Analysis of Balmer alpha intensity measurements near solar minimum

Balmer a intensity measurements made with a dual etalon Fabry-Perot spectro meter at Haleakala during two campaigns in 1988 are presented. The data fro m each campaign demonstrate night-to-night stability, despite variations in geophysical conditions. Analysis of these data using a nonisothermal Lyman beta radiative transport code, updated solar Lyman beta line-center flux e stimates, and corrected thermospheric atomic hydrogen density profiles poin ts to the resolution of the "factor of 2" problem. A careful reassessment o f other mechanisms for upper atmospheric Balmer a excitation has also been carried out. (C) 2001 Elsevier Science Ltd. All rights reserved.