The Far Ultraviolet Signatures of Conjugate Photoelectrons Seen by the Special Sensor Ultraviolet Spectrographic Imager

• Published in: Geophysical research letters Vol. 47; no. 1
• Main Authors: Kil, Hyosub, Schaefer, Robert K., Paxton, Larry J., Jee, Geonhwa
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.01.2020
• Subjects: Airglow; conjugate photoelectron; Conjugates; Defense programs; Distribution; DMSP satellites; Electron energy; Emission; Emission measurements; far ultraviolet emission; Far ultraviolet radiation; Latitude; Locations (working); Magnetic poles; Meteorological satellite program; Meteorological satellites; Morphology; Night; Oxygen; Photoelectrons; remote sensing; Satellites; Sensors; Signatures; Solstices; Special Sensor Ultraviolet Spectrographic Imager; Spectroscopy; thermosphere; Twilight glow; Winter
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL086383

This study investigates the origin of anomalous far ultraviolet emissions observed at night at the subauroral region by the Special Sensor Ultraviolet Spectrographic Imager on board the Defense Meteorological Satellite System‐F16 satellite. The global distribution of the anomalous emission is derived using the measurements of the oxygen atom 130.4‐nm emission in 2017. Our results show the extension of the anomalous emission from high latitudes to middle latitudes in the Northern American‐Atlantic sector during the December solstice and in the Southern Australia‐New Zealand sector during the June solstice. These observations indicate that the anomalous emission occurs in the winter hemisphere and is pronounced at locations close to the magnetic poles. The good agreement between the morphology of the anomalous emission and the predicted distribution of conjugate photoelectrons leads to the conclusion that the anomalous emissions are the signatures of conjugate photoelectrons. Plain Language Summary Conjugate photoelectrons are photoelectrons that originate from the magnetic conjugate locations in the sunlit hemisphere. Their existence is manifested by the observations of anomalous airglow and electron temperature enhancements at night. However, previous observations of conjugate photoelectrons were mostly confined to twilight at limited longitudes, and therefore, their global behavior has not yet been identified. This study derives the global morphology of conjugate photoelectrons using the measurements of far ultraviolet emissions by the Special Sensor Ultraviolet Spectrographic Imager on board the Defense Meteorological Satellite Program‐F16 satellite in 2017. Anomalous emissions of oxygen atom 130.4 nm are detected at night in the winter hemisphere preferentially at locations close to magnetic poles. These characteristics are consistent with the predicted distribution of conjugate photoelectrons. Our results demonstrate that far ultraviolet observations from space are valuable resources for the study of conjugate photoelectrons. Key Points Global morphology of conjugate photoelectrons is derived for the first time using the measurements of far ultraviolet emissions by SSUSI Anomalous oxygen atom 130.4 nm emissions appear at night in the winter hemisphere at the longitudes close to the magnetic poles Anomalous emission morphology is explained by the magnetic field configuration and solar zenith angle