OH(6-2) spectra and rotational temperature measurements at Davis, Antarctica

Abstract

Abstract. The OH(6±2) band was monitored during 1990 at Davis, Antarctica 68X6 S, 78.0 E using a CzernyTurner scanning spectrometer. Spectra obtained with a 0.15-nm bandwidth and wavelength steps of 0.005 nm have been recorded in an attempt to isolate auroral features. This has enabled detailed study of weak features in the region k837X5À 855X5 nm. These weak features can contribute to the apparent intensity of Pbranch lines and to the background. Their presence is allowed for in our calculation of rotational temperature, but the P 1 3 line is excluded because of signi®cant contamination. An average temperature of 221 AE 2 K is obtained from a selected data set of 104 spectra. The mid-winter average temperature, for the months of May, June and July, is 224 AE 2 K, which is consistent with the 1986 CIRA model values for mid-winter at this height and latitude, but this result is dependent on the choice of transition probabilities. Preliminary assessments of seasonal and diurnal variations in rotational temperature and intensity are presented.

Mesospheric temperatures from observations of the hydroxyl (6–2) emission above Davis, Antarctica: A comparison of rotational and Doppler measurements

“…The Davis CTS has been operated for a number of years, and is described in detail by Greet et al (1998). A summary of the important features is given here.…”

“…The detector is a cooled GaAs photomultiplier. The spectral region near the P 1 branch has been extensively studied (Greet et al, 1998). Contamination from weak auroral lines, other OH emission features, and Fraunhoffer absorbtion lines have been identified and are allowed for or avoided in the spectra used here.…”

“…For derivation of temperatures, we used the method in Greet et al (1998). The measured P-branch intensities are used to calculate the ratio of molecules in the rotational levels of the upper vibrational state.…”

“…Turnbull and Lowe (1989) have shown the absolute temperature derived from a range of published transition probabilities increases as the ν (vibrational quantum number difference) of the band increases. For the OH(6-2) band, Greet et al (1998) calculate a range of 12 K for three sets of transition probabilities. French et al (2000) measured the temperature-independent line ratios of the OH(6-2) band and determined the fractions of the upper rotational states that decay via each branch, enabling rotational temperatures to be determined with an accuracy of 2 K. The average temperatures calculated for a selection of spectra using the experimentally derived ratios were within 2 K of the values obtained using the Langhoff et al (1986) transition probabilities (French et al, 2000).…”

“…A scanning Czerny-Turner spectrometer (CTS) recorded the Pbranch of the OH(6-2) band near λ840 nm; at the same time, the FPS observed the Q 1 (1) emission near λ834 nm on a number of nights in June 1999. Temperatures were derived from the CTS spectra using the method described in Greet et al (1998) and French et al (2000), while the approach of Greet (1997) was used for the FPS data.…”