Persistence of shocks to large distances in the solar wind

Present hydrodynamic models of solar wind streams predict that interactions will cause interplanetary shocks to decay and large‐scale structures to coalesce and smooth out, with a decay length of 10–15 AU for moderate or small‐amplitude shocks. The Pioneer 10 plasma data, extending 1–30 AU, are examined in the light of such predictions. It is found that coalescence of streams into a single stream per solar rotation does occur, in general, but that considerable structure remains by 30 AU. The leading edge of a stream often exhibits a velocity jump of >20 km/s; many of these may be shocks. There is a characteristic velocity‐density‐temperature signature of these distant streams which differs from the close‐in double‐shock signature. A unique transient was seen in July 1982, at 28 AU, with a velocity jump of about 235 km/s.