A statistical study of interplanetary shocks and pressure pulses internal to magnetic clouds

摘要

We have examined Wind field and plasma data over the time period from November of 1994 through August of 2003 to find cases of interplanetary shocks and pressure pulses internal to magnetic clouds for which we could determine accurate shock normal directions. We have found eight cases in 82 clouds, so these shocks and pressure pulses occurred in approximately 10% of the Wind magnetic clouds. Of the eight cases, six were forward shocks and two were pressure pulses. The internal shocks and pressure pulses tend to occur in the latter half of the clouds, i.e., timewise, about two-thirds of the way through. In every case the magnetic field change is highly compressive at the shock showing little or no change (<10°) in angle during or after the magnitude jump. These shocks and pressure pulses internal to magnetic clouds appear to be associated with outline asymmetric halo coronal mass ejections of greater than average speed which may imply an interaction between an earlier, slower halo CME and a later, faster, off-center CME driving a strong shock, but other interpretations are possible and they are discussed.