Comparison of Single-Site Interplanetary Scintillation Solar Wind Speed Structure with Coronal Features
Interplanetary Scintillation (IPS) Observations were made during the period 1984 1990 using a single radio telescope at 103 MHz situated at Thaltej (Ahmedabad), India. Solar wind speeds were estimated using a recently developed method based on matching the observed IPS spectra with model solar wind spectra for Kolmogorov turbulence. The best-fit speeds derived are traced back to a source surface, and average velocity maps are made for each year, averaging over a number of Carrington rotations. It is found that the resulting single-site, large-scale IPS speed structure agrees well with that derived from 3-site observations from earlier workers. The IPS speed structure during this period was compared with other coronal features. Nearly 85% of the observed high-speed regions were associated with coronal holes. At solar minimum, in 1986, a quasi-sinusoidal, narrow belt of slow solar wind was observed which matched well with the neutral line structure of the solar magnetic field and the belt of active centers. Near solar maximum, in 1990, the speed structure was chaotic, similar to that of the neutral line, with low speed regions appearing all over the source surface.