Atomic Oxygen as the controlling factor in collocation of Elves and OH* Meinel band nightglow

Abstract:

The Imager of Sprite and Upper Atmospheric Lightning (ISUAL) onboard the Formosat-2 satellite has monitored Transient Luminous Events (TLEs) and lightning activity within the latitude interval +/- 60^o since May 2004. Channel 1 of the Imager with a bandpass from 623 to 754 nm is the channel usually used for recording TLEs. However, it also covers the wavelength range of the OH* Meinel Band nightglow (8,3) in the infrared region, and this circumstance opens a window for us to study the relationship between OH* nightglow and TLEs. The result shows that over 95% of the elves are within +/- 2 pixels in altitude of the brightest OH* emission. The abrupt increase of atomic oxygen with altitude serves to release electrons from O₂- thereby providing electrons the opportunity to attach to meteoric dust eventually. Atomic O is also vital to OH* nightglow as the necessary species to make O_3. Additionally , from the fundamental reaction , O+ O_{2^{- -> O3 + e-}} , it can be seen that this is not only a key process to move the free electrons to the ablation dust toward making the electron density ledge, but is also an effective way to make O₃ for the OH* nightglow. We suggest that the meteoric dust with abrupt appearance in the electron density ledge forms the upper boundary for the VLF waveguide. This circumstance may justify the use of the VLF waveguide cutoff height as a proxy for the dominant altitude of elves. When the global map of such cutoff heights (Toledo-Redondo et al., 2012) and the OH nightglow (WINDII) heights are compared, both show a distinct wavenumber-4 structure in the low-latitude region. The collocation of elves and the OH* nightglow layer is not coincidental and reveals new information about the structure of the D region.