Dec 6 2012
From The Space Library
RELEASE: 12-424 FERMI IMPROVES ITS VISION FOR THUNDERSTORM GAMMA-RAY FLASHES
WASHINGTON -- Thanks to improved data analysis techniques and a new operating mode, the Gamma-ray Burst Monitor (GBM) aboard NASA's Fermi Gamma-ray Space Telescope is now 10 times better at catching the brief outbursts of high-energy light mysteriously produced above thunderstorms. The outbursts, known as terrestrial gamma-ray flashes (TGFs), last only a few thousandths of a second, but their gamma rays rank among the highest-energy light that naturally occurs on Earth. The enhanced GBM discovery rate helped scientists show most TGFs also generate a strong burst of radio waves, a finding that will change how scientists study this poorly understood phenomenon. Before being upgraded, the GBM could capture only TGFs that were bright enough to trigger the instrument's on-board system, which meant many weaker events were missed. "In mid-2010, we began testing a mode where the GBM directly downloads full-resolution gamma-ray data even when there is no on-board trigger, and this allowed us to locate many faint TGFs we had been missing," said lead researcher Valerie Connaughton, a member of the GBM team at the University of Alabama in Huntsville (UAH). She presented the findings Wednesday in an invited talk at the American Geophysical Union meeting in San Francisco. A paper detailing the results is accepted for publication in the Journal of Geophysical Research: Space Physics. The results were so spectacular that on Nov. 26 the team uploaded new flight software to operate the GBM in this mode continuously, rather than in selected parts of Fermi's orbit. Connaughton's team gathered GBM data for 601 TGFs from August 2008 to August 2011, with most of the events, 409 in all, discovered through the new techniques. The scientists then compared the gamma-ray data to radio emissions over the same period. Lightning emits a broad range of very low frequency (VLF) radio waves, often heard as pop-and-crackle static when listening to AM radio. The World Wide Lightning Location Network (WWLLN), a research collaboration operated by the University of Washington in Seattle, routinely detects these radio signals and uses them to pinpoint the location of lightning discharges anywhere on the globe to within about 12 miles (20 km). Scientists have known for a long time TGFs were linked to strong VLF bursts, but they interpreted these signals as originating from lightning strokes somehow associated with the gamma-ray emission. "Instead, we've found when a strong radio burst occurs almost simultaneously with a TGF, the radio emission is coming from the TGF itself," said co-author Michael Briggs, a member of the GBM team. The researchers identified much weaker radio bursts that occur up to several thousandths of a second before or after a TGF. They interpret these signals as intracloud lightning strokes related to, but not created by, the gamma-ray flash. Scientists suspect TGFs arise from the strong electric fields near the tops of thunderstorms. Under certain conditions, the field becomes strong enough that it drives a high-speed upward avalanche of electrons, which give off gamma rays when they are deflected by air molecules. "What's new here is that the same electron avalanche likely responsible for the gamma-ray emission also produces the VLF radio bursts, and this gives us a new window into understanding this phenomenon," said Joseph Dwyer, a physics professor at the Florida Institute of Technology in Melbourne, Fla., and a member of the study team. Because the WWLLN radio positions are far more precise than those based on Fermi's orbit, scientists will develop a much clearer picture of where TGFs occur and perhaps which types of thunderstorms tend to produce them. The GBM scientists predict the new operating mode and analysis techniques will allow them to catch about 850 TGFs each year. While this is a great improvement, it remains a small fraction of the roughly 1,100 TGFs that fire up each day somewhere on Earth, according to the team's latest estimates. Likewise, TGFs detectable by the GBM represent just a small fraction of intracloud lightning, with about 2,000 cloud-to-cloud lightning strokes for every TGF. The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership and is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States. The GBM Instrument Operations Center is located at the National Space Science Technology Center in Huntsville, Ala. The GBM team includes a collaboration of scientists from UAH, NASA's Marshall Space Flight Center in Huntsville, the Max Planck Institute for Extraterrestrial Physics in Germany and other institutions.
MEDIA ADVISORY: M12-235 THREE NASA AIRBORNE EARTH SCIENCE MISSIONS FOCUS OF JAN. 25 MEDIA DAY
WASHINGTON -- NASA is inviting media to look behind-the-scenes at several active Earth science missions that will take to the air next month to study climate change and air pollution. These airborne missions are all based at NASA's Dryden Flight Research Center in Southern California. On Jan. 25, journalists will have the opportunity to meet with mission scientists to find out how they are using airborne instruments in conjunction with satellite observations to advance our understanding of complex Earth systems. Tours of mission operations and NASA research aircraft will be provided at the Dryden Aircraft Operations Facility in Palmdale, Calif., and at Dryden's main campus on Edwards Air Force Base. The three major Earth Science missions highlighted during the day-long media opportunity will be probing air pollution across central California and key climate change unknowns high over the tropical Pacific Ocean. Two of NASA's high-altitude aircraft, the unmanned Global Hawk and the ER-2, are among the planes that will fly during these missions. The multi-year DISCOVER-AQ campaign will fly NASA's P3B and B200 King Air planes over California's San Joaquin Valley to measure air pollution this winter. The mission seeks to improve the monitoring of pollution from satellites so that scientists can produce better air-quality forecasts and more accurately identify pollution sources. The Airborne Tropical Tropopause Experiment campaign focuses on the region of the upper atmosphere where pollutants and other gases enter the stratosphere and potentially influence our climate. A key focus of the mission is water vapor, which can significantly impact Earth's energy budget, ozone layer and climate. The Polarimeter Definition Experiment campaign will fly several of a new breed of instruments that scientists plan to fly in space one day to improve our measurements of aerosols and clouds. Aerosols, tiny particles produced across the world from many different sources, influence Earth's climate and can affect human health. Scientists and aircraft from two other NASA Earth science missions preparing for flights later this year also will be available for interviews and tours. The Uninhabited Aerial Vehicle Synthetic Aperture Radar, flying aboard a NASA C-20A piloted aircraft, is used to study earthquakes, volcanoes, oil spills, landslides and glacier movements. The Air Surface Water Ocean Topography campaign is testing instruments for a future spacecraft mission that will make the first-ever global survey of Earth's surface water. Media requests for event credentials should be submitted via email to NASA Dryden's public affairs office at DrydenPAO@nasa.gov or by phone to 661-276-3449 no later than Dec. 17 for foreign nationals and Jan. 11 for U.S. citizens and permanent resident aliens. Media representatives wishing to participate must be on assignment with a verifiable media organization. No substitutions of non-credentialed personnel will be allowed. U.S. citizens must provide full name, date and place of birth, media organization, the last six digits of their social security number and their driver's license number and state of issue. In addition, foreign nationals must list their country of citizenship and visa or passport number with the country of issue and expiration date.
