Ground‐based observation of high‐altitude, high‐temperature emission in the O₂ atmospheric band nightglow

Abstract

[1] O 2 (b 1 AE g + À X 3 AE g À ) atmospheric band emission, when viewed from the ground outside the auroral zone, is considered to originate in the 90-100 km altitude region, from O-atom recombination. However, the v = 0,1 levels of the b 1 AE g + state can also be generated through an energy transfer process, when O( 1 D) collides with O 2 . In the absence of specific altitude information, as in ground-based measurements, the two sources can still be distinguished because of different characteristic temperatures. We have analyzed sky spectra from the Keck I and II telescopes on Mauna Kea, contrasting solar minimum and maximum conditions and variations with time of night. Utilizing the O 2 (b-X) 1-1 band, we find that in averaged solar minimum conditions, $75% of the emission comes from an altitude corresponding to 200 K, while $25% has a temperature near 700 K and therefore originates at high altitude. The fraction of high-temperature emission is often considerably greater early in the evening. At solar maximum, the high altitude component can be dramatically enhanced in the early evening; emission in the 1-1 band reaches intensitities of 100-150 R, with a rotational temperature near 1000 K. We also observe high-J b-X 0-0 band lines penetrating the Fraunhofer A-band region, the normal absorption becoming emission. Emission intensites deduced from such observations indicate that the ionospheric 0-0 band is at least as intense as the 1-1 band, as expected.

Review of tropical nightglow studies with astronomical instruments

“…Fig. 6 shows such an example in a sky spectrum from Keck/HIRES (Slanger et al, 2003a). In fact, the lower altitude emission is relatively unimportant here, and this can be demonstrated by noting that from the rotational distribution it is possible to determine a temperature for the emitting region.…”

O(1S → 1D,3P) branching ratio as measured in the terrestrial nightglow

“…A sky spectrum is the blank sky telluric spectrum that astronomers produce in the course of their measurements to subtract from their object spectrum. These spectra are taken at high resolution with echelle spectrographs and have wide wavelength coverage and thus are most desirable for simultaneous observations of features in different wavelength regions [Slanger and Copeland, 2003;Slanger et al, 2003a;Slanger et al, 2003b;Slanger et al, 2000a;Slanger et al, 2004b;Slanger and Osterbrock, 2000]. The accuracy of the wavelength calibrations has been demonstrated [Slanger et al, 2000b], and the spectra are calibrated in terms of intensity against standard stars.…”

Evidence for the lowering of the centroid of daytime thermospheric O(1D) 630.0nm emission over the magnetic equator: First results

“…Though the daytime observation of the O( 1 D) 630.0 nm was made first by Noxon and Goody as early as 1962, not many studies focused on this aspect in the later years (Noxon and Goody, 1962). However, a significant amount of work in this area of research has been done in India and over other latitudes during last two decade (Desai et al, 1979;Sivjee et al, 1980;Hernandez, 1982;Rees and Greenway, 1983;Narayanan et al, 1989;Biondi et al, 1995;Meriwether et al, 1986;Sridharan et al, 1991Sridharan et al, , 1994Sridharan et al, , 1998Sekar et al, 1993;Conde and Smith, 1997;Slanger et al, 2003;Zhang and Shepherd, 2004).…”