Turn on the super-elastic collision nature of coronal mass ejections through low approaching speed.

Fang Shen,Xueshang Feng,Yuming Wang,Chenglong Shen

doi:10.1038/srep19576

Abstract

It has been proved from the observations and numerical simulations that the collision between solar coronal mass ejections (CMEs), the largest plasmoids in the heliosphere, could be super-elastic. This finding suggests that the CMEs’ magnetic energy and thermal energy could be converted into kinetic energy through a more efficient way. However CME collisions are not always super-elastic, which means that this distinct property of plasmoids is probably excited conditionally. As the first attempt, we carry out a series of three-dimensional numerical experiments, and establish a diagram showing the dependence of the collision nature on the CME speed and k-number, the ratio of the CME’s kinetic energy to the CME’s total energy. It is found that the super-elastic nature of CMEs appears at the relatively low approaching speed, and most of the previous case studies are in agreement with this diagram. Our study firmly advances the understanding of the super-elastic property of plasmoids, and does give us new clues to deeply understand why and how the magnetic energy and/or thermal energy of the colliding plasmoids can be converted into kinetic energy in such an efficient way.

Highlights

We use the measurements of the interplanetary magnetic field and solar wind plamsa from Wind spacecraft[31,32] to infer the energy density, i.e., the energy per unit volume, of the events of interest at 1 AU
The magnetic energy of a CME decreases by following r−1 when it propagates away from the Sun[34,35], the magnetic energy density follows ωm ∝ r−4 (8)
We may infer the value of the k-number at any given distance as long as its value at 1 AU is known

Summary

Five test cases

We focus on the head-on collision of two identical CMEs, which are modeled as magnetized plasmoids[11,23] (refer to the section of ‘Methods’ for details). It is significantly different from the original critical case of VCME1 = 650 km s−1, and different from the critical case of VCME1 = 400 km s−1 though the values of the k-number of their first CMEs are almost the same. This test suggests that the critical approaching speed, or the boundary between super-elastic and inelastic, is influenced by both CME speed and k-number

Diagram of the collision nature

Comparison with previous observational and simulation cases

Summary and Discussion

Methods

Additional Information