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Daytona Beach


Department of Physical Sciences

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Cascade contributions to geocoronal Balmer 𝛼 airglow line profiles are directly proportional to the Balmer π›½βˆ•π›Ό 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 theWisconsin 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 π›½βˆ•π›Ό 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 π›½βˆ•π›Ό line ratio poses a tight constraint on retrieved aeronomical parameters (such as hydrogen’s evaporative escape rate and exobase density).

Publication Title

Journal of Geophysical Research: Space Physics



American Geophysical Union

Available for download on Thursday, October 24, 2019