  In this paper, ten CME events viewed by the STEREO twin spacecraft are
analyzed to study the deflections of CMEs during their propagation in the
corona. Based on the three-dimensional information of the CMEs derived by the
graduated cylindrical shell (GCS) model [Thernisien et al., 2006], it is found
that the propagation directions of eight CMEs had changed. By applying the
theoretical method proposed by Shen et al. [2011] to all the CMEs, we found
that the deflections are consistent, in strength and direction, with the
gradient of the magnetic energy density. There is a positive correlation
between the deflection rate and the strength of the magnetic energy density
gradient and a weak anti-correlation between the deflection rate and the CME
speed. Our results suggest that the deflections of CMEs are mainly controlled
by the background magnetic field and can be quantitatively described by the
magnetic energy density gradient (MEDG) model.
