clouds. What’s key is teaching people how to keep track of the big picture, monitoring things like wind shear, gust fronts, updrafts, and downdrafts – all the dangerous things you’re taught to avoid when you fly, says Hans Ahlness, vice president of operations at Weather Modification Inc (WMI). To do that properly, a veteran needs to throw a rookie in a plane and show him or her how to navigate at least a couple of storms.

“You don’t learn this stuff anywhere else,” says Ahlness, whose company was founded in 1961after large-scale crop loss due to hail in North Dakota. WMI has since done seeding projects in countries such as Senegal, Mali, Saudi Arabia, Malaysia, and Australia. They get a lot of phone calls and emails when things are dry – whether from Texas, China, or the Middle East – with people asking them to “fix” their clouds.

Timing and an understanding of the life cycle of the storm’s cell are critical to seeding flights

Initial research in weather modification began in the late 1940s, mainly in the US; by the 1960s and 1970s, thanks to major funding from General Electric, cloud seeding gathered pace. But the following two decades saw a gradual lapse in interest and investment, a loss of confidence spurred by unrealistic claims. At least in the US; in places like South Africa, Australia, and Israel, the research continued.

However, only recently have efforts really started picking up again, says Deon Terblanche, who oversees the various climate and weather programmes at the World Meteorological Organization (WMO).

Hygroscopic cloud seeding, which was developed in South Africa in the early 1990s, involves dispersing water-absorbing salts (a mixture of sodium, magnesium, and potassium chlorides) into parts of clouds; the salts then collect water vapour and grow bigger and faster in size before falling as rain. Earlier seeding efforts used silver iodide, whose molecular structure is very similar to ice, but in the 1990s, a shift was made to the non-polluting hygroscopic salts. Under some conditions, ground-based seeding (which may employ anti-aircraft guns or rocket launchers) is cheaper and more optimal; but once you get up to or above the connective clouds, airplanes become necessary.

(Credit: Getty Images)

The method was developed to try and break a drought in the US state of North Dakota (Credit: Getty Images)

By 1999, 40 countries had become involved in cloud seeding efforts, and randomised, double-blind experiments were starting to prove that cloud seeding did in fact work. Currently, estimates for how much seeding increases the amount of rainfall range between 15 and 40%.

A seeding aircraft is normally a regular twin-engine aircraft with racks mounted on the belly and wings, similar to one which launch flares. As a kid, Hans Ahlness would watch these planes take off into the sky every time there was a thunderstorm.

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