Ion isotropy and fluctuations in the solar wind

The ion distribution in the solar wind is much more isotropic than would be expected on the basis of near conservation of magnetic moment, only weakly violated by particle collisions. It is generally thought that some instability must feed on the anisotropy and provide fluctuating fields which replace collisions to maintain near-isotropy. In this work, we consider the effects of measured fluctuations, with only general considerations as to their source. Data from Interplanetary Scintillations and fluctuations in plasma density have provided data on electric fields, while fluctuations in magnetic fields are measured directly. Data from URAP, the Unified Radio And Plasma experiment on Ulysses, will be used to fill in higher frequency ranges, to assess the variations in the fluctuations with time and space, and to help to identify wave modes. It is shown that electric field fluctuations are of the right order of magnitude to maintain ion isotropy.