Hydrodynamic theory of drift Kelvin-Helmholtz instabilities

The hydrodynamic theory of drift Kelvin-Helmholtz instabilities is discussed. It is shown that the hydrodynamic approach gives, in the region of its applicability, the same results as the kinetic one. Previous studies on the hydrodynamic theory of drift Kelvin-Helmholtz instabilities are analysed. It is shown that certain parts of these studies are incorrect. Reasons for this are discussed.