Abstract
OH airglow observed by the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) instrument on board the FORMOSAT 2 satellite is reported in this paper. The satellite is sun-synchronous and it returns to the same orbit at the same local time daily. By using this property, we can study the upper atmosphere in detail. With a CCD camera, ISUAL has measured the emission layers of OH Meinel band at 630 nm for several two-week periods in 2004 and 2007 in equatorial regions. ISUAL images are snapshots of the atmosphere 250 km (height) × 1200 km (horizontal distance). These images of OH airglow are analyzed to derive its peak height and latitudinal variations. ISUAL observation is unique in its capability of continuous observation of the upper atmosphere as the satellite travels from south to north along a specific orbit. However, 630 nm filter also measured O(1D) at 200 km, and there are interferences between O(1D) and OH airglows as as observed from a distance in space. We have studied the overlap of two airglows by simulations, and our final analyses show that OH airglow can be correctly derived with its average peak height of 89 ± 2.1 km usually lying within ±10° latitude about the equator. ISUAL data reveal detailed structures of equatorial OH airglow such as the existences of a few secondary maxima within the equatorial regions, and the oscillations of the peak latitudes. These results are discussed and compared with previous reports.
Highlights
In the upper atmosphere above 80 km, some layers of bright emissions are observable in the night
HRDI data showed OH airglow with an average peak height of 88 km (Yee et al 1997), and WINDII data show a peak height of 87 km (Zhang and Shepherd 1999)
Baker and Stair (1988) by various rocket flights found the peak height of OH airglow might vary between 82 and 99 km, depending on location, observation strategy, and OH vibrational state
Summary
In the upper atmosphere above 80 km, some layers of bright emissions are observable in the night. SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) on board TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite has been reported by Marsh et al (2006) and Baker et al (2007). Compared with ground based measurements, space measurements can provide data about the height and global distributions. Both HRDI and WINDII instruments have observed the equatorial enhancement resulting from tidal effects in the upper atmosphere (Yee et al 1997; Zhang et al 2001). SABER instrument has shown the equatorial enhancement of OH airglow and the effects of diurnal tides in the low latitudes (Marsh et al 2006)
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