Cascade contributions to geocoronal Balmer � airglow line profiles are directly proportional to the Balmer �∕� line ratio and can therefore be determined with near simultaneous Balmer � observations. Due to scattering differences for solar Lyman � and Lyman � (responsible for the terrestrial Balmer � and Balmer � fluorescence, respectively), there is an expected trend for the cascade emission to become a smaller fraction of the Balmer � intensity at larger shadow altitudes. Near-coincident Balmer � and Balmer � data sets, obtained from theWisconsin H alpha Mapper Fabry-Perot, are used to determine the cascade contribution to the Balmer � line profile and to show, for the first time, the Balmer �∕� line ratio, as a function of shadow altitude. We show that this result is in agreement with direct cascade determinations from Balmer � 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 �∕� 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
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). https://doi.org/10.1002/2017JA024055
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