Noncompressive density enhancements in the solar wind


  • J. T. Gosling,

  • E. Hildner,

  • J. R. Asbridge,

  • S. J. Bame,

  • W. C. Feldman


High densities are sometimes observed in the solar wind when the bulk flow speed is nearly constant or falling. In contrast to the large density compressions observed on the rising speed portions of high-speed streams, these high densities do not appear to be generated in interplanetary space. Typically, the magnetic field is not enhanced within these events, and the proton and/or electron temperatures are low and vary in opposition to the density. Approximately ⅓ of these density events contain interplanetary magnetic field reversals, although these reversals are often ‘noisy’ and usually do not qualify as sector boundaries. We estimate by assuming an areal extent that the average event contains approximately 1016 g of material and 2.6 × 1031 ergs so that the aggregated events, when they are common, make a nonnegligible contribution to the total mass and energy budget of the solar wind at 1 AU. Values of the frequency of occurrence, duration, mass, energy, and speed of these density enhancements are comparable to those of solar coronal mass ejection events, suggesting a direct but as yet unproved association between these phenomena.