Radial Distance Dependence of the Solar Wind Speed at High Latitudes Observed by Interplanetary Scintillation

Abstract

We have investigated the radial distance dependence of the solar wind speed during the years 1995 and 1996 using interplanetary scintillation (IPS) observations at the Solar-Terrestrial Environment Laboratory. We derived solar wind velocity distributions for regions inside and outside of 0.3 AU separately using a computerized tomography method to remove the biases involved in the line-of-sight integration measurements. The wind speeds at latitudes higher than 40°, which can be expected to be the fast wind regions in the solar activity minimum phase, are averaged for each of the inner and outer regions. Comparing the speeds of the outer and inner regions with Ulysses data, we found no significant differences, hence indicating that the high-speed solar wind is accelerated to its final speed by at least 20 solar radii (0.1 AU)