  Variations of the magnetic field within solar coronal mass ejections (CMEs)
in the heliosphere depend on the CME`s magnetic structure as it leaves the
solar corona and its subsequent evolution through interplanetary space. To
account for this evolution, we developed a new numerical model of the inner
heliosphere that simulates the propagation of a CME through a realistic
background solar wind and allows various CME magnetic topologies. To this end,
we incorporate the Gibson-Low CME model within our global MHD model of the
inner heliosphere, GAMERA-Helio. We apply the model to study the propagation of
the geoeffective CME that erupted on 3 April, 2010 with the aim to reproduce
the temporal variations of the magnetic field vector during the CME passage by
Earth. Parameters of the Gibson-Low CME are informed by STEREO white-light
observations near the Sun. The magnetic topology for this CME - the tethered
flux rope - is informed by in-situ magnetic field observations near Earth. We
performed two simulations testing different CME propagation directions. For an
in-ecliptic direction, the simulation shows a rotation of all three magnetic
field components within the CME, as seen at Earth, similar to that observed.
With a southward propagation direction, suggested by coronal imaging
observations, the modeled By and Bz components are consistent with the ACE
data, but the Bx component lacks the observed change from negative to positive.
In both cases, the model favors the East-West orientation of the CME flux rope,
consistent with the orientation previously inferred from the STEREO/HI
heliospheric images.
