Analysis of previously reported observations of the solar wind‐barium interaction associated with the AMPTE artificial cornet release of December 27, 1984, is presented. On the basis of these results we argue that the solar wind couples momentum (and energy) to the barium ions through both laminar and turbulent processes. The laminar forces acting on the particles are the laminar electric and magnetic fields; the turbulent forces are associated with the intense electrostatic wave activity. This wave activity is shown to be caused by a cross‐field solar wind proton‐barium ion streaming instability. The observed wave frequencies and saturated amplitudes are consistent with our theoretical ana