Influence of the Solar Wind Speed on the Propagation of Coronal Mass Ejections

Abstract:

We investigate the influence of the solar wind (SW) on the propagation of a set of 191 coronal mass ejections (CMEs) near the Sun during the period 1996-2013. The CMEs were observed by LASCO on board SOHO and their source regions were identified using the CME-associated eruptive features (flares, filament eruptions, dimmings) in X-ray, EUV, microwave, and Hα observations. The SW speeds above the CME source regions were estimated from the interplanetary scintillation (IPS) observations from the Solar Terrestrial Environ Laboratory, Nagoya University. We considered only CMEs from close to the limb in order to avoid the projection effects. We also considered CMEs with at least 10 height-time measurements in order to avoid the large uncertainty in the acceleration measurements. We confirm the well-known CME-SW relationship that the CMEs propagating faster (slower) than the ambient solar wind are likely to decelerate (accelerate). The correlation between the acceleration and the difference of the CME and the SW speeds is high with a correlation coefficient of -0.74, slightly lower compared to the one for CMEs associated with interplanetary radio bursts (Gopalswamy et al. 2001, JGR, 106, 29219). There are many accelerating CMEs in our sample with a speed similar to the ambient solar wind speed. This could be due to selection effect because accelerating CMEs tend to remain visible longer than decelerating ones. We also found that CMEs originating from around the sources of the fast solar wind tend to be faster, indicating that the open magnetic fields above the CME source regions affect the CME propagation.