Technology Transfer

NASA Provides Insight to Understanding Hurricanes

THROUGHOUT HISTORY, IT SEEMS THAT humans have been obsessed with understanding, predicting, controlling and influencing the weather. Exploring the atmosphere through its space program, NASA is a key player in showing that weather prediction is a science with many life-saving and cost-saving benefits.

With an aim to better understand and improve ground-based predictions of hurricanes, two specially equipped NASA aircraft—a converted spy plane and a refitted jetliner—took weather researchers on a historic ride into the eye of Hurricane Bonnie in August 1998. The intent of the researchers was to collect high-altitude information about Atlantic hurricanes and tropical storms for more insight into hurricane structure, dynamics and motion.

The Birth of a Hurricane

Sunlight heats the ocean. Water evaporates, rises and forms rain, surrendering its heat to the air and accelerating the rise. Air flows in on the surface to replace rising air, barometric pressure drops and air masses slowly start circling.

The tropical depression becomes a tropical storm, winds grow steadily until they pass the 110-kilometer-per-hour (km/h), or 60-knot, mark and keep rising to 368 km/h (200 knots) or more. A hurricane is born.

The pattern repeated itself as the 1998 hurricane season in the Atlantic Ocean began in mid-August. This year was different, though. For the first time since the 1950s, research scientists looked at the upper levels of the storms, not just the middle and lower altitudes that are braved by hurricane hunter teams.

Why Hurricanes Have More Impact Today

It all comes down to thermodynamics, the physics of heat. Water absorbs energy from the air or sunlight when it goes from sea surface to vapor, and it surrenders energy to the air when it turns vapor to rain drops.

Where the energy changes hands is what powers the hurricane, but hurricanes are no more powerful than before. There are more people living in coastal regions than ever before, and they have built more homes and businesses for hurricanes to destroy. Therefore, the need to understand the mechanics of hurricanes increases each year as human populations grow in coastal areas.

Cutting-Edge NASA Research Could Save Lives and Money

Specially equipped NASA aircraft have taken to the skies—collecting high-altitude information about Atlantic hurricanes and tropical storms—as part of the third Convection and Moisture Experiment (CAMEX-3). This mission may increase warning time, saving lives and property, and decrease the size of evacuation areas, thus saving money.

National Oceanic and Atmospheric Administration (NOAA) officials estimate that improved forecasting can be worth millions of dollars per mile. That is, every inch of coastline that does not have to be alerted avoids a million dollars in lost economic productivity. Until a hurricane's power is more understood, forecasters practice "overwarning" rather than risk a potential sudden "hit" that catches people off guard.

CAMEX-3, designed to study the factors involved in how strong a hurricane grows, is an interagency project to measure hurricane dynamics at high altitude—a method never before employed over Atlantic storms. It operates out of Patrick Air Force Base in Florida. The CAMEX-3 study uses NASA's converted DC-8 and ER-2 high-altitude research aircraft in conjunction with NOAA's WP-3D Orion hurricane hunter and various other instruments. It also uses data from weather satellites and has timed its flights to coincide with observations by the Tropical Rainfall Measuring Mission (TRMM) satellite.

"This is a significant achievement for this hurricane study," said CAMEX-3 project scientist Robbie Hood, mission scientist from NASA's Global Hydrology and Climate Center at Marshall Space Flight Center in Huntsville, Alabama. "We achieved our number one objective, that we could accomplish the tricky maneuver of placing all three NASA and NOAA aircraft in the study of the structure of the same storm at the same time.

"A lot of these instruments either have versions flying on satellites now or are prototypes for new satellites. We're bringing NASA technology to the picture, satellite and remote sensing technology in particular, and we're trying to give the hurricane research community data that they don't have, data at high altitude where their aircraft don't fly.

"The big thing is that we're bringing space flight technology to bear," Hood said. "We can bring NASA technology to an experiment and to help save lives in the future.

