Daily Variability in the Terrestrial UV Airglow

Abstract

New capability for observing conditions in the upper atmosphere comes with the implementation of global ultraviolet (UV) imaging from geosynchronous orbit. Observed by the NASA GOLD mission, the emissions of atomic oxygen (OI) and molecular nitrogen (N2) in the 133–168-nm range can be used to characterize the behavior of these major constituents of the thermosphere. Observations in the ultraviolet from the first 200 days of 2019 indicate that the oxygen emission at 135.6 nm varies much differently than the broader Lyman-Birge-Hopfield (LBH) emission of N2. This is determined from monitoring the average instrument response from two roughly 1000 km2 areas, well separated from one another, at the same time of each day. Variations in the GOLD response to UV emissions in the monitored regions are determined, both in absolute terms and relative to a running 7-day average of GOLD measurements. We find that variations in N2 emissions in the two separate regions are significantly correlated, while oxygen emissions, observed in the same fixed geographic regions at the same universal time each day, exhibit a much lower correlation, and exhibit no correlation with the N2 emissions in the same regions. This indicates that oxygen densities in the airglow-originating altitude range of 150–200 km vary independently from the variations in nitrogen, which are so well correlated across the dayside to suggest a direct connection to variation in solar extreme-UV flux. The relation of the atomic oxygen variations to solar and geomagnetic activity is also shown to be low, suggesting the existence of a regional source that modifies the production of atomic oxygen in the thermosphere.

Exploring Altitudinal Resolution of Twilight Airglow Red Lines Using Twilight Photometer

“…The research effort described by Thomas J. Immel et al. (2020); indicated that photoelectron populations stimulate emissions of N 2 are easily observed from space‐based platforms. The dissertation by Murray (2007) and recent work by Eastes (2000) focused on the N 2 Lyman‐Birge‐Hopfield (LBH) band (a1Πg − X1Σg+) emissions from the Earth's aurora and daytime airglow.…”

Special Issue Editorial: Atmospheric Airglow—Recent Advances in Observations, Experimentations, and Modeling

“…The recent (NASA) Global-scale Observations of the Limb and Disk (GOLD) mission provides a unique new view of the daytime thermosphere. Immel et al [1] studied the daily variability in the UV airglow (OI and N 2 in the 133-168-nm range) observed by the GOLD mission to characterize the behavior of these constituents of the thermosphere. Their results indicate that oxygen densities in the altitude range of 150-200 km vary independently from the variations in nitrogen.…”