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

Abstract

A case study is performed to investigate the probable reasons behind substantial daytime sodium (Na) D 1 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 O 3 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 * (A 2 Σ + ) (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.

Dependence of mesospheric Na and Fe distributions on electron density at Arecibo

“…Such temperature fluctuations can influence the mesospheric chemistry, which can affect the strength of sporadic neutral layers as a result of ion-neutral coupling. The Na dayglow intensity variations observed for a few days from Trivandrum (India), a lowlatitude station, have been attributed to chemistry (Hossain et al, 2014). Another factor mentioned previously that can affect the strength of neutral sporadic activity can be due to inhomogeneity in the medium or advection, but that alone cannot explain why the minor species like Na show stronger sporadic layer as compared to one of the major metals like Fe relative to their main or permanent layers.…”

Modeling of Na airglow emission and first results on the nocturnal variation at midlatitude

“…There are a very limited number of studies which have been reported in the literature on VER of sodium D line airglow emission [Clemesha et al, 1995;Hecht et al, 2000;Sarkhel et al, 2010;Plane et al, 2012;Hossain et al, 2014]. Most of the VER profiles have been derived from either rocket measurement intensity or ground-based airglow intensity.…”

“…The ablation of meteors at the mesopause region results in the formation of the sodium layer [Plane, 1991]. Due to the fact that it has a large scattering cross section and also that it acts as a tracer for the thermal and dynamical states of the atmosphere in this altitude range [Plane et al, 1999;Griffins et al, 2001], the mesospheric sodium has been studied extensively among all meteoric metals [Kirchhoff et al, 1981;Kirchhoff , 1986;Plane, 1991;Clemesha et al, 1995;Hecht et al, 2000;Plane et al, 1999;Griffins et al, 2001;Slanger et al, 2005;Fan et al, 2007;Clemesha et al, 2010;Plane et al, 2012;Hossain et al, 2014]. The peak density layer exists at around 90 km.…”