New Instrument Images Daytime Aurora
The northern lights, or aurora, are well known to citizens of our planet that live near the polar regions. These shimmering curtains of light have been the source of many fanciful stories told during long winter nights. Aurora occur when electrons and ions streaming off of the Sun strike molecules in the Earth's upper atmosphere and cause them to glow with colors that are characteristic of the molecules themselves. The light produced by aurorae is usually far too faint to be seen in daylight but with a cleverly designed camera scientists are now doing just that.
The Ultraviolet Imager (UVI) uses a specially designed camera to filter out all of the light except that emitted by the aurorae themselves. The camera and its electronic support package were manufactured, assembled, and tested at Marshall Space Flight Center in a joint effort with the University of Alabama, Huntsville and Science and Engineering Associates in Huntsville. The camera was mounted on the POLAR spacecraft and launched into orbit on a Delta II rocket on February 24, 1996 from Vandenberg Air Force Base, California. The POLAR satellite is now orbiting the Earth in a path that takes it from 2 Earth radii out to 9 Earth radii and back every 18 hours. Ten other instruments are included on this mission to measure particles and electro-magnetic fields in the high-latitude polar regions. Dr. James Spann, a co-investigator for UVI, notes that a prime objective for the POLAR mission is to provide auroral images that show where energy is being deposited into the Earth's upper atmosphere and ionosphere.
Aurora have been seen at nighttime from space by Space Shuttle astronauts. These ribbons of light seem to rise up out of the Earth's upper atmosphere along arcs that disappear over the horizon.The electrons and ions that form the solar wind stream past the Earth at speeds in excess of 1 million miles per hour. These electrically charged particles get caught in the web of the Earth's magnetic field and flow down into the atmosphere where the magnetic field lines enter the Earth. The energy associated with this flow is equivalent to as much as 100 million kilowatts of energy each day.
The Ultraviolet Imager produces pictures of the aurora that show the footpoints of these flows even on the daylit side of the planet. From the high vantage point of the POLAR spacecraft the auroral arcs are seen to form ovals that encircle each of the Earth's magnetic poles. In the image shown below a nearly complete auroral oval can be seen even though this image was obtained near the time of the summer solstice when the entire north polar region is fully sunlit. The north pole is at the center of the image and the bright aurora at the bottom is located over northern Alaska. These images will help to quantify the overall effects of solar energy input to the Earth's polar regions. Daily images can be viewed at the UVI Picture-of-the-Day site.
For more information, please contact
Dr. Jim Spann
NASA/Marshall Space Flight Center
Huntsville AL 35812