Propagation of solar generated disturbances through the solar wind critical points: One-dimensional analysis

We investigate the proper method for mathematically simulating the formation of an interplanetary disturbance (IPD) in the subsonic, sub-Alfvénic region near the solar surface within the constraints of one-dimensional hydrodynamic and magnetohydrodynamic (MHD) analyses. We then numerically simulate the subsequent propagation of the IPD through the solar wind critical points in the equatorial plane to the outer corona. We show that, if the IPD is initiated outside the critical points, it always contains both a forward and reverse shock (a shock pair). This result contrasts with observations indicating that shock pairs at 1 AU which can be associated with solar events are rare occurrences in the solar wind. On the other hand, IPDs initiated inside the critical points contain only a forward shock at the leading edge. When the magnetic field is included in the simulation and the IPD is originated inside the critical points, the IPD contains a forward shock at its leading edge followed by large-amplitude, nonlinear, MHD waves which are convected outward by the solar wind. Unlike shock pairs, MHD waves are often observed in the solar wind. Hence, we conclude that physically realistic studies of the propagation of IPD which are assumed to originate near the solar surface must (1) initiate the IPD inside the critical points and (2) include the magnetic field. Although this conclusion is based on a one-dimensional analysis, we speculate that it would be equally valid in multi-dimensions.