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On the Cause of the Post‐Sunset Nocturnal OI 630 nm Airglow Enhancement Over Low‐Latitude Thermosphere
Author(s) -
Saha Sovan,
Pallamraju Duggirala,
Pant Tarun K.,
Chakrabarti Supriya
Publication year - 2021
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2021ja029146
Subject(s) - airglow , sunset , thermosphere , nocturnal , atmospheric sciences , altitude (triangle) , earth's magnetic field , environmental science , daytime , latitude , low latitude , local time , atmosphere (unit) , ionosphere , zonal and meridional , climatology , geology , meteorology , physics , geodesy , astronomy , geophysics , mathematics , statistics , geometry , magnetic field , quantum mechanics
Airglow emissions serve as good tracers of the altitudinal regions at which they originate. OI 630 nm (red line) nocturnal emissions originate from around 250 km altitude. A total of 142 nights of data corresponding to the months of January, February, and March in the years 2013, 2014, and 2016, obtained from Mt. Abu (24.6°N, 72.7°E, 16°N Mag), Gurushikhar, India, a low‐latitude location, are investigated. These are compared with the column integrated emission rates calculated using, as inputs, the measured electron density profiles obtained from a digisonde from Ahmedabad (AMD, 23.0°N, 72.6°E, 15°N Mag), India. Following the expected monotonic decrement in the emissions after sunset, an enhancement is observed on several nights that peaks at around 20–21 local time (LT). The cause for this enhancement has been investigated in detail and it is found that the neutral winds, as obtained using digisondes at two locations, show almost a very good correlation between a poleward directed wind or cessation of equatorward wind over AMD and the observed airglow emission enhancement in the post‐sunset time. Further, the percentage enhancement in emissions also shows a decrease in magnitudes from January to March which has a broad similarity to the decrease in the model climatological meridional wind magnitudes in the same duration. Based on the data spanning over different years, it is inferred that, during geomagnetic quiet periods, almost all of the nocturnal variability in OI 630 nm emissions is due to the variations in the neutral wind.