Wave transformation induced by shear flow in the magnetopause boundary layer

We study wave transformation induced by shear flow and energy exchange between the magnetohydrodynamic waves and mean flow in the magnetopause boundary layer (BL) with the non-modal approach. The magnetopause is assumed to be consisting of three BLs: the inner, outer layers and the transition region with uniform velocity shear and different plasma parameters. It is found that an initially-given Alfvenic perturbation experiences distinct changes in different regions. It is mainly transformed into the slow mode in the outer part of the magnetopause BL and fast mode in the inner part, while in the transition region both modes with comparative amplitudes can be obtained. We also find that the fluctuations with stronger fast mode oscillations can gain more energy from the background shear flow and get amplified as a result. The physical processes described above may be useful in understanding the anomalous transport phenomena of energy and momentum from the magnetosheath to the magnetosphere.