— Tropical depressions are known to lurk under cloud cover before emerging into view as the destructive seeds of a hurricane. The cloud cover has long crimped forecasters efforts to warn of developing hurricanes.
But two NASA satellites, originally deployed to track climate, are now helping meteorologists see through the clouds and detect these young storms.
Getting the Picture
“If [a depression] is below a high canopy of clouds, many times we didn’t even know it was there,” says Evan Forde, an oceanographer at NOAA’s Atlantic Oceanographic and Meteorological Laboratory.
Hurricane forecasters have begun using microwave technology from the two satellites to peer through cloud cover and view the underlying weather conditions that drive hurricanes: wind and rainfall. Data from NASA’s Quikscat satellite, determines wind speed and direction while data from the Tropical Rainfall Measurement Mission satellite (TRMM) provides information about the amount of rainfall in a given area.
Quikscat works by using a device called a scatterometer that sends beams of microwave radiation down at an angle to the ocean surface below. A rough ocean bounces the scattered beams back to the satellite; the more scattered the beams, the rougher the seas. The scatterometer also detects the direction of the wind, to see if it is blowing in a complete circle, which indicates a tropical depression.
Military, Sea-Faring Use
Timothy Liu, project scientist for the Quikscat mission at NASA’s Jet Propulsion Laboratory, says the satellite, launched last year at the cost of $19 million for the entire mission, was designed to study how ocean currents affect global climates. Quikscat provides forecasters with enough information to identify the early signs of swirling storms 46 hours, or almost two days, before previous data, according to NOAA scientists. And when the orbits of the Quickscat and TRMM satellites overlap, their wealth of data offer an unusually clear picture of the swirling vortexes of hurricanes.
Early detection is important for weather forecasters, who must track and issue advisories for storms over wide stretches of ocean, but also to the sea-going community that depends on storm warnings for it’s livelihood.
“Earlier this year, 18 people died when they got caught in Hurricane Carlotta” out in the Atlantic Ocean, says James Franklin, a hurricane specialist at the National Hurricane Center. “There are fishermen and military assets out in the ocean that need this information.” He says that while ocean storms don’t affect the general public, there is a great need to know where systems are forming.
No Need to Piece It Together
What makes Quikscat even more valuable is its broader range of coverage. Unlike most weather satellites, which capture only about 250 mile strips of the Earth at a time, Quikscat blankets huge 1,000 mile swaths of ocean in one sweep. That amounts to a daily coverage of 90 percent of the Earth’s ice-free oceans, according to NASA. The result is it can provide forecasters with one overall picture of a storm, rather than snapshots that they must piece together.
“Floyd was such a huge and scary storm,” says Forde, “and you could only see a part of it every couple days. It was the size of Florida. Now we can see the whole storm at one time.”
The new technology may offer better coverage, but Franklin says flying airplanes into the eyes of storms remains the most accurate way of diagnosing hurricanes and judging when they’re close to land. Still, the new Quikscat data allows the National Hurricane Center more time to prepare for storms as they approach.
Satellites, however, don’t live forever. Liu says the expected life span of Quikscat is about three years, although satellites can last as long as 10 years depending on the battery and how much they deteriorate from radiation. Plus, Liu says NASA plans to launch another scatterometer in November 2001, this time aboard a Japanese satellite.
By then, scientists may even have found more ways to use the new data. As Forde says, “We’re just scratching the surface of what can be down with a tool like this.”