Comparison of VLT/X-shooter OH and O2 rotational temperatures with consideration of TIMED/SABER emission and temperature profiles

Autor(en)

Stefan Noll, Wolfgang Kausch, Stefan Kimeswenger, Stefanie Unterguggenberger, Alan M. Jones

Abstrakt

Rotational temperatures Trot derived from lines of the same OH band are an important method to study the dynamics and long-term trends in the mesopause region near 87 km. To measure realistic temperatures, a corresponding Boltzmann distribution of the rotational level populations has to be achieved. However, this might not be fulfilled, especially at high emission altitudes. In order to quantify possible non-local thermodynamic equilibrium (non-LTE) contributions to the OH Trot as a function of the upper vibrational level v', we studied a sample of 343 echelle spectra taken with the X-shooter spectrograph at the Very Large Telescope at Cerro Paranal in Chile. These data allowed us to analyse 25 OH bands in each spectrum. Moreover, we could measure lines of O2b(0-1), which peaks at about 94 to 95 km, and O2a(0-0) with an emission peak at about 90 km. The latter altitude is reached in the second half of the night after a rise of several km because of the decay of a daytime population of excited O2. Since the radiative lifetimes for the upper levels of the two O2 bands are relatively long, the derived Trot are not significantly affected by non-LTE contributions. These bands are well suited for a comparison with OH if the differences in the emission profiles are corrected. For different sample averages, we made these corrections by using OH emission, O2a(0-0) emission, and CO2-based temperature profile data from the multi-channel radiometer SABER on the TIMED satellite. The procedure relies on differences of profile-weighted SABER temperatures. For an O2a(0-0)-based reference profile at 90 km, we found a good agreement of the O2 with the SABER-related temperatures, whereas the OH temperatures, especially for the high and even v', showed significant excesses with a maximum of more than 10 K for v' = 8. The exact value depends on the selected lines and molecular parameters. We could also find a nocturnal trend towards higher non-LTE effects, particularly for high v'. The amplitude of these variations can be about 2 K or less, which tends to be significantly smaller than the total amount of the non-LTE contributions. The found variations can be critical for dynamical studies based on Trot derived from OH bands with high v'.

Organisation(en)

Institut für Astrophysik

Externe Organisation(en)

Leopold-Franzens-Universität Innsbruck, Max-Planck-Institut für Astrophysik

Journal

Atmospheric Chemistry and Physics Discussions

Band

15

Seiten

30793 - 30856

Anzahl der Seiten

64

DOI

https://doi.org/10.5194/acpd-15-30793-2015

Publikationsdatum

11-2015

Peer-reviewed

Ja

ÖFOS 2012

103003 Astronomie, 103004 Astrophysik

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/comparison-of-vltxshooter-oh-and-o2-rotational-temperatures-with-consideration-of-timedsaber-emission-and-temperature-profiles(aab03686-a98d-4cda-92cf-50212cb763d7).html