Study of variation of propagation velocity of solar wind disturbance

*Masahiro Yamashita[1] ,Munetoshi Tokumaru [1]
Masayoshi kojima [1],P.K. Manoharan [2]
Solar-Terrestrial Environment Laboratory, Nagoya University[1]
Radio Astronomy Centre, Tata Institute of Fundamental Research, India[2]

In this study, we reconstructed the CME's 3-D structure from g-value obtained from IPS observations at Solar-Terrestrial Environment Lab. and Ooty Radio Telescope. We made the calculation of los integration of the g-value by assuming the shell-shape CME model which is given by six free parameters, and determined the most suitable set of those parameters for IPS observations. Then, we determined the propagation speed by comparing with coronagraph data, radio observations, and in situ data. As result, the propagation speed of interplanetary CME is found to decelerate within increasing radial distance. We consider that this deceleration of the propagation speed may depend on the condition of ambient solar wind.

Interplanetary scintillation (IPS) measurements are an effective method to study the physical properties of solar wind disturbances in the inner heliosphere. In particular, all-sky map of solar wind density disturbance factor, so-called "g-value", which is derived from IPS measurements are useful to clarify the three-dimensional structure and propagation of the coronal mass ejection (CME) in the interplanetary space. All-sky maps of g-value have been obtained regularly from IPS measurements at 327 MHz with the IPS system of the Solar-Terrestrial Environment Lab.(STEL), Nagoya Univ., and Ooty Radio Telescope (ORT), India. However, observed g-value data are biased by the line-of-sight (los) integration, and it is difficult to analyze the property of interplanetary CME from observed g-value data directly. To remove the los integration effect, we made here the calculation of los integration of the g-value by assuming the shell-shape CME model which is determined by six parameters (i.e. distance from the sun, longitude and latitude of the central position, the radial thickness, the half cone angle, the local enhancement factor). We determined the most suitable set of those parameters by matching g-values obtained from the model calculations to those from IPS observations by STEL and ORT. Then, we determined the propagation speed by comparing coronagraph data, radio observations, and in situ data. In this time, we analyzed events observed during 1997 to 2000. As result, the propagation speed of interplanetary CME is found to decelerate as radial distance increase. We consider that this deceleration of the propagation speed may depend on the condition of ambient solar wind.