Assuming that the coronal magnetic field can be approximated by a current-free extension of the photospheric field, the authors use spherical harmonic analysis and numerical simulations to study its rotational properties. In the outer corona, they find that the rotation rate is determined by three principal factors: 1. "Coronal filtering". 2. Global averages of the photospheric rotation rate. 3. Ongoing source eruptions. These principles allow to understand the observationally inferred rotational properties of the outer coronal field. The overall rigidity of the rotation profile reflects the tendency for the photosphere's non-axisymmetric flux to be concentrated toward lower latitudes, where the rotational shear is small; increased curvature and asymmetry occur during the rising phase of the sunspot cycle because of the presence of higher latitude flux. The coronal rotation rate shows a progressive acceleration due to the equatorward migration of sunspots.
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Wang et al. (1988) studied this question.