Auroras In Daylight? APL Scientists Solve Mystery

August 26, 1996

Does the aurora borealis, the grand "northern lights" of the night sky, also shine in daylight when it can't be seen? Researchers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., have a surprising answer to that long-standing scientific question.

"Auroras have been studied for centuries, but always in darkness, when observation was possible," says APL physicist Patrick T. Newell. "It has long been assumed that auroras, like stars, are still present when the sun is up, just hidden."

Not so, according to a report by Newell and APL colleagues Ching-I. Meng and Kevin M. Lyons in the June 27, 1996, issue of the journal Nature. They conclude that the northern lights are present predominantly in darkness, most often between sunset and midnight, and mainly during the spring, winter, and fall months of short days and long nights. This is contrary to the belief that auroral storms usually occur symmetrically in the northern and southern hemispheres.

The APL results were based on scrutiny of more than 150 million measurements made by five U.S. Air Force weather satellites from 1983 to 1992. In order to overcome the problem of observing auroras in daylight, the researchers instead looked at beams of hot electrons from near-Earth space, which can be studied equally well in daylight or darkness. Auroras are thought to originate when those beams of high-speed charged particles from the sun interact with Earth's powerful magnetic field.

The findings also provide strong support for an existing theory that explains the mechanism of aurora formation. One of at least 22 competing theories in the field of auroral research, this explanation contends that auroral intensity correlates to the level of electrical conductivity in the ionosphere.

During sunlit hours, conductivity is high and the electrical circuit between the ionosphere and the energetic particle beams from near-Earth space is stable. But ionospheric conductivity drops at night, particularly on winter nights. This creates instabilities in current flow between the beams and the ionosphere, leading to violent arcing, or electrical discharge -- the aurora -- similar to a lightning flash.

"Our observations strongly support the view that ionospheric conductivity is the key factor controlling the occurrence of discrete auroras," says Newell.


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 non-defense projects of national and global significance. Located midway between Baltimore and Washington, D.C., in Laurel, Md., APL employs 2,800 permanent staff.

To schedule interviews with APL researchers, please contact Luther Young, Office of Communications and Public Affairs, (301) 953-6268 / luther.young@jhuapl.edu. Additional information and color graphics illustrating the auroral study and other APL magnetospheric and ionospheric physics research projects can be accessed on the World Wide Web at:
http://sd-www.jhuapl.edu/Aurora/hp.eng.html

APL news releases are available on the APL external website at:
http://www.jhuapl.edu/.
Also on the Johns Hopkins University site at:
http://www.jhu.edu:80/news_info/news/.

Johns Hopkins University Applied Physics Laboratory

Related Aurora Articles from Brightsurf:

Aurora-chasing citizen scientists help discover a new feature of STEVE
A new finding about the formation of streaks within the aurora-like STEVE phenomenon brings scientists one step closer to solving the mystery.

A cancer shredder
Researchers at the universities of W├╝rzburg and Frankfurt (Germany) have developed a new compound for treating cancer.

Comet Chury's ultraviolet aurora
On Earth, auroras, also called northern lights, have always fascinated people.

SwRI instruments aboard Rosetta help detect unexpected ultraviolet aurora at a comet
Data from Southwest Research Institute-led instruments aboard ESA's Rosetta spacecraft have helped reveal auroral emissions in the far ultraviolet around a comet for the first time.

Aurora mysteries unlocked with NASA's THEMIS mission
A special type of aurora, draped east-west across the night sky like a glowing pearl necklace, is helping scientists better understand the science of auroras and their powerful drivers out in space.

Alaskan seismometers record the northern lights
Aaron Lojewski, who leads aurora sightseeing tours in Alaska, was lucky enough to photograph a ''eruption'' of brilliant pink light in the night skies one night in February.

Resurrecting ancient protein partners reveals origin of protein regulation
After reconstructing the ancient forms of two cellular proteins, scientists discovered the earliest known instance of a complex form of protein regulation.

Newfound Martian aurora actually the most common; sheds light on Mars' changing climate
A type of Martian aurora first identified by NASA's MAVEN spacecraft in 2016 is actually the most common form of aurora occurring on the Red Planet, according to new results from the mission.

Martian aurora offers climate change clues, Embry-Riddle reports
A newly published study reveals that a type of Martian aurora originally detected by NASA's MAVEN spacecraft is in fact the most common aurora on the Red Planet, Embry-Riddle Aeronautical University researchers said.

How newly found tension sensor plays integral role in aligned chromosome partitioning
A Waseda University-led research found that oncogene SET/TAF1, which was found to be a proto-oncogene of acute myeloid leukemia (AML), contributes to proper chromosome partitioning as a tension sensor.

Read More: Aurora News and Aurora Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.