One year variations in the near Earth solar wind ion density and bulk flow velocity

One year periodic variations in the near Earth solar wind ion density and bulk flow velocity are reported. The variations show an inverse relationship between the ion velocity and density. The peak strength of the observed density variation ranges from 50-100% over the background. These variations imply either large scale mass loading inside the Earth's orbit or intrinsic solar modulations. Analyses of both near Earth and Pioneer Venus Orbiter spacecraft data provide a comparison at two different heliocentric distances. Several explanations for these variations are discussed