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A case study is performed to investigate the probable reasons behind substantial daytime sodium (Na) D1 airglow intensity (589.6 nm) variations measured using a ground-based monochromator during the three near consecutive days of February 2007 from Trivandrum (8.5°N, 77°E), India. The roles of both the resonance fluorescence and the chemistry have been considered in this study. It appears that fluorescence plays only a minor role towards the observed five to nine times of large intensity variations among these days. From investigations on the role of chemistry, it seems that through the Chapman chemical scheme, Na abundance contribute favorably, while the O3 concentrations and the ambient temperature do not play any role as such for the observed intensity variations. From further investigations, it transpires that because of pressure differences (approximately 0.0002 to 0.0003 hPa/day) in the emitting altitude region among these days, the variations in collisional quenching of excited NaO*(A2Σ+) (first excited electronic state of NaO that produces D line) contribute considerably towards the observed intensity variations. From consideration of all the possible factors, it appears that whereas resonance fluorescence plays only a minor role, chemistry has contributed to greater extent towards the observed significant intensity differences among these days.

Highly varying daytime sodium airglow emissions over an equatorial station: a case study based on the measurements using a grating monochromator