  The energetic particle environment on the Martian surface is influenced by
solar and heliospheric modulation and changes in the local atmospheric pressure
(or column depth). The Radiation Assessment Detector (RAD) on board the Mars
Science Laboratory rover Curiosity on the surface of Mars has been measuring
this effect for over four Earth years (about two Martian years). The
anticorrelation between the recorded surface Galactic Cosmic Ray-induced dose
rates and pressure changes has been investigated by Rafkin et al. (2014) and
the long-term solar modulation has also been empirically analyzed and modeled
by Guo et al. (2015). This paper employs the newly updated HZETRN2015 code to
model the Martian atmospheric shielding effect on the accumulated dose rates
and the change of this effect under different solar modulation and atmospheric
conditions. The modeled results are compared with the most up-to-date (from 14
August 2012 to 29 June 2016) observations of the RAD instrument on the surface
of Mars. Both model and measurements agree reasonably well and show the
atmospheric shielding effect under weak solar modulation conditions and the
decline of this effect as solar modulation becomes stronger. This result is
important for better risk estimations of future human explorations to Mars
under different heliospheric and Martian atmospheric conditions.
