MHD modeling of a geoeffective interplanetary coronal mass ejection with the magnetic topology informed by in situ observations

Variations of the magnetic field within a solar coronal mass ejection (CME) in the heliosphere depend on the CME’s magnetic structure as it leaves the solar corona and its interplanetary evolution. 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 solar wind background 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 2010 April 3, aiming to reproduce the temporal variations of the magnetic field vector during the CME’s 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. However, the magnitudes of the components, particularly at the back of the CME, are underestimated by the model. With a southward direction, suggested by coronal imaging observations, the B x component lacks the observed change from negative to positive. In both cases, the model favors the east–west orientation of the flux rope, consistent with the orientation previously inferred from the images from STEREO/Heliospheric Imager.