A new class of forward‐reverse shock pairs in the solar wind

A new class of forward‐reverse shock pairs in the solar wind has been discovered using Ulysses observations at high heliographic latitudes. These shock pairs are produced by expansion of coronal mass ejections, CMEs, that have internal pressures that are higher than, and speeds that are comparable to, that of the surrounding solar wind plasma. Of six certain CMEs observed poleward of S31°, three have associated shock pairs of this nature. We suggest that high internal CME pressures may exist primarily for events that have high speeds close to the surface of the Sun.