Applied Physics Laboratory
Johns Hopkins University
Laurel, Maryland

4 June 1998

APL SCIENTISTS MAKE SURPRISING DISCOVERY ABOUT AURORAS

As was reported in the May 28, 1998, cover story of Nature, scientists from The Johns Hopkins University Applied Physics Laboratory (APL) have made a surprising discovery that contradicts long-held beliefs about the sun's relationship to the aurora. Contrary to observations dating back more than 200 years, APL physicists Patrick Newell, Ching Meng, and Simon Wing have concluded that intense auroras occur more frequently when less energy is being released from the sun during its magnetic field's 11-year cycle, rather than near the peak of its solar activity.

During this peak, often referred to as solar maximum, great amounts of energy are released that can produce magnetic storms in the Earth's ionosphere. Until now, scientists have believed that auroras occur more frequently during this time of increased solar activity.

The research findings benefit both the scientific community and the general public, according to Newell. "Our discovery may help us narrow down the actual cause of auroras," says Newell. "It will lead to a better understanding of their effect on upper atmospheric weather. And, it will help tourists traveling to Alaska and other high-latitude locations plan their trips to see the grand 'northern lights' during optimum viewing times."

The APL scientists confirmed an existing theory regarding how auroras are created, called the ionospheric conductivity feedback mechanism. This theory implies that during solar maximum, when the sun's ultraviolet rays increase ionospheric conductivity, there should be fewer intense auroras, at least under sunlit conditions. The theory predicts no change in auroral frequency during conditions of darkness.

To test this theory, Dr. Newell and his colleagues conducted the first-ever statistical study of an entire solar cycle using 12 consecutive years of charged particle data from Air Force Defense Meteorological satellites. "The data from the Air Force satellites confirmed our assumptions based on the ionospheric theory, and support the idea that intense auroras are a discharge phenomenon, analogous to lightning," says Newell. He adds, however, that rare, huge magnetic storms, which allow auroras to be seen at lower-than-usual latitude, are still more common following solar maximum, but they only represent a small fraction of the total number of intense auroras.

To read more about the auroral research by Dr. Newell and his colleagues, visit the following Web site: http://sd-www.jhuapl.edu/Aurora.

The Applied Physics Laboratory is a not-for-profit laboratory and independent division of The Johns Hopkins University. APL conducts research and development primarily for national security and for nondefense projects of national and global significance. Located midway between Baltimore and Washington, D.C., in Laurel, Md., APL employs 2,700 full-time staff.

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