Where? -- does it occur

• Auroral oval: 
  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 aurora: 
  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.
• Feldstein ovals: 
  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, 1967.
• Large 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.

[Back to the main Aurora page]
 
 

Web development:   Theresa Valentine
Last updated:  7/26/00