Hurricane intensity forecasts are about to get a lot better.
A new fleet of eight mini weather satellites, collectively called CYGNSS—Cyclone Global Navigation Satellite System—is due to be launched into orbit on Wednesday from a Pegasus XL rocket dropped by an airplane off the coast of Florida. (Update: the launch took place on Thursday morning, and the CYGNSS satellites have successfully deployed.) Each satellite carries an ingeniously simple instrument that will allow scientists to see inside storms and make more accurate predictions about whether a storm will grow or fizzle.
Because a hurricane’s trajectory is determined by large-scale, obvious weather trends, plotting a storm’s path is relatively easy. But over the last 25 years, according to CYGNSS principal investigator Chris Ruf, very little progress has been made in forecasting how and when a hurricane will intensify.
“What makes a hurricane change its intensity is stuff that’s happening right in the middle, in the inner core of the hurricane,” says Ruf. “To predict it, you need to be able to measure it.”
The measurement in question is surface wind speed. Because evaporation at the ocean surface is the engine that feeds latent heat energy into a storm, and the evaporation rate is driven by the storm’s own winds blowing over the water, current wind speed is the best indicator of how much energy a storm will have later.
Until now, scientists have been blinded to what’s happening inside a hurricane by one big limitation—the weather satellites that traditionally measure wind speed don’t have the capability to see through rain (the signals they use have a wavelength similar to the width of the average raindrop, causing the signals to scatter every time they hit one). And the center of a hurricane is, of course, rainy. Current satellites also sample a given spot only every three days, and some storms live their whole lives in that span.
To get around this problem, scientists rely heavily on P3 Orion research aircraft that fly directly into hurricanes, but such flights provide data for only a tiny portion of any given storm, and many storms in their early stages are too far away to be reached with any frequency by aircraft. The result is a wide margin of error in predictions of how a storm will intensify—they can be off by as many as two intensity categories (there are only five).
Take Hurricane Matthew, which recently devastated southwestern Haiti. Just before the storm made landfall, it intensified from a Category 1 to a Category 3 storm in a matter of hours. No one saw it coming. In many cases, that lack of information translates to a lack of preparedness, making it difficult for local officials to know when to issue evacuation orders or where to place resources ahead of a storm.
CYGNSS solves the rain problem with a clever use of the same technology that guides you while you’re driving or lets you “check in” at your local pizza place. Global positioning system (GPS) satellites are sending out signals all over Earth all of the time, allowing a smart phone, for instance, to simply grab a few of these signals and instantly triangulate its position based on Doppler shifts in the signals’ frequencies. CYGNSS detects GPS signals—which are much longer wavelength than those of weather satellites, and therefore unaffected by rain—as they’re reflected off the ocean surface beneath a storm. The satellite’s onboard computer then measures how distorted the signals have become by the waves. The choppier the water, the more distortion, and the more distortion, the windier it must be at the surface. The result is a set of wind speed measurements across the whole storm area, and therefore an accounting of a storm’s energy at the surface.
Because it consists of eight micro-satellites, each about the size of a full-grown swan (hence the acronym), and each able to take four measurements of the sea surface at a time, the CYGNSS network can cover a lot more territory than the single aircraft and satellites that currently monitor hurricanes. The CYGNSS fleet will take data across the entire tropics every seven hours. While it’s not yet clear how much more accurate CYGNSS will make storm classification, some early models show intensity predictions doubling in accuracy.
Ruf, a remote sensing specialist at the University of Michigan, came up with the concept for CYGNSS after a colleague asked him whether fleets of small, cheap satellites sampling several locations apiece could be useful in studying weather. Ten years earlier, the answer would probably have been no. But now that GPS receivers are designed to be pocket-small and to run off the likes of a smart phone battery, the idea had merit.
“When we started looking into the technology side of it, realizing how low-power these receivers were, then everything just fit together,” says Ruf.
CYGNSS is the first in a new line of NASA spacecraft—officially named Earth Venture—meant to improve space-borne observations of Earth using cheaper, simpler technologies. Everything on the CYGNSS spacecraft, except for its computer and accompanying software, is a commercial, off-the shelf component. The entire mission will cost a little over $160 million, compared with billions for larger spacecraft. Missions like CYGNSS are also much more streamlined; Ruf says the bigger NASA missions can be 15 years in the making, while the CYGNSS project has taken less than six years from concept to launch.
In addition to improving intensity forecasting, the new data soon to be gathered by CYGNSS could help solve many of the theoretical questions still nagging hurricane scientists, such as how and why tropical storms form in the first place. In some ways, atmospheric scientists are still looking for the right questions to ask, so they’re eager to see what patterns emerge in the data.
“There’s a whole bunch of people on the science team that are basically trying to figure out how best to use this new data,” says Ruff.
In the meantime, we’ll be going into next hurricane season with a much better warning system.