Cascade contributions to geocoronal Balmer α airglow line profiles are directly proportional to the Balmer β ∕α line ratio and can therefore be determined with near simultaneous Balmer β observations. Due to scattering differences for solar Lyman β and Lyman γ (responsible for the terrestrial Balmer α and Balmer β fluorescence, respectively), there is an expected trend for the cascade emission to become a smaller fraction of the Balmer α intensity at larger shadow altitudes. Near-coincident Balmer α and Balmer β data sets, obtained from the Wisconsin H alpha Mapper Fabry-Perot, are used to determine the cascade contribution to the Balmer α line profile and to show, for the first time, the Balmer β∕α line ratio, as a function of shadow altitude. We show that this result is in agreement with direct cascade determinations from Balmer α line profile fits obtained independently by high-resolution Fabry-Perot at Pine Bluff, WI. We also demonstrate with radiative transport forward modeling that a solar cycle influence on cascade is expected, and that the Balmer β ∕α line ratio poses a tight constraint on retrieved aeronomical parameters (such as hydrogen’s evaporative escape rate and exobase density).
Journal of Geophysical Research: Space Physics
American Geophysical Union
Grant or Award Name
NSF awards AGS 1347687, AGS 1352311, AST 1108911
Scholarly Commons Citation
Gardner, D. D., Mierkiewicz, E. J., Roesler, F. L., Nossal, S. M., & Haffner, L. M. (2017). Constraining Balmer alpha fine structure excitation measured in geocoronal hydrogen observations. Journal of Geophysical Research: Space Physics, 122, 10,727–10,747. https://doi.org/10.1002/2017JA024055