Source Regions of the Slow Solar Wind

While the fast solar wind is generally thought to originate from coronal holes, the source of the slow solar wind is only known to be associated with the highly structured and highly variable streamer belt. There is growing evidence from multiple-station intensity scintillation measurements of solar wind velocity—often referred to as IPS for interplanetary scintillation—that the slow wind originates in localized regions of the solar corona overlying the streamer belt. In this paper, velocity structure in the corona is investigated based on estimates obtained from the power spectra of single-station intensity scintillation measurements. These measurements were conducted with the S- and X-band (13 and 3.6 cm wavelengths, respectively) radio signals of Voyager 2 during its superior conjunctions in 1979 and 1982. Unlike previous studies, simultaneous estimates of density fluctuation from the same intensity scintillation measurements were available to provide the coronal context for the velocity measurements. Solar eclipse pictures show that with increasing heliocentric distance, coronal streamers taper to narrow extensions or stalks of angular size 1–2° by a few solar radii. Prominent enhancements in density fluctuation characterizing such streamer stalks are found to coincide with the low speed wind measured by Voyager 2, leading to the first observational evidence for streamer stalks as the long sought coronal sources of the slow solar wind.