  Recent studies of interstellar neutral (ISN) hydrogen observed by the
Interstellar Boundary Explorer (IBEX) suggested that the present understanding
of the radiation pressure acting on hydrogen atoms in the heliosphere should be
revised. There is a significant discrepancy between theoretical predictions of
the ISN H signal using the currently used model of the solar Lyman-alpha
profile by Tarnopolski et al. 2009 (TB09) and the signal due to ISN H observed
by IBEX-Lo. We developed a new model of evolution of the solar Lyman-alpha
profile that takes into account all available observations of the full-disk
solar Lyman-alpha profiles from SUMER/SOHO, provided by Lemaire et al. 2015
(L15), covering practically the entire 23rd solar cycle. The model has three
components that reproduce different features of the profile. The main shape of
the emission line that is produced in the chromosphere is modeled by the kappa
function; the central reversal due to absorption in the transition region is
modeled by the Gauss function; the spectral background is represented by the
linear function. The coefficients of all those components are linear functions
of the line-integrated full-disk Lyman-alpha irradiance, which is the only free
parameter of the model. The new model features potentially important
differences in comparison with the model by TB09, which was based on a limited
set of observations. This change in the understanding of radiation pressure,
especially during low solar activity, may significantly affect the interstellar
H and D distributions in the inner heliosphere and their derivative
populations.
