Coronal Mass Ejections - Propagation Time and Associated Internal Energy

In this paper, we analyze 91 coronal mass ejection (CME) events studied by Manoharan et al. (2004) and Gopalswamy and Xie (2008). These earth-directed CMEs are large (width $>$160$^\circ$) and cover a wide range of speeds ($\sim$120--2400 {\kmps}) in the LASCO field of view. This set of events also includes interacting CMEs and some of them take longer time to reach 1 AU than the travel time inferred from their speeds at 1 AU. We study the link between the travel time of the CME to 1 AU (combined with its final speed at the Earth) and the effective acceleration in the Sun-Earth distance. Results indicate that (1) for almost all the events (85 out of 91 events), the speed of the CME at 1 AU is always less than or equal to its initial speed measured at the near-Sun region, (2) the distributions of initial speeds, CME-driven shock and CME speeds at 1 AU clearly show the effects of aero-dynamical drag between the CME and the solar wind and in consequence, the speed of the CME tends to equalize to that of the background solar wind, (3) for a large fraction of CMEs (for $\sim$50% of the events), the inferred effective acceleration along the Sun-Earth line dominates the above drag force. The net acceleration suggests an average dissipation of energy $\sim$10$^{31-32}$ ergs, which is likely provided by the Lorentz force associated with the internal magnetic energy carried by the CME.Comment: 18 pages, 6 figure

Propagation characteristics of coronal mass ejections and their effects at the near-Earth environment

276-279This paper deals with the geo-effective analysis of halo and partial halo coronal mass ejections (CMEs) observed during solar cycle 23. The analysis is based on lists of white-light CMEs and associated ICMEs and interplanetary shocks analyzed in recent studies [Manoharan P K, Gopalswamy N, Yashiro S, Lara A, Michalek G & Howard R A, Influence of CME interaction on propagation of interplanetary shocks, J Geophys Res (USA), 109 (2004), 6109, doi:10.1029/2003JA010300; and Manoharan P K, Evolution of Coronal Mass Ejections in the inner heliosphere: A study using white-light and scintillation images 2003, Sol Phys (Netherlands), 235 (2006) pp 345–368, doi: 10.1007/s11207-006-0100-y]. The link between the initial speed of the CME, its speed at 1 AU, speed of the associated IP shock, its strength, magnetic field within the CME and the geomagnetic storm have been studied using the spacecraft data and radio scintillation images from Ooty. The southward component of the CME magnetic field (Bz) and the geo-storm index (Dst) are highly correlated. But a large scatter is evident in this correlation as well as in correlations of speeds of the CME at the near-Sun and at 1 AU with arrival times of IP shock and ICME at the Earth. The preliminary results suggest that each CME has its own unique propagation signature, which is likely determined by the internal energy possessed by the CME and the interaction of the CME with the ambient (i.e., background) solar wind plasma and also with the preceding CME(s) occasionally encountered in the propagation path