Hurricane Georges puts on a light show
More on sprites and jets
Mother Nature treated hurricane researchers to a rare light show as they flew the last mission of the most ambitious hurricane study campaign in the Atlantic Ocean. Rarely seen lightning fields and purple sprites were detected in the eye of the hurricane by the ER-2 pilot as he flew more than 19.8 km (65,000 ft) above the Atlantic.
The third Convection and Moisture Experiment (CAMEX-3) officially ends today, although that's not the end of the program. With an extensive collection of data, the scientists and their colleagues will be busy analyzing what they recorded and extracting a better understanding of how hurricanes form and energize as they move across the ocean.
Right: Georges as seen as it moved from Hispaniola into Cuba shortly this morning by the Advanced High Resolution Radiometer on board the NOAA-12 polar-orbit weather satellite. (Links to . Courtesy of the Ocean Remote Sensing Group at the Applied Physics Laboratory, The Johns Hopkins University, Laurel, Md.)
Above: Sprites are lightning flashes that rise from storms and apparently connect with the upper atmosphere. Their exact origin and nature are mystery. These images were captured by a University of Alaska aircraft studying storm systems over the Midwest in 1994.
Ironically, the team may have to pack quickly and evacuate, with no time for lengthy farewells (the group photos were already done Saturday) because Georges is threatening Patrick Air Force Base on Florida's east coast, where the CAMEX-3 team is based. The evacuation of the Florida Keys has already been ordered.
The hurricane's farewell gift - the lightning and sprites - are a recently discovered phenomenon that NASA's Global Hydrology and Climate Center, coordinator of CAMEX-3, has been studying. Red sprites and blue jets, as they are known, were seen by high-altitude pilots and Space Shuttle crews in the 1980s, perhaps earlier, but most observers were unsure of what they saw and did not report the events. Sprites and jets are very faint and can be recorded only with cameras using image intensifiers (see sidebar).
Observations from the Shuttle in 1989-91 and aircraft videotapes of sprites in 1993 confirmed their existence. The exact cause remains a mystery, although they appear to be a part of the global electrical circuit.
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Tuesday's Georges synoptic/water vapor inflow flight was a success. The hurricane had already made landfall over Hispaniola and was impacting the mountains there. Although Tuesday was the DC-8 Airborne Laboratory's last CAMEX-3 flight - the team sent special thanks to the flight crew for its excellent support.
Monday's Georges eye wall flight was a success. Georges showed many unique characteristics including large cloud turrets, variable eye wall winds, and wind speeds up to 148 km/h (80 knots; 92 mph) at 10 km (33,000 ft) altitude. The eye wall pattern was also significantly displaced from the radar eye wall location unlike those seen with Bonnie, Danielle, or Earl.
Sprites and jets
Reports of strange bursts of colored light coming out of the tops of powerful thunderstorms date back to the 1800s. And even though aircraft pilots reported them in the 1950s and '60s, they remained unconfirmed until recently.
These weird flashes were first observed from the ground, when, quite by accident, they were captured on video on July 5, 1989 by University of Minnesota scientists John Winckler, Robert Franz and Robert Nemzek. The scientists were actually performing a calibration test for a low light level monochrome camera, and weren't particularly looking at the thunderstorm to the east of their observing site at all. The next morning, while viewing the test video, they saw giant twin pillars of light extending upward more than 30 kilometers above the thunderstorm.
The flashes were first recorded from space by the Space Shuttle (STS-34), as it passed over a highly active thunderstorm in northern Australia on Oct. 21, 1989. The shuttle's monochrome TV cameras filmed what are now called sprites and jets. The observations were being conducted as part of the NASA/Marshall Mesoscale Lightning Observation Experiment. Otha H. Vaughan, Jr., of NASA's Global Hydrology Center was the principal investigator.
In 1994, while flying an extremely sensitive color camera normally used for auroral photography in a high altitude aircraft, University of Alaska scientists confirmed that the flashes have a generally reddish color which often fades to purple or blue in the downward extending tendrils. Dr. Davis Sentman of UAF named these "sprites" after the creatures in Shakespeare's "The Tempest," in part because of their transient, ephemeral nature. The UAF team also discovered and named blue jets.
The sprites appear high above the thunderstorm while the jets shoot out from the top of the thunderstorm. Sprites appear to cascade as high as 96 km (60 mi) above the Earth. Sprites can look like giant red blobs, picket fences, upward branching carrots, or tentacled octopi, and can occur singly or in clusters. The jets appear to be ejected from the storm top with velocities as high as 100 km per sec and move up as high as 32 kilometers.
