Tracking heliospheric disturbances by interplanetary scintillation

Coronal mass ejections are known as a solar cause of significant geospace disturbances, and a fuller elucidation of their physical properties and propagation dynamics is needed for space weather predictions. The scintillation of cosmic radio sources caused by turbulence in the solar wind (interplanetary scintillation; IPS) serves as an effective ground-based method for monitoring disturbances in the heliosphere. We studied global properties of transient solar wind streams driven by CMEs using 327-MHz IPS observations of the Solar-Terrestrial Environment Laboratory (STEL) of Nagoya University. In this study, we reconstructed three-dimensional features of the interplanetary (IP) counterpart of the CME from the IPS data by applying the model fitting technique. As a result, loop-shaped density enhancements were deduced for some CME events, whereas shellshaped high-density regions were observed for the other events. In addition, CME speeds were found to evolve significantly during the propagation between the corona and 1 AU.