Abstract
Abstract. Ground-based nightglow observations of the atomic oxygen green line at 557.7 nm have been carried out at a low latitude station Kolhapur (17° N), India, during November 2003–April 2004 and December 2004–May 2005. The nocturnal behaviour of OI 557.7 nm intensity and a comparative study with simultaneous OH Meinel band temperature measurements has been presented. OI 557.7 nm intensity and OH temperature variations covary on many occasions. It was found that an 8 h tide characterizes the variation of intensity and temperature on most nights, and especially during the month of January. This is the first report of prolonged measurements of OI 557.7 nm emission from India.
Highlights
In the lower thermosphere, the absorption of solar ultraviolet radiation in Schumann-Runge bands, Herzberg continuum and Lyman α line (121.5 nm) by molecular oxygen (O2) results in its photodissociation, leading to the formation of atomic oxygen (O)
According to Takahashi et al (1979), the mechanisms that contribute to the nocturnal variations of any emission feature from the upper mesosphere-lower thermosphere region are: firstly, a change in photochemical equilibrium, resulting in a change of mixing ratios of the atomic constituent involved; secondly, a variation in turbulence, resulting in enhancement of the eddy diffusion which in turn is responsible for the transport of minor species specially atomic oxygen; and thirdly, a change in the density of reacting species and the ambient temperature induced by the propagation of gravity waves and atmospheric tides
This report is the first to present the nocturnal behaviour of this emission feature over a prolonged period of time, spanning winter and spring during 2003–2005
Summary
The absorption of solar ultraviolet radiation in Schumann-Runge bands, Herzberg continuum (at wavelengths 140–200 nm) and Lyman α line (121.5 nm) by molecular oxygen (O2) results in its photodissociation, leading to the formation of atomic oxygen (O). This type of nocturnal variation is a widely observed feature, and has been explained in terms of the loss of atomic oxygen and absence of photolysis during the night (Takahashi et al, 1977) Sometimes such monotonous decreasing tendency was superseded by an increase in intensity during the dawn hours. According to Takahashi et al (1979), the mechanisms that contribute to the nocturnal variations of any emission feature from the upper mesosphere-lower thermosphere region are: firstly, a change in photochemical equilibrium, resulting in a change of mixing ratios of the atomic constituent involved; secondly, a variation in turbulence, resulting in enhancement of the eddy diffusion which in turn is responsible for the transport of minor species specially atomic oxygen; and thirdly, a change in the density of reacting species and the ambient temperature induced by the propagation of gravity waves and atmospheric tides.
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