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auroral oval

A Dictionary of Astronomy | 1997 | 625 words | Copyright

auroral oval A high-latitude ring of more or less permanent aurora, girdling the geomagnetic pole at a distance of 2000–2500 km under quiet geomagnetic conditions. There are two ovals, one in either hemisphere, each the mirror-image of the other. They are displaced such that the dayside edge is closer to the pole than that on the night side. Under disturbed geomagnetic conditions, the auroral ovals brighten, broaden, and expand towards the equator, particularly on the night side, so the aurora becomes visible at lower latitudes. The auroral ovals remain relatively fixed in space above the rotating Earth.

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