Stratospheric lightning events could generate strong electric fields and electromagnetic pulses which may interact with the Earth's ionosphere and magnetosphere. Strong fields at high altitudes may generate runaway electrons which could then produce high energy x-rays and even gamma rays. Thus, it is possible that lightning may generate a broad spectrum of electromagnetic radiation, ranging from extremely low energy to extremely high-energy gamma radiation. This theory is supported by the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma Ray Observatory which has detected gamma rays coming up from the Earth - not deep space - when the spacecraft was over thunderstorms.
Researchers want to know what effect upward lightning may have on future commercial aviation operations and high altitude balloon research flights in the stratosphere.
What's up there? by Vaughan reviews the history and science of sprites and jets.
Gamma-ray flashes from Earth and sprites and jets - searching for a connection.
Hurricane Georges is smaller than Bonnie, the hurricane that NASA and its partners closely studied earlier this season, but is still quite deadly.
From its first calibration flight on Aug. 8 through today, the CAMEX-3 team - which includes aircraft from the National Oceanic and Atmospheric Administration and coordination with the U.S. Air Force Hurricane Hunters - has studied Hurricanes Bonnie, Danielle, Earl and now, Georges. The project also combined resources and objectives with the Texas and Florida Underflight (TEFLUN-B) campaign in which the same aircraft and instruments measured storms - not necessarily hurricanes - the validate the instruments on the Tropical Rainfall Measuring Mission satellite as it flew overhead.
A complete listing of CAMEX-3 and TEFLUN-B missions is given below.
Note: More details are available in the NASA press release describing CAMEX-3. Check back as hurricane season progresses. We will post science updates as the campaign develops.
PIX: High resolution scans of 35mm camera photos from the CAMEX-3 campaign are available from Public Affairs Office at NASA headquarters. Please call the NASA Headquarters Photo Department at 202-358-1900, or contact Bill Ingalls at firstname.lastname@example.org.
Explanations of sprites and additional images are available from the Global Hydrology and Climate Center and the University of Alaska.
CAMEX Series Headlines
August 12: Overview CAMEX story , describes the program in detail.
August 13: CAMEX maiden flight , for calibration of TRMM satellite instruments
August 14: CAMEX test flights , CAMEX flies over tropical storm weather in successful calibration run
August 18: CAMEX aircraft make second flight with TRMM , second calibration run for TRMM
August 20: CAMEX may get first chance at a tropical storm , later this week
August 21: Here comes Bonnie! , CAMEX scheduled to fly over T.S. Bonnie
August 22: West by Northwest , CAMEX team may have to evacuate to Georgia
August 24: Eye-to-eye, and Bonnie winks, CAMEX team makes first flight through eye
August 25: Snow in August, Bonnie surprises the hurricane team
August 26: Camera of many colors Hurricane hunters using advanced scanner to peer into storms
August 28: Preparing for Danielle NASA team takes break as Bonnie fades away
August 31: Quite a Windfall Hurricane team completes first half of unique science campaign. Includes listing of August flights and aircraft and spacecraft used in CAMEX-3.
September 2: Bonnie Cuts a Towering Figure Satellite radar shows mountainous cloud chimney
September 4: Hurricane team studies Earl Four aircraft probe storm
September 10: NASA team awaits next hurricane
September 16: Hurricane season passing its prime Thunderstorm studies continue as a new hurricane candidate wends its way from Africa.
September 18: Two new storms brewing for hurricane research team Scientists fly 4 out of 5 days, clear air sampled over the Bahamas, oceanic convection data collected east of Cape Canaveral
September 21:The last hurricane - CAMEX team wrapping up campaign with flights into Georges
September 23: Hurricane Georges puts on a light show - CAMEX team treated to purple sprites and weird lightning (this story)
NCAR has an extensive writeup on the GPS dropsondes used in CAMEX-3 and other atmospheric campaigns.
A new study - not related to CAMEX-3 - by the Arizona State University suggests a link between hurricanes in the northwest Atlantic and air pollution.Web Links CAMEX-3 home page contains links to daily flight operations and instrument descriptions.
Lightning Imaging Sensor aboard the TRMM satellite observes lightning from above the clouds - and my lead to better warnings on the ground.
MACAWS uses the Doppler effect (red and blue shifts) to measure wind velocity.
SPARCLE is a Space Shuttle experiment set for 2001 to demonstrate laser wind measurement from space.
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