"The hurricane community has made great strides in making more accurate forecasts and tracking," Hood said. "But how intense that hurricane's going to be when it hits the shoreline—or why some storms die out and others just keep going and going—is the important factor.

"This is part of ongoing research that NASA is conducting to study the whole Earth and its atmosphere," Hood explained, "but our real goal is to provide data that could be used eventually to save lives."

Eye to Eye and Bonnie Winks

Hurricane Bonnie formed in the Atlantic Ocean in mid-August. On August 23 and 24, teams of weather researchers went on a historic first ride through and over Hurricane Bonnie's eye—the central, open structure that is the focus of a hurricane's power and motion—as she churned in the Atlantic near the Bahama Islands. And, while looking Bonnie in the eye, she winked.

Finally, on August 26, the team probed Bonnie as it hit the North Carolina shore. The jetliner, flying at 11 km (37,000 feet), was joined at the storm by a NASA ER-2 jet overhead at 19.8 km (65,000 feet) and a NOAA WP-3D Orion turboprop at 4.6 km (15,000 feet) for a 7-hour mission. Bonnie did more than cooperate, veering toward the Outer Banks of North Carolina at the last moment, and even posing for pictures.

"We were afraid we were going to miss it," Hood said. "But once we got there it was like it stopped to wait on us. We noticed while we were flying through it, the center of the eye was not moving that much, and for the last part of the flight it was pretty much sitting still.

"This thing was just sitting here, just waiting on us. I don't know if we'll ever be able to catch another one that perfectly."

During the Bonnie study, two co-existing eye walls were explored. The team had excellent coordination in having one NOAA WP-3D Orion on the first eye wall flight, and both Orions plus an Air Force WC-130 Hercules were on the second eye wall penetration, for a total of five aircraft. It was during the second eye wall flight that Bonnie pulled yet another surprise—snow in August. "Right along the eye wall this big dome cloud had come up, and it was shooting ice crystals or snow up, and it was falling on top of the DC-8," Hood explained.

Compelling images of a 59,000-foot storm cloud towering from Bonnie's eye wall were obtained by the TRMM, offering some valuable information to researchers. By comparison, the highest mountain in the world is 29,000 feet, and the average commercial jet flies at barely one-half the height of Bonnie's cloud tops.

Another impressive step was taken when NASA researchers gave Bonnie some eye drops. Ten small tubes containing miniature weather stations were dropped into Bonnie's shifting eye to check her vital signs, wind speeds, barometric pressure and humidity levels. The tiny weather stations dropped into the middle of the eye verified the readings the DC-8 remote-sensing instruments were reading at 11 km (37,000 feet).

Success at the Halfway Mark

Although the scientists are halfway through the flight campaign, they have hardly begun the important work of CAMEX-3: analyzing the data. And they have plenty. "This experiment is going to produce a ton of papers," Hood said.

A campaign to make the most extensive set of hurricane measurements is already a phenomenal success, even though it is only halfway through its flight time. "The Bonnie data set is just incredible," Hood said.

While hurricanes have been probed by aircraft since the 1940s and monitored by satellites since the 1960s, this was the first coordinated campaign to measure a hurricane's growth with aircraft at low, medium and high altitudes. "We're going to push real hard to get the data on-line as soon as possible," Hood said. Browse or summary versions of the data will be available in 3 months, and the first complete data sets will be available starting in 6 months.

The hurricane study is part of NASA's Earth Science Enterprise. Its purpose is to better understand the total Earth system and the effects of natural and human-induced changes in the global environment.

For more information, contact Karen Kafton at the National Technology Transfer Center.
Call: 800/678-9882, E-mail: kkafton@nttc.edu
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High-altitude over-the-top images of Hurricane Bonnie show the eye, eyewall, sea surface and presence of ice particles associated with the heavy rain band shown.

The ER-2 is a converted Cold War–era U-2 spy plane. It provided real-time data downlinks using the same Tracking and Data Relay Satellite System used by the Space Shuttle and Hubble Space Telescope.