Spacecraft measurements of propagating interplanetary shocks are often interpreted using the ideal magnetohydrodynamic (MHD) model of a planar shock wave travelling with constant velocity $\boldsymbol{V}_{\text{sh}}$ through a spatially uniform plasma. In particular, measurements of the plasma variables upstream and downstream have long been used in conjunction with the Rankine–Hugoniot conditions, also known as the MHD jump conditions, to determine shock velocities and other physical parameters of interplanetary shocks. This procedure is justified only if the shock velocity determined by the MHD jump conditions is unique. In this study the important property of uniqueness is demonstrated for non-perpendicular shocks in MHD media characterized by an isotropic pressure tensor. The primary conclusion is that the shock velocity is uniquely determined by the jump conditions regardless of the type of shock (slow, intermediate or fast). Several new formulas for the shock speed are also derived including one that is independent of the shock normal $\hat{\boldsymbol{n}}$. In principle, the solution technique developed here can be applied to estimate $\boldsymbol{V}_{\text{sh}}$ using solar wind data provided the measurements obey the MHD shock model with sufficient accuracy. That is not its intended purpose, however, and such applications are beyond the scope of this work.

The generation and propagation of a small-amplitude Langmuir pulse excited by a planar grid electrode in a spatially uniform collisionless plasma with a constant flow velocity is studied by solving the linearized Vlasov–Poisson equations. The electrode is transparent to the flow of particles, like a screen or a wire mesh. The particles are assumed to have a Kappa velocity distribution, a reasonable approximation for electron distribution functions in the solar wind. Exact, closed-form solutions are obtained for ${\it\kappa}=1$ , the Lorentzian distribution, and for ${\it\kappa}=2$ . The explicit form of the solution in the case ${\it\kappa}=2$ has not, to our knowledge, appeared in the literature before. The properties of the solutions are investigated and a practical technique for measuring the bulk flow velocity in plasma experiments is proposed that may be useful for high-accuracy, high-time-resolution measurements of the bulk flow velocity in the solar wind.