Solar wind helium and hydrogen structure near the heliospheric current sheet: A signal of coronal streamers at 1 AU

We have investigated solar wind flow properties associated with very low helium to hydrogen abundance ratios ( A (He)) observed with Los Alamos instrumentation on IMP 6, 7, and 8 during the 1971 ‐ 1978 interval. A characteristic pattern has been discovered, consisting of correlated interplanetary field reversals, high plasma density, low and nearly identical H + and He ++ bulk velocities, low H + and He ++ kinetic temperatures and minimums in their ratio. A superposed epoch analysis of 74 well defined sector boundary crossings observed during the 1971–1978 interval provides impressive verification of the above correlation, featuring a pronounced minimum in A (He) at the sector boundary passage. Our epoch analysis provides the cleanest pattern of plasma characteristics yet found in the vicinity of the current sheet associated with sector boundaries. Because coronal streamers straddle the current sheet close to the sun, the pattern discovered is the ‘signal’ of a coronal streamer at 1 AU. Our results provide important constraints on models of helium dynamics in coronal streamers and the low speed solar wind.