Solar wind structure at 0.1-1 AU reconstructed from IPS observations using tomography

Although interplanetary scintillation (IPS) is a useful means to measure the solar wind in regions where spacecraft cannot access, the IPS measurement requires a line of sight integration to relate what is observed to a location in space. We have produced a Computer Assisted Tomography (CAT) program that optimizes a three-dimensional solar wind speed distribution to fit observed interplanetary scintillation data from STE Lab. Nagoya University. The program uses solar rotation and solar wind motion to provide 3-dimensional perspective views of each point in space accessible to the IPS observations and iterates to a least-square solution fit of the observations. We plot the optimized result as a Carrington map of solar wind speed at a height of 2.5 Rs and have confirmed (1) the solar wind near a solar minimum phase has a bimodal structure near the sun, that is, a low-speed region and a high-speed region are separated by a sharp speed gradient, (2) high-speed winds get their final speed of 750-800 km/s within 0.1 AU, and subsequently the evolution of solar wind structure is small at 0.1-1AU.