Electrostatic structure of the rotational discontinuity: The elementary pulse

An analysis is presented of the rotational discontinuity in a collision-free plasma when the width of the discontinuity is comparable to the Debye length, λD, so that a large deviation from charge neutrality occurs. It is found that such discontinuities have positive electrostatic potentials and structures similar to those of ion-acoustic solitons. The tangential magnetic field changes direction by a small angle Δθ across the discontinuity, where Δθ is of the order of λD/λi, λi being the ion inertial length. The polarization is left handed. These elementary pulse solutions exist only in a limited range of βxe and βxi values where βxe and βxi are the ratios of electron and ion pressure to magnetic pressure, the latter based on the magnetic field component Bx, normal to the layer. The possibility that rotational discontinuities with a large angle change Δθ are composed of wave trains of elementary pulses is discussed. Applications in the solar wind, at the magnetopause, and above the auroral zones are examined briefly.