Volume: 02, Issue: 13 07/21/2004 
The Altus II research vehicle. Photo courtesy NASA/MSFC.
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A scientific instrument mounted on a NASA WB-57 research aircraft measures the size and mass of condensed water droplets and ice particles as the jet flies through cirrus clouds. Photo courtesy Jay Mace, University of Utah.
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Other Articles in This Issue:
Chasing the Storm
Satellites and Radar Track Devastating Storms
Scientist Sees Lightning like Superman
Enhance Your Storm Experience
Chase Storms in Your Classroom

Aircraft Hunt for Weather Clues

Since the Wright Brothers’ first flight more than 100 years ago, aircraft technology has evolved and flourished, being used for various purposes, both civilian and military. Scientists have also made excellent use of this technology: both piloted and unmanned aircraft have soared above Earth to study weather and climate activity in the skies.

In 2002, NASA and university scientists put the latest flight technology to use, sending a remotely piloted aircraft soaring to heights of more than 50,000 feet to study lightning. The high-flying aircraft, packed with data-gathering instruments, enabled scientists conducting the Altus Cumulus Electrification Study (ACES) to study electrical storms without the human risks.

"Much has changed in 250 years since Franklin proved lightning carries an electrical charge," said principal investigator Dr. Richard Blakeslee, a NASA atmospheric scientist at the Global Hydrology and Climate Center in Huntsville, Ala. "Only recently have we acquired the ability to get an up-close, comprehensive look at storms without risking human contact with the energetic forces of nature."

Based at the Naval Air Facility Key West in Florida, the storm-hunter research team flew 11 science missions, making 115 passes over the tops of thunderstorms to gather a multitude of data. One of the study's goals, Blakeslee said, was to test new aircraft technology and determine its potential for future meteorological applications.

"A challenge weather researchers often face is getting continuous coverage of a single storm," he said. "An aircraft flying at 200 mph, for example, would provide only brief snapshots of storm activity sandwiched between long periods with no observations."

To overcome these challenges, the research team used the General Atomics Aeronautical Systems, Inc. Altus II twin turbo uninhabited aerial vehicle, often called a UAV. Chosen for its slow flight speed of 70 to 100 knots (80 to 115 mph) and high-altitude flight (up to 65,000 feet), the Altus boasts a wing span of 55 feet and can monitor the storms on a near-continuous basis.

"During this study, we made multiple storm passes in much shorter time periods than ever before, proving it is possible to make nearly continuous observations of severe weather," Blakeslee said.

Evidence of this success was apparent when the aircraft was able to stay over and around a single storm for one hour and 20 minutes. "For this one storm alone, we gathered data on more than 500 optical and electrical events produced by lightning flashes," Blakeslee said.

"We gathered a vast amount of scientific information throughout August, and each flight taught us something new about the aircraft's capabilities," said project manager Tony Kim of NASA's Marshall Space Flight Center in Huntsville.

The results of this experiment help validate the use of remotely piloted aircraft for atmospheric research as well as scientific research in other areas. Part of NASA's Uninhabited Aerial Vehicle-based science demonstration program, these flights acted as a proving ground for future uses, such as carrying Earth-viewing scientific payloads into environments where pilots would be exposed to potentially life-threatening hazards.

Data acquired during the research flights included electric, magnetic, and optical measurements, enabling the scientists to gauge elements such as lightning activity and the electrical environment in and around the storms. To complement this data, ground-based sensors gathered additional information, such as the lightning flash rate, amount of precipitation, and speed of updrafts, while satellite imagery provided a view of the storms from high above.

By learning more about individual storms, scientists also hope to lend new insight into the global water and energy cycle and climate variability, while providing federal, state and local governments with new disaster-management information for use during severe storms, floods and wildfires.

Unmanned aircraft are not the only ones used to study weather and climate patterns, however. In 2004, a group of meteorologists from the University of Utah are using a piloted NASA research jet to examine icy, wispy cirrus clouds high in the atmosphere. The study is aimed at determining how much the clouds warm Earth’s climate and how much they cool it.

“This experiment involves measuring cirrus clouds, and ultimately will help us understand the mechanisms of climate change,” said Jay Mace, an associate professor of meteorology at the university and mission scientist for the project, which is sponsored by NASA.

During the Middle Latitude Cirrus Experiment (MidCiX), Mace is working at Ellington Field near Houston, helping guide a NASA WB-57 jet plane on flights through cirrus clouds 25,000 to 35,000 feet above north-central Oklahoma.

“I’m directing the operation from the ground,” said Mace, who watches satellite images of cirrus clouds to help the NASA WB-57 pilot find the clouds.

Mace said the flights are designed so that data about the same cirrus clouds can be collected simultaneously by a dozen scientific instruments on the WB-57 aircraft, which is a high-altitude jet with a 122.5-foot wingspan, capable of flying to 60,000 feet elevation or more. It is a converted version of the B-57 Canberra aircraft, various versions of which were used for combat bombing, aerial spying, weather reconnaissance, and sampling for radiation from suspected atmospheric nuclear weapons tests.

Cirrus are the highest-elevation clouds involved in weather and cap the portion of the atmosphere where weather occurs: the troposphere, which extends from Earth’s surface to 40,000 feet. Cirrus clouds are so high that they are made mostly of ice crystals rather than water droplets. As the WB-57 flies through the clouds, various instruments sample, measure, or take pictures of the ice crystals.

According to Mace, cirrus clouds typically have “the appearance of filaments or streaks. They are often described as mare’s tails. Often they are harbingers of bad weather in two to three days. They are blown in on a jet stream and tend to arrive before the rest of the weather does.”

Most scientists believe carbon dioxide from industrial society’s combustion of oil and other fossils fuels is gradually warming Earth’s climate, and they have devised computer simulations or “models” to better predict the extent and timing of global warming. But cirrus clouds pose a major uncertainty in such simulations because they can both warm the climate by trapping heat that otherwise would escape to space and cool the climate by reflecting sunlight back into space.

Lower-elevation clouds mainly reflect sunlight to cool climate but do not trap heat like cirrus clouds do. “Cirrus clouds are like blanket,” Mace said. “They hold the heat in, yet they allow a lot of the sunlight though. That’s why they have the ability to warm climate.”

The MidCiX experiment is designed to gather detailed information about cirrus clouds to improve the accuracy of computer simulations of future climate change.

“There is great scientific debate about the simple question: ‘What are the sizes of ice crystals in cirrus clouds?’” said Tim Garrett, assistant professor of meteorology at the University of Utah. “The answer to this question has potentially very large implications for our models of how much of the Earth’s heat cirrus clouds trap and how much sunlight they reflect. MidCiX is addressing this question using an unprecedented array of the latest cloud physics instrumentation.”

Details of the Middle Latitude Cirrus Experiment (MidCiX) may be found at:

The Altus Cumulus Electrification Study is a collaboration of the Marshall Center, the University of Alabama in Huntsville, NASA's Goddard Space Flight Center in Greenbelt, Md., NASA's Ames Research Center at Moffett Field, Calif., Pennsylvania State University in University Park, and General Atomics Aeronautical Systems, Inc. in San Diego. The Global Hydrology and Climate Center is one of seven science research centers at the National Space Science and Technology Center (NSSTC) in Huntsville. The NSSTC is a partnership with the Marshall Center, Alabama universities, industry and federal agencies.

Visit the following websites for further information:

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