Kinematical properties of interplanetary coronal mass ejections detected by interplanetary scintillation observations during the solar cycle 23

We report kinematical properties of interplanetary coronal mass ejections (ICMEs) detected by interplanetary scintillation (IPS) observations. The IPS observations have been carried out since the early 1980s using the 327MHz radio-telescope system of the Solar-Terrestrial Environment Laboratory, Nagoya University. These observations allow us to probe into the solar wind between 0.2 and 1 AU with a cadence of 24 hours. In this study, we analyzed the data of solar wind disturbance factor (g-value) derived from IPS observations in 1997-2009 corresponding to the whole period of the solar cycle 23. From this analysis, we made a list of IPS disturbance event days (IDEDs) in the period. Further, we compare our list with that of near-Earth ICMEs compiled by Richardson and Cane [2010] with an assumption that an ICME cause an IDED. From this comparison, we identified 50 ICMEs, which are detected at three locations, i.e. near-Sun, interplanetary space, and near-Earth. Our statistical analyses for kinematical properties of these events yield following results: (1) fast ICMEs are rapidly decelerated, while slow ICMEs are accelerated, and consequently radial speeds converge on the speed of background solar wind during their outward propagation; (2) both of the accelerated and decelerated motions almost finish by 0.8AU with 490km/s of the critical speed for zero acceleration; (3) for the fast ICMEs, a_ave=k(V-V_bg) is more suited than a_ave=k(V-V_bg)|V-V_bg| to describes the relationship between average accelerations and speed differences, where a_ave, k, V, and V_bg are the average acceleration, coefficient, ICME speed, and speed of background solar wind, respectively. These results support a hypothesis that the radial motion of ICME is governed by drag force caused by an interaction with the background solar wind. Our results also suggest that stokes drag is a predominant force for the propagation of fast ICME.