Signatures of thermospheric-exospheric coupling of hydrogen in observed seasonal trends of H α intensity

Observations were obtained at Pine Bluff Observatory, WI, from 2000 to 2001 using a high spectral resolution (R∼80,000) Fabry-Perot annular summing spectrometer. This dusk-to-dawn asymmetry in intensity is highest in winter months with a difference of ∼2.7 Rayleighs and smallest in summer months with a difference of ∼0.5 Rayleighs; observations near equinox show a dusk-to-dawn difference in intensity close to ∼1.3 Rayleighs.

Comparisons between modeled and observed dusk-to-dawn intensity variation show good agreement near the equinoxes. The modeled intensity was generated using the lyao_rt radiative transport code of Bishop (1999, doi-org.cuucar.idm.oclc.org/10.1016/S0022-4073(98)00031-4), employing NRLMSISE-00 thermospheric hydrogen profiles extended into the exosphere via the evaporative case of the Bishop analytic exosphere. Near the equinoxes and summer solstice, the model tends to agree with observations.