Abstract:
The diurnal variations in daytime airglow emission
intensity measurements at three wavelengths OI 777.4 nm,
OI 630.0 nm, and OI 557.7 nm made from a low-latitude location,
Hyderabad (17.5 N, 78.4 E; 8.9 N MLAT) in India
have been investigated. The intensity patterns showed
both symmetric and asymmetric behaviour in their respective
diurnal emission variability with respect to local noon.
The asymmetric diurnal behaviour is not expected considering
the photochemical nature of the production mechanisms.
The reason for this observed asymmetric diurnal behaviour
has been found to be predominantly the temporal variation
in the equatorial electrodynamics. The plasma that is transported
across latitudes due to the action of varying electric
field strengths over the magnetic equator in the daytime contributes
to the asymmetric diurnal behaviour in the neutral
daytime airglow emissions. Independent magnetic and radio
measurements support this finding. It is also noted that this
asymmetric diurnal behaviour in the neutral emission intensities
has a solar cycle dependence with a greater number of
days during high solar activity period showing asymmetric
diurnal behaviour compared to those during a low solar activity
epoch. These intensity variations over a long timescale
demonstrate that the daytime neutral optical emissions are
extremely sensitive to the changes in the eastward electric
field over low and equatorial latitudes.
