Extreme ultraviolet emissions for monitoring auroras in dark and daylight hemispheres

Abstract

Observations of auroral extreme ultraviolet (EUV) emissions from the noon‐midnight polar‐orbiting Space Test Program (STP) 78‐1 satellite are used to investigate the spectral features of the dayside auroral oval, nightside auroral oval, and the dayglow. The purpose of this study is to evaluate the possibility of using EUV atmospheric emissions for global auroral imaging and to study the temporal variations of the auroral EUV intensity with geomagnetic activity. It is found that during geomagnetically quiet times, O II 834Å, O I 989Å, and N2 1009 Å measurements can provide a clear distinction of the auroral oval above the dayglow background. During the very active period, five other EUV emissions can give good aurora‐to‐dayglow ratios. The auroral EUV emissions are more intense during magnetospheric substorms; however, we have not found a clear one‐to‐one relationship between them. It is also found that the auroral oval brightness, especially the noonside, increased during the initial phase of a geomagnetic storm. Thus, the sudden solar wind dynamic pressure enhancement is another important geophysical parameter that affects the EUV auroral emission.