Browsing by Author "Frey, Harald U."
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- Daily Variability in the Terrestrial UV AirglowImmel, Thomas J.; Eastes, Richard W.; McClintock, William E.; Mende, Steven B.; Frey, Harald U.; Triplett, Colin C.; England, Scott L. (MDPI, 2020-09-30)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.
- Reducing the Ionospheric Contamination Effects on the Column O/N-2 Ratio and Its Application to the Identification of Non-Migrating TidesKrier, Christopher S.; England, Scott L.; Meier, R. R.; Frey, Harald U. (American Geophysical Union, 2023-04)Prior investigations have attempted to characterize the longitudinal variability of the column number density ratio of atomic oxygen to molecular nitrogen (SO/N-2) in the context of non-migrating tides. The retrieval of thermospheric SO/N-2 from far ultra-violet (FUV) emissions assumes production is due to photoelectron impact excitation on O and N-2. Consequently, efforts to characterize the tidal variability in SO/N-2 have been limited by ionospheric contamination from O+ + e radiative recombination at afternoon local times (LT) around the equatorial ionization anomaly. The retrieval of SO/N-2 from FUV observations by the Ionospheric Connection Explorer (ICON) provides an opportunity to address this limitation. In this work, we derive modified SO/N-2 datasets to delineate the response of thermospheric composition to non-migrating tides as a function of LT in the absence of ionospheric contamination. We assess estimates of the ionospheric contribution to 135.6 nm emission intensities based on either Global Ionospheric Specification (GIS) electron density, International Reference Ionosphere (IRI) model output, or observations from the Extreme Ultra-Violet imager (EUV) onboard ICON during March and September equinox conditions in 2020. Our approach accounts for any biases between the ionospheric and airglow datasets. We found that the ICON-FUV data set, corrected for ionospheric contamination based on GIS, uncovered a previously obscured diurnal eastward wavenumber 2 tide in a longitudinal wavenumber 3 pattern at March equinox in 2020. This finding demonstrates not only the necessity of correcting for ionospheric contamination of the FUV signals but also the utility of using GIS for the correction.