Geocoronal Balmer-alpha line profile observations and forward-model analysis

High spectral resolution geocoronal Balmer-alpha line profile observations from Pine Bluff Observatory (PBO) are presented in the context of forward-model analysis. Here we explore using the radiative transfer code LYAO_RT of Bishop (1999, 2001), along with line intensity constraints of Bishop et al. (2004), to model line narrowing trends observed in the PBO dataset. A decrease in the Doppler width of the Balmer-alpha emission with shadow altitude is a persistent feature in every night of PBO observations in which a wide range of shadow altitudes are observed. Preliminary applications of the LYAO_RT code — which includes the ability to output Doppler line profiles for both the singly and multiply scattered contributions to the Balmer-alpha emission line — displays good qualitative agreement with regard to geocoronal Doppler width trends observed from PBO. Model-data Balmer-alpha Doppler width comparisons using the best-fit model parameters obtained during the March 2000 PBO/EURD forward-model study [Bishop et al., 2004] will be presented and discussed, including the feasibility of using Balmer-alpha observed Doppler widths as an additional model constraint in our forward-model search procedures to retrieve underlying hydrogen density distributions. This work is supported by National Science Foundation award AGS-2050077.