Abstract
Abstract. Rotational temperatures derived from the OH(8–3) band may vary by ~18K depending on the choice of transition probabilities. This is of concern when absolute temperatures or trends determined in combination with measurements of other hydroxyl bands are important. In this paper, measurements of the OH(8–3) temperature-insensitive Q/P and R/P line intensity ratios are used to select the most appropriate transition probabilities for use with this band. Aurora, airglow and solar and telluric absorption in the OH(8–3) band are also investigated. Water vapour absorption of P1(4), airglow or auroral contamination of P1(2) and solar absorption in the vicinity of P1(5) are concerns to be considered when deriving rotational temperatures from this band. A comparison is made of temperatures derived from OH(6–2) and OH(8–3) spectra collected alternately at Davis (69° S, 78° E) in 1990. An average difference of ~4K is found, with OH(8–3) temperatures being warmer, but a difference of this magnitude is within the two sigma uncertainty limit of the measurements. Key words. Atmospheric composition and structure airglow and aurora; pressure, density, and temperature)
Highlights
Warming of the troposphere due to increases in greenhouse gas concentrations is associated with enhanced cooling in the stratosphere and mesosphere (Berger and Dameris, 1993; Portman et al, 1995; Akmaev and Fomichev, 1998, 2000)
Temperature-independent intensity ratios are determined from the high-resolution spectra and compared with the ratios predicted by published transition probabilities to determine which transition probabilities are most appropriate to use when determining rotational temperatures in this band
Measurements of the OH(8–3) temperature-independent Q/P and R/P line ratios are generally consistent with LWR transition probabilities, and lower than Mies and T&L transition probabilities
Summary
1988) and can be used as a proxy for kinetic temperature at ∼87 km (She and Lowe, 1998). Differences in hydroxyl rotational temperatures derived from different bands have been interpreted as providing evidence for a height variation of hydroxyl upper state vibrational levels This is a possible source of hydroxyl temperature variability when different bands are measured. Temperature-independent intensity ratios are determined from the high-resolution spectra and compared with the ratios predicted by published transition probabilities to determine which transition probabilities are most appropriate to use when determining rotational temperatures in this band. Information gained from the high-resolution 1999 spectra is used to determine rotational temperatures from OH(8–3) spectra collected in 1990 These temperatures are compared with temperatures from alternately collected OH(6–2) spectra, derived using information on this band published by Greet et al (1998) and French et al (2000), to quantify differences which may influence temperature trends determined from combining measurements of these bands from different eras
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