Evidence of ENA precipitation in the EUV dayglow

Abstract

Observations from the STP 78-1 satellite, at 600 km altitude, of the OI 989 and 1304 Å, and OII 834 Å dayglow emissions between March 20-29, 1979 show brightening at low and mid-latitudes (< 30° geomagnetic latitude) during enhanced geomagnetic activity, as determined by the Dst index. We attribute this increased dayglow, which varies by up to 20% from average quiet time emissions, to increased energetic neutral atom production in the ring current. These particles precipitate to lower altitudes where they collisionally excite ambient atmospheric and ionospheric oxygen, that manifest in enhanced airglow intensities. We present our results and the evidence from which we conclude we have detected the first evidence of extreme ultraviolet day-glow excited by low-latitude precipitation of energetic neutral atoms.