Kinematics of coronal mass ejections between 2 and 30 solar radii

Abstract

Abstract. Kinematics of more than 5000 coronal mass ejections (CMEs) measured in the distance range 2-30 solar radii is investigated. A distinct anticorrelation between the acceleration, a, and the velocity, v, is found. In the linear form, it can be represented as a = −k 1 (v − v 0 ), where v 0 = 400 km s −1 , i.e., most of CMEs faster than 400 km s −1 decelerate, whereas slower ones generally accelerate. After grouping CMEs into the width and mean-distance bins, it was found that the slope k 1 depends on these two parameters: k 1 is smaller for CMEs of larger width and mean-distance. Furthermore, the obtained CME subsets show distinct quadratic-form correlations, of the form a = −k 2 (v − v 0 )|v − v 0 |. The value of k 2 decreases with increasing distance and width, whereas v 0 increases with the distance and is systematically larger than the slow solar wind speed by 100-200 km s −1 . The acceleration-velocity relationship is interpreted as a consequence of the aerodynamic drag. The excess of v 0 over the solar wind speed is explained assuming that in a certain fraction of events the propelling force is still acting in the considered distance range. In most events the inferred propelling force acceleration at 10 solar radii ranges between a L = 0 and 10 m s −2 , being on average smaller at larger distances. However, there are also events that show a L > 50 m s −2 , as well as events indicating a L < 0. Implications for the interplanetary motion of CMEs are discussed, emphasizing the prediction of the 1 a.u. arrival time.

Two types of flare-associated coronal mass ejections

“…Continuous lines represent linear fits to the data point. The AF-CMEs show an anti-correlation of the acceleration and velocity (the slope coefficient of a linear fit = -0.0172), consistent with that obtained by Yashiro et al (2004) and Vršnak et al (2004). The second sample of CMEs (the BFCMEs) does not show a similar trend (the slope coefficient of a linear fit = 0.0012).…”

“…Gosling et al (1976) and MacQueen & Fisher (1983) suggested that different mechanisms could accelerate CMEs associated with prominences and flares. The rapid acceleration of CMEs is strongly correlated with the rising phase of the associated soft X-ray bursts (Zhang et al 2004;Vršnak et al 2004). The flare-associated CMEs are faster and decelerating, while the prominence-associated CMEs are slower and accelerating in the LASCO FOV (St. Cyr et al 1999).…”

The role of aerodynamic drag in propagation of interplanetary coronal mass ejections

“…Taking into account the physical properties of the drag (e.g. Cargill et al 1996;Vršnak 2001a;Cargill 2004;Vršnak et al 2004), it can be presumed that the ICME kinematics depend on speed, mass, and size as well as on the ambient solar-wind density and velocity. Thus the transit time depends intrinsically on a number of parameters, which causes uncertainties in forecasting the ICME arrival.…”

Dynamics of coronal mass ejections in the interplanetary medium

“…The methodology applied in these works consists on the establishment of relationships between the observed data, i.e., the CME initial speed; speeds observed in the interplanetary medium; and the mean acceleration acting on the ICMEs. The studies reported by Vršnak (2001); Vršnak et al (2002Vršnak et al ( , 2004Vršnak et al ( , 2007 may be considered in the same branch, with the difference that in these cases the studies are done, from the point of view of viscous forces acting on the ICMEs. The group of numerical simulation of the transport of ICMEs is more numerous (e.g.…”