Auroral Oval and Polar Substorms Observed by a Satellite and Ground-Based Observations in Antarctica

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The morphology of the "discrete" and "diffuse" auroral belts in the southern polar region is statistically examined as a function of geomagnetic Kp-index, using USAF-DAPP auroral photographs. Results of the statistical analyses are summarized in Fig. 9,which indicates the following characteristics of the two auroral belts. (a) The discrete auroral belt is always located on the poleward side of the diffuse auroral one. (b) The discrete auroras are observed mostly in the evening-to-midnight sectors, whereas the diffuse auroras are dominant in the midnight-to-early morning sectors. (c) The discrete auroras are observable in the evening sector even when Kp-index is very low; the discrete auroral belt in such a case is identified to the so-called auroral oval. (d) The discrete auroral belt approaches to a circular shape along 71°-72° in geomagnetic latitude when Kp-index approaches Kp≧5. (e) The diffuse auroral belt is confined to the night-side sectors during the geomagnetically quiet period, but it expands towards the evening sector along a geomagnetic latitude circle of 68°-69°, accompanied by a rapid expansion of width, in association with increasing Kp-index. Comparisons of DAPP auroral photographs and all-sky camera ones with scanning auroral spectrophotometric data on ground for H_β 4861 Å and OI 5577 Å emission lines have identified the discrete and diffuse auroral belts to the electron and proton auroral belts respectively.
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Auroral Oval and Polar Substorms Observed by a Satellite and Ground-Based Observations in Antarctica

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