Severe Storms

Unmanned flying vehicles can take a closer look at severe storms to find out what turns relatively minor storms into big ones. Investigating storms with robot aircraft

Rainstorms often become thunderstorms with lightning, hail or even tornadoes. But scientists aren’t sure why one rainstorm remains harmless while another becomes dangerous. Scientists normally study storms by setting up measuring tools on the ground. In that case, they have to wait for a storm to come to them. Some aircraft can fly through storms — but typically they can’t observe a storm for more than a few minutes.

Last storm season — in August of 2012 — scientists at NASA’s Marshall Space Flight Center conducted an experiment using an unmmanned aircraft to study storms in a more sustained way. The craft measured air currents and electrical and magnetic changes in storms over Florida’s Everglades. Scientists remotely controlled the plane and made it fly above the storms for several hours — a feat too dangerous for a piloted plane. Steve Goodman is an atmospheric scientist, who helped predict when and where thunderstorms might emerge — and so where to send the unmanned craft.

Steve Goodman: There has been discussion over the last few years as these unmanned aerial vehicles can have longer and longer operation times to, say, follow a nascent hurricane forming off the west coast of Africa and actually staying on it and following it all the way to the United States when it makes landfall. I guess that’s the dream that the scientists have right now.

The project mentioned in today’s show is called ACES (Altus Cumuls Electrification Study). It was conducted in August and September of 2012. The plane itself is called Altus. It’s essentially a commercial version of the remotely controlled Predator aircraft.

Pilots do fly missions to study severe storms. But they are only able to stay above a storm for a few minutes. And it’s a pretty dangerous thing to do. Doug Mach, head of the ACES experiment’s education effort, clarified, “it is really the combination of boredom/danger/duration that sets the UAV apart, you don’t want a bored, tired pilot in danger.” By contrast, the Altus plane stayed above a series of storms for six hours.

One region where storms often intensify is the boundary between two air masses that are at different temperatures. These boundaries often increase a mild storm’s updrafts.

Updrafts — that is, air currents that flow upward — control the strength of the storm for two reasons. First of all, if an updraft is strong, that means it can support big drops. Clouds with weak updrafts will have misty raindrops — the air currents aren’t strong enough to keep big drops in the air. Secondly, clouds with strong updrafts push raindrops higher into the atmosphere, where it is colder. This enhances the production of ice, which in turn can increase the likelihood of lightning.

Sometimes air boundaries are formed by the leftovers of an older storm. Part of the UAV experiment was to see how these storm leftovers and air boundaries affected the newer storms.

Goodman explained that his main role in the ACES project was to make morning weather briefings to help “vector the storm” — in other words, to identify where and when storms might break out. The flights would often take off around 11 am to be at the everglades around 1:00 pm. He noted that sea breezes moving inland are often a trigger for storms. They turn from cumulus clouds to full thunderstorms making lightning. Goodman said, “We saw maybe a half dozen storms. And flew over some oceanic storms too.”

The main part of the six-week experiment was to demonstrate that you could get a plane to a storm and follow it over time. And by that measure, the experiment was a success. There was also some tantalizing data collected. At one point, the aircraft observed waterspouts being formed. Then, lightning was produced by the waterspouts. Goodman plans to look more closely at this data.

According to Goodman, “This could become a routine tool, you could follow a hurricane over Africa, follow it as it crosses the ocean and follow it across, maybe even drop wind or environmental sounding instruments … these are pipe dreams. … Imagine a UAV that could stay up for a week or more.” He said that you could watch these storms as they evolve and put them into forecast models.

NASA is currently looking at developing more UAVs in the future, especially bigger ones that could carry bigger payloads.

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