Solar wind density structure at 1 AU and comparison to Doppler scintillation measurements

Results of a survey of solar wind density fluctuations in different flow types observed by ISEE-3 at I AU are presented and compared with Doppler scintillation measurements. We consider coronal hole, plasma sheet, interstream, CME and sheath interaction region Bow types. For the quasi-stationary solar wind, densities (N) and density fluctuation levels (Delta N) are low in coronal hole Bow, and high in the plasma sheet containing the heliospheric current sheet (HCS). The highest fluctuation levels are found in the sheath compression regions between CMEs and associated forward shocks. The streamer structure around the HCS broadens and erodes with distance from the Sun, and the broadened Doppler scintillation signature at I AU is in good qualitative agreement with ISEES superposed epoch analysis. The observed asymmetry about the HCS is an expected result of solar wind dynamic evolution. A greater contrast between flow types is seen in Delta N levels rather than in N itself. Doppler scintillation responds to Delta N and thus provides a sensitive means of detecting interplanetary disturbances. However, we find that Delta N/N is not constant in the solar wind, and thus enhanced scintillation cannot unambiguously imply enhanced density.