Boundary-Driven Kelvin-Helmholtz Waves in a Space Magnetized Plasma

Kelvin‐Helmholtz instability (KHI) is a shear flow-driven instability that imposes important changes in the macroscopic dynamics of some magnetized plasmas such as the solar corona, astrophysical jets, and Earth's magnetopause. Using two-dimensional magnetohydrodynamic (MHD) simulations, the externally driven KHI is studied in a compressible plasma with a uniform magnetic field parallel to the direction of flow streaming. We show that the perpendicular perturbation of either plasma velocity or magnetic field on the fluid boundary in the form of a single localized pulse or a sinusoidal wave or a superposition of multiple sinusoidal waves with random wavelengths and amplitudes results in the excitation and the fast growth of KHI on the interface layer. It is found that as the wavelength of sinusoidal perturbation is smaller or the amplitude is larger, the KHI becomes faster. However, in the fully nonlinear regime, the dynamics of KHI becomes independent of the type or the magnitude of boundary perturbation. Moreover, it is shown that when the boundary is disturbed by a single highly localized pulse of plasma velocity, the formation location of KH vortices on the interface layer is irregular. The KHI will then develop throughout the interface layer. The externally forced KHI is more effective in space and astrophysical plasmas when the internal perturbations are absent or very weak on the interface layer or the initially weak shear flow is unable to trigger the KHI sufficiently. In these environments, the boundaries are highly likely to be disturbed continuously or intermittently by external fluid motions.