Sharp boundaries of the solar wind flows: Nonlinear mechanisms and structures

Strongly inhomogeneous flows with very sharp boundaries have been identified in the solar wind. Interpretation of these observations is based on two well-known nonlinear plasma effects. First, strong density irregularities of the flow can be generated at a certain distance from the source if there is modulation of the flow speed at the source level. Second, thus emerging inhomogeneities propagating in the plasma medium, experience a nonlinear profile distortion, which is expressed primarily in steepening of the leading edge of the propagating density concentration. On the small scale of the front, the picture is affected by superimposed kinetic effects which give rise to wave dispersion, and as a result determine the limiting small scale, on the order of the ion Larmor radius or ion inertial length.