Balmer alpha distributions over a solar cycle: Comparison of observations with theory

Abstract

Observations of Balmer α made since 1958 in the USSR, Norway, France, Bolivia, and the USA have been corrected for background effects and tropospheric scattering and are compared with radiative transfer calculations for exospheric temperatures ranging from 750° to 1500°K. The new calculations take into account the effects of hydrogen out to 70,000 km and are normalized to three times the Kockarts-Nicolet abundances, as required for consistency with Lyman α measurements. They show little change with exospheric temperature, in the relative brightness distributions with solar depression angle and azimuth with respect to the sun. The 56∶1 change in hydrogen density at 650 km for this temperature change with constant production rate results in about an eighteen-fold change in over-all brightness for a constant solar Lyman β flux. The observed change in brightness is by a factor of about 3 after correction for background effects and implies a six-fold change in flux at the line center of solar Lyman β. Measurements of the total solar Lyman β flux show a variation since 1961 that, when taken with a change in the self reversal, is consistent with the required line center solar Lyman β change. However, the absolute intensity of the line center flux is lower than required by a factor of 2 to 5.