This proposal is for systematic studies of geocoronal Balmer-alpha line profiles to investigate the detailed behavior of cascade and other possible excitation mechanisms in addition to direct Lyman-beta excitation. For the first time coincident observation of geocoronal hydrogen Balmer-alpha and Balmer-beta line profiles will be made using two high resolution Fabry-Perot annular summing spectrometers located at the Pine Bluff Observatory near Madison, WI. The Balmer-alpha and Balmer-beta line profiles are composed of different fine structures, but are affected by the same exospheric kinematics. Comparison of both sets of observations with solar Lyman line radiative transfer modeling will facilitate isolation of signatures in the line profile due to kinematics from those due to cascade or other excitation mechanisms.
The potential for future coincident observations with instruments aboard the TIMED satellite could yield a very comprehensive body of consistently calibrated geocoronal Balmer-alpha, Balmer-beta, and Lyman-alpha emission data, along with their solar excitation fluxes, and lead to a new level of understanding of the physics of the hydrogen geocorona.
