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Where? -- does it occur
The spatial distribution of auroral emissions
on a global scale. This falsecolor image of the northern auroral oval at vacuum-ultraviolet wavelengths is overlaid with
a coastline map to show how the nearly instantaneous auroral oval maps onto the polar regions. The noncircular
distribution of luminosities arises in large part from the non-dipolar components of the magnetic field, and
is observed to rotate diurnally. Indeed, a trained observer can estimate Universal Time by studying the
instantaneous spatial distribution of auroral emissions. The noncircular nature of this distribution is less prominent
in the southern polar region. In magnetic coordinates these spatial distributions are nearly circular
in both hemispheres. This image was obtained with the University of Iowa's auroral imaging instrumentation
during the 12-minute period beginning at 0229 UT on 8 November 1981, about seventy minutes after the arrival
at Earth of a shock in the interplanetary medium. The sensitivity passband of the ultraviolet wavelength
photometer for this image extends from 123 to 155 nm. Auroral emissions at these wavelengths arise predominantly
from the emission lines of atomic oxygen at about 130.4 and 135.6 nm and from the Lyman-Birge-Hopfield
bands of molecular nitrogen. These emissions rival in intensities the emissions from the sunlit hemisphere
at large solar zenith angles as seen here in the upper left portion of the image. The auroral oval approaches
the terminator at local noon.
Where to find the
Where the aurora is visible in the northern hemisphere -- 100
nights a year on the "100" oval, 10 nights a year on the "10" oval,
and so forth. From University of Alaska.
Variation in the size of the auroral oval with
activity. The shaded area represents the distribution of maximum
auroral activity in the northern hemisphere. Coordinate system is
corrected geomagnetic (CG) latitude and CG local
time, and noon is at the top. Adapted from Feldstein and Starkov,
Dynamics Explorer 1989 Event:
The left image is an extremely large aurora that
occurred 14 March 1989 at 0151 UT over the southern polar regions and the
right image is a re-mapping of that image along magnetic field lines to
the northern polar regions. This is a close approximation of what the auroral
oval probably looked like if DE-1 had been over the northern hemisphere
at this time.
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Last updated: 7/26/00
Above is background material for archival reference only.