Evidence for a structure-free state at high solar wind speeds

A statistical study has been made of the variability of the basic solar wind flow parameters in high- and low-speed flows. Care was taken to exclude data taken during positive speed gradients, where dynamical effects severely alter the flow parameters. The study reveals that other than the bulk velocity the flow parameters within high-speed streams are steadier and more uniform from stream to stream than they are within low-speed flows, by a factor of 3. Comparison of simple models of the structure-free solar wind with average high-speed flow parameters should therefore be more meaningful than comparison with low-speed parameters. Of particuar importance to models of the lower corona and chromosphere-corona transition region are the particle and energy fluxes carried by the solar wind. If we assume that all of the solar wind originates in coronal holes, our best estimates of these fluxes at 1 R/sub s/ are 1.2 x 1014 cm-2 s-1 and 6.4 x 105 ergs cm-2 s-1, respectively, with an uncertainty of +- 40%. Interestingly, the He abundance is observed to be nearly uniform with high-speed flows at 1 AU. Thus it seems unlikely that a steady state fractionation of heavy elements occurs in those open field regions of the low corona from which the high-speed solar wind originates. The high-speed solar wind He abundance may therefore be a faithful measure of the He abundance of the outer layer of the sun. Our best estimate is N/sub a//N/sub p/=0.048 +- 0.005, where N/sub a/ and N/sub p/ are the densities of the alpha particle and proton populations, respectively