Abstract
Abstract. OH rotational temperatures have been observed at the Syowa Station, Antarctica (69° S, 39° E), which is located in the middle of the auroral zone and has a high-sensitivity spectrometer for the spectral region of the OH 8-4 band. A dataset of 153 nights was acquired during the 2008 austral winter season. Of the 153 nights, the weather and aurora conditions were only suitable on 6 nights to study the relationship between auroral activity and OH airglow variation. Of these 6 nights, a significant increase in the rotational temperature and a decrease in the intensity related to an aurora activity were identified on the night of 27/28 March 2008, but no such variations were seen during the other nights. The horizontal magnetic field disturbance on the night of 27/28 March was the largest of that winter, while the cosmic radio noise absorption was also very strong. These facts indicate that, compared with the other nights, a large flux of high-energy auroral particles precipitated during the night. It is suggested that the observed variations in the OH rotational temperature and airglow intensity were caused by a lowering of the average airglow height as a result of OH depletion in the upper part of the layer where high-energy auroral particles can reach.
Highlights
OH airglow, which was first discovered by Meinel (1950) as spectral line emissions followed by vibrational-rotational transitions, is one of the strongest emissions in the night sky
Since reliable atmospheric temperature of the mesopause region can be remotely derived from the spectrum of the OH airglow, many observations of OH airglow have been performed in observatories around the world using various spectrometers and imagers (Sivjee et al, 1972; Krassovsky, 1972)
The color image shown in the upper panel is a keogram of visible aurora along the magnetic meridian
Summary
1988) and more recently using satellites (Zhang and Shepherd, 1999; Liu and Shepherd, 2006), the mean altitude of the OH airglow layer has been measured to be 87 km, while the mean thickness has been measured to be 8 km. Harrison (1970) and Stubbs et al (1983) reported on the relationship between aurora and OH airglow. On the other hand, Stubbs et al (1983) showed a 40 K increase in the rotational temperature after an active auroral event. They compared rotational temperatures recorded before and after active auroral events whose interval was 4 h. Due the spectral overlap of the auroral and airglow emissions, it is difficult to study the relationship between aurora and OH airglow using optical methods. To study the relationship between the OH airglow and auroral activity, a fast spectrometer with a moderate spectral resolution is required. Given the equipment’s good spectral resolution and sensitivity, the OH rotational temperature can be derived every minute with an Published by Copernicus Publications on behalf of the European Geosciences Union
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