  We investigate the solar modulation effect with the long time cosmic ray
proton and helium spectrum measured by AMS-02 on the time scale of a Bartels
rotation (27 days) between May 2011 and May 2017. The time-span covers the
negative heliospheric magnetic field polarity cycle, the polarity reversal
period and the positive polarity cycle. The unprecedented accuracy of AMS-02
observation data provide a good opportunity to improve the understanding of the
time dependent solar modulation effect. In this work, a two-dimensional solar
modulation model is used to compute the propagation of cosmic rays in the
heliosphere. Some important ingredients of the model which reflect the global
heliospherical environment are taken from the observations. The propagation
equation is numerically solved with the pubic Solarprop code. We find that the
drift effect is suppressed during the high solar activity period but nearly
recovered in the first half of 2017. The time-dependent rigidity dependence of
the mean free path is critical to reproduce the observations between August
2012 and October 2015.
