The helium component of solar wind velocity streams

Systematic variations of the properties of the helium constituent of the solar wind in the velocity streams are described. It is found that the helium abundance na/np varies by about a factor of 2 as the stream is crossed. The velocity of the helium differs from that of the hydrogen by a few kilometers per second throughout much of the stream structure. This velocity difference is greatest immediately after the proton density peak passes, the helium velocity being typically 20 km/s faster than the protons at that position in the stream. A sharp dip in the relative temperature Tα/Tp is centered on the proton density peak. Although it appears reasonable that at least the velocity and temperature effects are due to the dynamic interactions of the two streams, it is not yet clear exactly what physical processes are directly involved in producing the effects described here.