Size of the auroral oval: UV ovals and precipitation boundaries compared

K Kauristie*, J Weygand, T.I. Pulkkinen, JS Murphree, PT Newell

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review


The oval boundaries in 44 Viking UV images are compared with three critical boundaries as defined from simultaneous DMSP particle precipitation data. The particle boundaries are the equatorward boundary of the particle oval (often associated with the earthward edge of the main plasma sheet), the boundary between smooth and structured precipitation, and the poleward boundary of the particle oval (close to the open-closed field line separatrix). The UV oval is characterized by the latitude of maximum UV intensity, equatorward boundary, and poleward boundary which are the latitudes corresponding to the half values of the maximum intensity. Differences between the UV and particle boundaries are quantified in various magnetic local time sectors and at different activity levels. The study shows that the poleward boundary of the particle oval is often at greater than or equal to 2 degrees higher latitudes than the most intense UV luminosity. Large differences are typical especially in the midnight and morning sectors. The present results suggest that caution is needed in interpreting the dramatic poleward expansion of the oval in the UV images, or more generally in using UV images to compute changes in the amount of open flux under different states of substorm activity.

Original languageEnglish
Pages (from-to)2321-2331
Number of pages11
JournalJournal of Geophysical Research
Issue numberA2
Publication statusPublished - 1 Feb 1999
MoE publication typeA1 Journal article-refereed


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