Evidence for local ion heating in solar wind high speed streams

The thermal anisotropies near the peaks of proton distributions are observed to vary characteristically across two simple high speed streams. Before the time of maximum velocity gradient T∥ of the core distribution is greater than T⊥ but afterwards, and persisting throughout the remainder of the high speed region, T∥ < T⊥. This implies that it may not be necessary to invoke extended ion heating close to the sun to explain enhanced ion temperatures associated with high speed streams and that the T‐V relation may be primarily the result of local heating near 1 AU.