Rice University
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News Release
CONTACT: B.J. AlmondPHONE: (713) 348-6770
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DYNAMICS OF AURORAS AT NORTH AND SOUTH POLES STUDIED SIMULTANEOUSLY FOR FIRST TIME
Rice University professor to present findings at American Geophysical Union meeting Dec. 13
HOUSTON – Dec. 12, 2001 – For the first time, the entire sequence of an auroral storm has been studied simultaneously over both hemispheres, yielding information that might help scientists issue warnings about potentially harmful storms.
The study is reported in a paper that will be presented Thursday at the American Geophysical Union meeting in San Francisco by Patricia Reiff, director of the Rice Space Institute at Rice University in Houston. She will interpret images of aurora borealis, the aurora around the north pole, and aurora australis, the corresponding aurora around the south pole, taken Aug. 17 this year by the IMAGE and Polar NASA satellites, respectively.
"The question we’ve been wanting to answer is whether the southern and northern auroras are conjugate or anticonjugate," said Reiff, a professor of physics and astronomy at Rice.
Previous studies have indicated that auroras inside the polar caps are anticonjugate, or opposites; a high latitude aurora observed on the dawn side of the northern hemisphere would be accompanied by a "mirror image" on the dusk side of the southern hemisphere. Lower latitude auroras in the main auroral oval have been known to be nearly conjugate, or appearing in nearly the same local time and latitude in both hemispheres.
But images of the auroras taken during a geomagnetic storm Aug. 17 were nearly conjugate; the highest-latitude auroras appeared on the dusk side of both polar caps.
Auroras occur when electrons and protons that are trapped in Earth’s magnetic field hit the gases of Earth’s upper atmosphere. Those electrical particles can move only along the invisible magnetic field lines that are connected to Earth near the north and south poles. When the magnetic field is energized by a storm, the particles travel to both ends of the field lines, creating bright auroral displays of streamers or arches of light in rings measuring 2,500 miles in diameter around each pole.
Reiff said the auroras observed Aug. 17 were actually anticonjugate early in the storm when the polar cap was connected to the solar wind. The very large dawn-dusk component of the interplanetary magnetic field pulled the open field lines to the dusk in the southern hemisphere and toward the dawn in the northern hemisphere. But once the storm got started and the electrical particles were blasted by Earth’s magnetic tail, the auroras were conjugate, as evidenced by both the northern and southern auroral displays being brightest at the same magnetic locations at the same time. The aurora is nearly symmetric when mapped in magnetic coordinates, not in geographic coordinates. Reiff was able to observe these changes as they occurred because the images taken by both spacecraft were produced in a real-time mode and available to the public through the Space Environment Center.
This finding could be particularly useful when scientists need to issue warnings in real time about potentially dangerous auroras, Reiff said. If the main auroral oval is found over populated areas, it has the potential to trip electrical circuits and destroy transformers. The poleward edge of the aurora also marks the "danger zone." Astronauts or high-altitude pilots who fly poleward of the aurora can be in danger if there is a solar energetic-particle event in progress.
"If we can trust that the aurora in the northern hemisphere is the same as in the southern hemisphere, we can use imagers over either pole as our monitors," Reiff said. "This will enable us to predict where the northern aurora will be located based on its appearance in the south, or vice versa."
She added, however, that although the large-scale aurora is nearly conjugate, including undulations at the poleward edge, the hemispheres have significant differences. "There’s still a lot more to be learned," she said. "Some of the details may be caused by near-Earth instabilities that can be different in the two hemispheres. This study, like others previously, was serendipitous, based on a happy accident of orbit and timing. A pair of spacecraft designed to monitor both poles simultaneously would be ideal to discover how much of the structure is locally determined."
Reiff is lead author of the paper, which she co-wrote with Harald Frey and Steve Mende at the University of California, Berkeley, and John Sigwarth and Louis Frank at the University of Iowa, Iowa City. Others who participated in the study were Terry Onsager of the Space Environment Center at NOAA in Boulder and Jerry Goldstein at Rice. The principal investigator of the IMAGE mission is J.L. Burch of Southwest Research Institute, and the Polar spacecraft is managed by the Goddard Space Flight Center in Greenbelt, Md.
Images and movies from Reiff’s talk will be available on the Web at http://www.spaceupdate.com/IMAGE/News121201.html. A CD-ROM, "Space Weather," which describes the science of space weather and highlights of the IMAGE mission, will be distributed.
LINKS:
IMAGE/Polar movie in quicktime format : (35 MB) Features are mapped to magnetic coordinates
IMAGE/Polar movie in avi format (not as good quality): 21 MB
IMAGE/Polar image of asymmetric polar cap 1704 UT; smaller version
IMAGE/Polar image of duskside high latitude arc 1753 UT; smaller version
IMAGE/Polar image of auroral expansion 1823 UT; smaller version
IMAGE/Polar image of detailed correspondence of auroral features, including gaps in the aurora 1852 UT; smaller version
IMAGE/Polar image of detailed correspondence of auroral features 1856 UT; smaller version
IMAGE mission home page at Goddard Space Flighte Center
ISTP mission home page at Goddard Space Flighte Center
ISTP mission home page at Goddard Space Flight Center
Link to conjugate aurora press release
"Space Weather" website at NCAR
"SpaceWeather.com" website
