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, lambda/sub D/, 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 Δtheta across the discontinuity, where Δtheta is of the order of lambda/sub D//lambda/sub i/, lambda/sub i/ being the ion inertial length. The polarization is left handed. These elementary pulse solutions exist only in a limited range of β/sub x/e and β/sub x/i values where β/sub x/e and β/sub x/i are the ratios of electron and ion pressure to magnetic pressure, the latter based on the magnetic field component B/sub x/, normal to the layer. The possibility that rotational discontinuities with a large angle change Δtheta 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