Global exospheric structure and temporal variability inferred from combined Lyman-alpha and Balmer-alpha emission data

Abstract:

Airglow emission from the terrestrial exosphere, which is generated through the resonant scattering or fluorescence of solar photons, is one of the best means available to infer exospheric properties, particularly the density of its major constituent, atomic hydrogen (H). Observations of both its ultraviolet emission at Lyman-alpha (121.6 nm) and its visible emission at Balmer-alpha (656.3 nm) have been acquired over several decades from numerous space and ground-based platforms, respectively. However, while each platform has yielded evidence for significant climatological and sporadic variability in observed radiances, few studies have investigated the nature and origins of correlations or discrepancies between these findings. In this presentation, we will compare and contrast historical observations of dayside exospheric emission acquired by NASA’s TIMED and TWINS missions with concident data acquired on the Earth’s nightside at several ground-based facilities. We will use this analysis to infer properties of global exospheric structure, particularly regarding the existence of a neutral geotail formation in the anti-solar direction, as well as differing responses to geomagnetic activity.