OH-equivalent temperatures derived from ACE-FTS and SABER temperature profiles – a comparison with OH*(3-1) temperatures from Maynooth (53.2° N, 6.4° W)

Abstract

Abstract. OH-equivalent temperatures were derived from all of the temperature profiles retrieved in 2004 and 2005 by the ACE-FTS instrument in a 5 degree band of latitude centred on a ground-based observing station at Maynooth. A globally averaged OH volume emission rate (VER) profile obtained from WINDII data was employed as a weighting function to compute the equivalent temperatures. The annual cycle of temperature thus produced was compared with the annual cycle of temperatures recorded at the ground-based station more than a decade earlier from the OH*(3-1) Meinel band. Both data sets showed excellent agreement in the absolute value of the temperature minimum (∼162 K) and in its time of occurrence in the annual cycle at summer solstice. Away from mid-summer, however, the temperatures diverged and reach a maximum disagreement of more than 20 K in mid-winter. Comparison of the Maynooth ground-based data with the corresponding results from two nearby stations in the same time-period indicated that the Maynooth data are consistent with other ground stations. The temperature difference between the satellite and ground-based datasets in winter was reduced to 14-15 K by lowering the peak altitude of the weighting function to 84 km. An unrealistically low peak altitude would be required, however, to bring temperatures derived from the satellite into agreement with the ground-based data.OH equivalent temperatures derived from the SABER instrument using the same weighting function produced results that agreed well with ACE-FTS. When the OH 1.6 µm VER profile measured by SABER was used as the weighting function, the OH equivalent temperatures increased in winter as expected but the summer temperatures were reduced resulting in an approximately constant offset of 8.6±0.8 K Correspondence to: F. J. Mulligan (frank.mulligan@nuim.ie) between ground and satellite values with the ground values higher. Variability in both the altitude and width of the OH layer within a discernable seasonal variation were responsible for the changes introduced. The higher temperatures in winter were due to primarily to the lower altitude of the OH layer, while the colder summer temperatures were due to a thinner summer OH layer. We are not aware of previous reports of the effect of the layer width on ground-based temperatures.Comparison of OH-equivalent temperatures derived from ACE-FTS and SABER temperature profiles with OH*(3-1) temperatures from Wuppertal at 51.3 • N which were measured during the same period showed a similar pattern to the Maynooth data from a decade earlier, but the warm offset of the ground values was lower at 4.5±0.5 K. This discrepancy between temperatures derived from ground-based instruments recording hydroxyl spectra and satellite borne instruments has been observed by other observers. Further work will be required by both the satellite and ground-based communities to identify the exact cause of this difference.

Response of OH airglow temperatures to neutral air dynamics at 78°N, 16°E during the anomalous 2003–2004 winter

“…To make a realistic comparison, the kinetic temperatures have to be weighted over the OH emission layer to be equivalent to the ground‐based temperatures. Mulligan and Lowe [2008] present several methods to do this, and in this paper we calculate so‐called OH brightness temperatures using the OH 1.6 μ m volume emission rate (VER) measured simultaneously by SABER to weight the kinetic temperature profiles derived from measurements of CO 2 emissions made by SABER [ Mertens et al , 2004]. The OH 1.6 μ m VER signal covers the spectral interval 1.56–1.75 μ m and thus includes most of the Δ ν = 2 bands OH(4‐2) and OH(5‐3).…”

Revised molecular constants and term values for the X2Π and B2Σ+ states of OH

“…The Meinel system is useful in atmospheric science because the bands show evidence of gravity wave structure seen, for example, in all sky airglow images [10]. These airglow emissions are also used to derive rotational temperatures by taking appropriate ratios of line intensities and provide valuable information about the mesosphere [11]. The Meinel system can also be studied from orbit and the SABER emission radiometer instrument on the TIMED satellite is currently monitoring the OH airglow through two near infrared filters at 1.6 and 2 lm [12].…”

A comparison of ground-based hydroxyl airglow temperatures with SABER/TIMED measurements over 23° N, India

“…As hydroxyl emissions emanate from an extended altitude regime of ∼ 8-10 km width centred around 87 km (Baker et al, 2007;Nikoukar et al, 2007), an approach concerned with OH-equivalent temperature from the SABER kinetic temperature profiles was adopted by several investigators for fair comparison of ground-based and SABER measurements (Oberheide et al, 2006;López-González et al, 2007; Mulli- gan and Lowe, 2008;French and Mulligan, 2010). This concept is discussed in detail by French and Mulligan (2010).…”