On the Acceleration of the Solar Wind: Role of the Inhomogeneous Flow

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Abstract
It is shown that an inhomogeneous flow is capable of converting Alfvén waves escaping from the solar atmosphere into other types of MHD waves that can be efficiently dissipated. The efficiency of this process depends on local characteristics of the medium. Using the geometry of the solar wind, it is shown how this mechanism operates in different regions of the solar wind and what the preferred way of the coupling process is in those regions. It is suggested that mode conversion induced by inhomogeneous flow, particularly by shear velocity flow, could be the basic mechanism required for the solar wind acceleration in the coronal holes. It is shown that this mechanism is most efficient in the fast-expanding regions of polar coronal holes and how it contributes to the detected long-period Alfvén waves and density fluctuations in the solar wind. The results demonstrated by numerical simulations coincide with observations.